path: root/mozglue/baseprofiler/core/platform.cpp

/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* vim: set ts=8 sts=2 et sw=2 tw=80: */
/* This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

// There are three kinds of samples done by the profiler.
//
// - A "periodic" sample is the most complex kind. It is done in response to a
//   timer while the profiler is active. It involves writing a stack trace plus
//   a variety of other values (memory measurements, responsiveness
//   measurements, etc.) into the main ProfileBuffer. The sampling is done from
//   off-thread, and so SuspendAndSampleAndResumeThread() is used to get the
//   register values.
//
// - A "synchronous" sample is a simpler kind. It is done in response to an API
//   call (profiler_get_backtrace()). It involves writing a stack trace and
//   little else into a temporary ProfileBuffer, and wrapping that up in a
//   ProfilerBacktrace that can be subsequently used in a marker. The sampling
//   is done on-thread, and so Registers::SyncPopulate() is used to get the
//   register values.
//
// - A "backtrace" sample is the simplest kind. It is done in response to an
//   API call (profiler_suspend_and_sample_thread()). It involves getting a
//   stack trace via a ProfilerStackCollector; it does not write to a
//   ProfileBuffer. The sampling is done from off-thread, and so uses
//   SuspendAndSampleAndResumeThread() to get the register values.

#include "platform.h"

#include <algorithm>
#include <errno.h>
#include <fstream>
#include <ostream>
#include <set>
#include <sstream>
#include <string_view>

// #include "memory_hooks.h"
#include "mozilla/ArrayUtils.h"
#include "mozilla/AutoProfilerLabel.h"
#include "mozilla/BaseAndGeckoProfilerDetail.h"
#include "mozilla/BaseProfilerDetail.h"
#include "mozilla/DoubleConversion.h"
#include "mozilla/Printf.h"
#include "mozilla/ProfileBufferChunkManagerSingle.h"
#include "mozilla/ProfileBufferChunkManagerWithLocalLimit.h"
#include "mozilla/ProfileChunkedBuffer.h"
#include "mozilla/Services.h"
#include "mozilla/Span.h"
#include "mozilla/StackWalk.h"
#ifdef XP_WIN
#  include "mozilla/StackWalkThread.h"
#endif
#include "mozilla/StaticPtr.h"
#include "mozilla/ThreadLocal.h"
#include "mozilla/TimeStamp.h"
#include "mozilla/Tuple.h"
#include "mozilla/UniquePtr.h"
#include "mozilla/Vector.h"
#include "prdtoa.h"
#include "prtime.h"

#include "BaseProfiler.h"
#include "BaseProfilingCategory.h"
#include "PageInformation.h"
#include "ProfiledThreadData.h"
#include "ProfilerBacktrace.h"
#include "ProfileBuffer.h"
#include "RegisteredThread.h"
#include "BaseProfilerSharedLibraries.h"
#include "ThreadInfo.h"
#include "VTuneProfiler.h"

// Win32 builds always have frame pointers, so FramePointerStackWalk() always
// works.
#if defined(GP_PLAT_x86_windows)
#  define HAVE_NATIVE_UNWIND
#  define USE_FRAME_POINTER_STACK_WALK
#endif

// Win64 builds always omit frame pointers, so we use the slower
// MozStackWalk(), which works in that case.
#if defined(GP_PLAT_amd64_windows)
#  define HAVE_NATIVE_UNWIND
#  define USE_MOZ_STACK_WALK
#endif

// AArch64 Win64 doesn't seem to use frame pointers, so we use the slower
// MozStackWalk().
#if defined(GP_PLAT_arm64_windows)
#  define HAVE_NATIVE_UNWIND
#  define USE_MOZ_STACK_WALK
#endif

// Mac builds use FramePointerStackWalk(). Even if we build without
// frame pointers, we'll still get useful stacks in system libraries
// because those always have frame pointers.
// We don't use MozStackWalk() on Mac.
#if defined(GP_OS_darwin)
#  define HAVE_NATIVE_UNWIND
#  define USE_FRAME_POINTER_STACK_WALK
#endif

// No stack-walking in baseprofiler on linux, android, bsd.
// APIs now make it easier to capture backtraces from the Base Profiler, which
// is currently not supported on these platform, and would lead to a MOZ_CRASH
// in Registers::SyncPopulate(). `#if 0` added in bug 1658232, follow-up bugs
// should be referenced in meta bug 1557568.
#if 0
// Android builds use the ARM Exception Handling ABI to unwind.
#  if defined(GP_PLAT_arm_linux) || defined(GP_PLAT_arm_android)
#    define HAVE_NATIVE_UNWIND
#    define USE_EHABI_STACKWALK
#    include "EHABIStackWalk.h"
#  endif

// Linux/BSD builds use LUL, which uses DWARF info to unwind stacks.
#  if defined(GP_PLAT_amd64_linux) || defined(GP_PLAT_x86_linux) ||       \
      defined(GP_PLAT_amd64_android) || defined(GP_PLAT_x86_android) ||   \
      defined(GP_PLAT_mips64_linux) || defined(GP_PLAT_arm64_linux) ||    \
      defined(GP_PLAT_arm64_android) || defined(GP_PLAT_amd64_freebsd) || \
      defined(GP_PLAT_arm64_freebsd)
#    define HAVE_NATIVE_UNWIND
#    define USE_LUL_STACKWALK
#    include "lul/LulMain.h"
#    include "lul/platform-linux-lul.h"

// On linux we use LUL for periodic samples and synchronous samples, but we use
// FramePointerStackWalk for backtrace samples when MOZ_PROFILING is enabled.
// (See the comment at the top of the file for a definition of
// periodic/synchronous/backtrace.).
//
// FramePointerStackWalk can produce incomplete stacks when the current entry is
// in a shared library without framepointers, however LUL can take a long time
// to initialize, which is undesirable for consumers of
// profiler_suspend_and_sample_thread like the Background Hang Reporter.
#    if defined(MOZ_PROFILING)
#      define USE_FRAME_POINTER_STACK_WALK
#    endif
#  endif
#endif

// We can only stackwalk without expensive initialization on platforms which
// support FramePointerStackWalk or MozStackWalk. LUL Stackwalking requires
// initializing LUL, and EHABIStackWalk requires initializing EHABI, both of
// which can be expensive.
#if defined(USE_FRAME_POINTER_STACK_WALK) || defined(USE_MOZ_STACK_WALK)
#  define HAVE_FASTINIT_NATIVE_UNWIND
#endif

#ifdef MOZ_VALGRIND
#  include <valgrind/memcheck.h>
#else
#  define VALGRIND_MAKE_MEM_DEFINED(_addr, _len) ((void)0)
#endif

#if defined(GP_OS_linux) || defined(GP_OS_android) || defined(GP_OS_freebsd)
#  include <ucontext.h>
#endif

namespace mozilla {
namespace baseprofiler {

using detail::RacyFeatures;

bool LogTest(int aLevelToTest) {
  static const int maxLevel = getenv("MOZ_BASE_PROFILER_VERBOSE_LOGGING") ? 5
                              : getenv("MOZ_BASE_PROFILER_DEBUG_LOGGING") ? 4
                              : getenv("MOZ_BASE_PROFILER_LOGGING")       ? 3
                                                                          : 0;
  return aLevelToTest <= maxLevel;
}

void PrintToConsole(const char* aFmt, ...) {
  va_list args;
  va_start(args, aFmt);
#if defined(ANDROID)
  __android_log_vprint(ANDROID_LOG_INFO, "Gecko", aFmt, args);
#else
  vfprintf(stderr, aFmt, args);
#endif
  va_end(args);
}

ProfileChunkedBuffer& profiler_get_core_buffer() {
  // This needs its own mutex, because it is used concurrently from functions
  // guarded by gPSMutex as well as others without safety (e.g.,
  // profiler_add_marker). It is *not* used inside the critical section of the
  // sampler, because mutexes cannot be used there.
  static ProfileChunkedBuffer sProfileChunkedBuffer{
      ProfileChunkedBuffer::ThreadSafety::WithMutex};
  return sProfileChunkedBuffer;
}

Atomic<int, MemoryOrdering::Relaxed> gSkipSampling;

constexpr static bool ValidateFeatures() {
  int expectedFeatureNumber = 0;

  // Feature numbers should start at 0 and increase by 1 each.
#define CHECK_FEATURE(n_, str_, Name_, desc_) \
  if ((n_) != expectedFeatureNumber) {        \
    return false;                             \
  }                                           \
  ++expectedFeatureNumber;

  BASE_PROFILER_FOR_EACH_FEATURE(CHECK_FEATURE)

#undef CHECK_FEATURE

  return true;
}

static_assert(ValidateFeatures(), "Feature list is invalid");

// Return all features that are available on this platform.
static uint32_t AvailableFeatures() {
  uint32_t features = 0;

#define ADD_FEATURE(n_, str_, Name_, desc_) \
  ProfilerFeature::Set##Name_(features);

  // Add all the possible features.
  BASE_PROFILER_FOR_EACH_FEATURE(ADD_FEATURE)

#undef ADD_FEATURE

  // Now remove features not supported on this platform/configuration.
  ProfilerFeature::ClearJava(features);
  ProfilerFeature::ClearJS(features);
  ProfilerFeature::ClearScreenshots(features);
#if !defined(HAVE_NATIVE_UNWIND)
  ProfilerFeature::ClearStackWalk(features);
#endif
#if !defined(GP_OS_windows)
  ProfilerFeature::ClearNoTimerResolutionChange(features);
#endif

  return features;
}

// Default features common to all contexts (even if not available).
static constexpr uint32_t DefaultFeatures() {
  return ProfilerFeature::Java | ProfilerFeature::JS |
         ProfilerFeature::StackWalk | ProfilerFeature::CPUUtilization |
         ProfilerFeature::ProcessCPU;
}

// Extra default features when MOZ_PROFILER_STARTUP is set (even if not
// available).
static constexpr uint32_t StartupExtraDefaultFeatures() {
  // Enable mainthreadio by default for startup profiles as startup is heavy on
  // I/O operations, and main thread I/O is really important to see there.
  return ProfilerFeature::MainThreadIO | ProfilerFeature::IPCMessages;
}

// The auto-lock/unlock mutex that guards accesses to CorePS and ActivePS.
// Use `PSAutoLock lock;` to take the lock until the end of the enclosing block.
// External profilers may use this same lock for their own data, but as the lock
// is non-recursive, *only* `f(PSLockRef, ...)` functions below should be
// called, to avoid double-locking.
class MOZ_RAII PSAutoLock {
 public:
  PSAutoLock() : mLock(gPSMutex) {}

  PSAutoLock(const PSAutoLock&) = delete;
  void operator=(const PSAutoLock&) = delete;

  [[nodiscard]] static bool IsLockedOnCurrentThread() {
    return gPSMutex.IsLockedOnCurrentThread();
  }

 private:
  static detail::BaseProfilerMutex gPSMutex;
  detail::BaseProfilerAutoLock mLock;
};

detail::BaseProfilerMutex PSAutoLock::gPSMutex{"Base Profiler mutex"};

// Only functions that take a PSLockRef arg can access CorePS's and ActivePS's
// fields.
typedef const PSAutoLock& PSLockRef;

#define PS_GET(type_, name_)      \
  static type_ name_(PSLockRef) { \
    MOZ_ASSERT(sInstance);        \
    return sInstance->m##name_;   \
  }

#define PS_GET_LOCKLESS(type_, name_) \
  static type_ name_() {              \
    MOZ_ASSERT(sInstance);            \
    return sInstance->m##name_;       \
  }

#define PS_GET_AND_SET(type_, name_)                  \
  PS_GET(type_, name_)                                \
  static void Set##name_(PSLockRef, type_ a##name_) { \
    MOZ_ASSERT(sInstance);                            \
    sInstance->m##name_ = a##name_;                   \
  }

// All functions in this file can run on multiple threads unless they have an
// NS_IsMainThread() assertion.

// This class contains the profiler's core global state, i.e. that which is
// valid even when the profiler is not active. Most profile operations can't do
// anything useful when this class is not instantiated, so we release-assert
// its non-nullness in all such operations.
//
// Accesses to CorePS are guarded by gPSMutex. Getters and setters take a
// PSAutoLock reference as an argument as proof that the gPSMutex is currently
// locked. This makes it clear when gPSMutex is locked and helps avoid
// accidental unlocked accesses to global state. There are ways to circumvent
// this mechanism, but please don't do so without *very* good reason and a
// detailed explanation.
//
// The exceptions to this rule:
//
// - mProcessStartTime, because it's immutable;
//
// - each thread's RacyRegisteredThread object is accessible without locking via
//   TLSRegisteredThread::RacyRegisteredThread().
class CorePS {
 private:
  CorePS()
      : mProcessStartTime(TimeStamp::ProcessCreation())
#ifdef USE_LUL_STACKWALK
        ,
        mLul(nullptr)
#endif
  {
  }

  ~CorePS() {}

 public:
  static void Create(PSLockRef aLock) {
    MOZ_ASSERT(!sInstance);
    sInstance = new CorePS();
  }

  static void Destroy(PSLockRef aLock) {
    MOZ_ASSERT(sInstance);
    delete sInstance;
    sInstance = nullptr;
  }

  // Unlike ActivePS::Exists(), CorePS::Exists() can be called without gPSMutex
  // being locked. This is because CorePS is instantiated so early on the main
  // thread that we don't have to worry about it being racy.
  static bool Exists() { return !!sInstance; }

  static void AddSizeOf(PSLockRef, MallocSizeOf aMallocSizeOf,
                        size_t& aProfSize, size_t& aLulSize) {
    MOZ_ASSERT(sInstance);

    aProfSize += aMallocSizeOf(sInstance);

    for (auto& registeredThread : sInstance->mRegisteredThreads) {
      aProfSize += registeredThread->SizeOfIncludingThis(aMallocSizeOf);
    }

    for (auto& registeredPage : sInstance->mRegisteredPages) {
      aProfSize += registeredPage->SizeOfIncludingThis(aMallocSizeOf);
    }

    // Measurement of the following things may be added later if DMD finds it
    // is worthwhile:
    // - CorePS::mRegisteredThreads itself (its elements' children are
    // measured above)
    // - CorePS::mRegisteredPages itself (its elements' children are
    // measured above)
    // - CorePS::mInterposeObserver

#if defined(USE_LUL_STACKWALK)
    if (sInstance->mLul) {
      aLulSize += sInstance->mLul->SizeOfIncludingThis(aMallocSizeOf);
    }
#endif
  }

  // No PSLockRef is needed for this field because it's immutable.
  PS_GET_LOCKLESS(const TimeStamp&, ProcessStartTime)

  PS_GET(const Vector<UniquePtr<RegisteredThread>>&, RegisteredThreads)

  static void AppendRegisteredThread(
      PSLockRef, UniquePtr<RegisteredThread>&& aRegisteredThread) {
    MOZ_ASSERT(sInstance);
    MOZ_RELEASE_ASSERT(
        sInstance->mRegisteredThreads.append(std::move(aRegisteredThread)));
  }

  static void RemoveRegisteredThread(PSLockRef,
                                     RegisteredThread* aRegisteredThread) {
    MOZ_ASSERT(sInstance);
    // Remove aRegisteredThread from mRegisteredThreads.
    for (UniquePtr<RegisteredThread>& rt : sInstance->mRegisteredThreads) {
      if (rt.get() == aRegisteredThread) {
        sInstance->mRegisteredThreads.erase(&rt);
        return;
      }
    }
  }

  PS_GET(Vector<RefPtr<PageInformation>>&, RegisteredPages)

  static void AppendRegisteredPage(PSLockRef,
                                   RefPtr<PageInformation>&& aRegisteredPage) {
    MOZ_ASSERT(sInstance);
    struct RegisteredPageComparator {
      PageInformation* aA;
      bool operator()(PageInformation* aB) const { return aA->Equals(aB); }
    };

    auto foundPageIter = std::find_if(
        sInstance->mRegisteredPages.begin(), sInstance->mRegisteredPages.end(),
        RegisteredPageComparator{aRegisteredPage.get()});

    if (foundPageIter != sInstance->mRegisteredPages.end()) {
      if ((*foundPageIter)->Url() == "about:blank") {
        // When a BrowsingContext is loaded, the first url loaded in it will be
        // about:blank, and if the principal matches, the first document loaded
        // in it will share an inner window. That's why we should delete the
        // intermittent about:blank if they share the inner window.
        sInstance->mRegisteredPages.erase(foundPageIter);
      } else {
        // Do not register the same page again.
        return;
      }
    }
    MOZ_RELEASE_ASSERT(
        sInstance->mRegisteredPages.append(std::move(aRegisteredPage)));
  }

  static void RemoveRegisteredPage(PSLockRef,
                                   uint64_t aRegisteredInnerWindowID) {
    MOZ_ASSERT(sInstance);
    // Remove RegisteredPage from mRegisteredPages by given inner window ID.
    sInstance->mRegisteredPages.eraseIf([&](const RefPtr<PageInformation>& rd) {
      return rd->InnerWindowID() == aRegisteredInnerWindowID;
    });
  }

  static void ClearRegisteredPages(PSLockRef) {
    MOZ_ASSERT(sInstance);
    sInstance->mRegisteredPages.clear();
  }

  PS_GET(const Vector<BaseProfilerCount*>&, Counters)

  static void AppendCounter(PSLockRef, BaseProfilerCount* aCounter) {
    MOZ_ASSERT(sInstance);
    // we don't own the counter; they may be stored in static objects
    MOZ_RELEASE_ASSERT(sInstance->mCounters.append(aCounter));
  }

  static void RemoveCounter(PSLockRef, BaseProfilerCount* aCounter) {
    // we may be called to remove a counter after the profiler is stopped or
    // late in shutdown.
    if (sInstance) {
      auto* counter = std::find(sInstance->mCounters.begin(),
                                sInstance->mCounters.end(), aCounter);
      MOZ_RELEASE_ASSERT(counter != sInstance->mCounters.end());
      sInstance->mCounters.erase(counter);
    }
  }

#ifdef USE_LUL_STACKWALK
  static lul::LUL* Lul(PSLockRef) {
    MOZ_ASSERT(sInstance);
    return sInstance->mLul.get();
  }
  static void SetLul(PSLockRef, UniquePtr<lul::LUL> aLul) {
    MOZ_ASSERT(sInstance);
    sInstance->mLul = std::move(aLul);
  }
#endif

  PS_GET_AND_SET(const std::string&, ProcessName)
  PS_GET_AND_SET(const std::string&, ETLDplus1)

 private:
  // The singleton instance
  static CorePS* sInstance;

  // The time that the process started.
  const TimeStamp mProcessStartTime;

  // Info on all the registered threads.
  // ThreadIds in mRegisteredThreads are unique.
  Vector<UniquePtr<RegisteredThread>> mRegisteredThreads;

  // Info on all the registered pages.
  // InnerWindowIDs in mRegisteredPages are unique.
  Vector<RefPtr<PageInformation>> mRegisteredPages;

  // Non-owning pointers to all active counters
  Vector<BaseProfilerCount*> mCounters;

#ifdef USE_LUL_STACKWALK
  // LUL's state. Null prior to the first activation, non-null thereafter.
  UniquePtr<lul::LUL> mLul;
#endif

  // Process name, provided by child process initialization code.
  std::string mProcessName;
  // Private name, provided by child process initialization code (eTLD+1 in
  // fission)
  std::string mETLDplus1;
};

CorePS* CorePS::sInstance = nullptr;

class SamplerThread;

static SamplerThread* NewSamplerThread(PSLockRef aLock, uint32_t aGeneration,
                                       double aInterval, uint32_t aFeatures);

struct LiveProfiledThreadData {
  RegisteredThread* mRegisteredThread;
  UniquePtr<ProfiledThreadData> mProfiledThreadData;
};

// The buffer size is provided as a number of "entries", this is their size in
// bytes.
constexpr static uint32_t scBytesPerEntry = 8;

// This class contains the profiler's global state that is valid only when the
// profiler is active. When not instantiated, the profiler is inactive.
//
// Accesses to ActivePS are guarded by gPSMutex, in much the same fashion as
// CorePS.
//
class ActivePS {
 private:
  // We need to decide how many chunks of what size we want to fit in the given
  // total maximum capacity for this process, in the (likely) context of
  // multiple processes doing the same choice and having an inter-process
  // mechanism to control the overal memory limit.

  // Minimum chunk size allowed, enough for at least one stack.
  constexpr static uint32_t scMinimumChunkSize =
      2 * ProfileBufferChunkManager::scExpectedMaximumStackSize;

  // Ideally we want at least 2 unreleased chunks to work with (1 current and 1
  // next), and 2 released chunks (so that one can be recycled when old, leaving
  // one with some data).
  constexpr static uint32_t scMinimumNumberOfChunks = 4;

  // And we want to limit chunks to a maximum size, which is a compromise
  // between:
  // - A big size, which helps with reducing the rate of allocations and IPCs.
  // - A small size, which helps with equalizing the duration of recorded data
  //   (as the inter-process controller will discard the oldest chunks in all
  //   Firefox processes).
  constexpr static uint32_t scMaximumChunkSize = 1024 * 1024;

 public:
  // We should be able to store at least the minimum number of the smallest-
  // possible chunks.
  constexpr static uint32_t scMinimumBufferSize =
      scMinimumNumberOfChunks * scMinimumChunkSize;
  constexpr static uint32_t scMinimumBufferEntries =
      scMinimumBufferSize / scBytesPerEntry;

  // Limit to 2GiB.
  constexpr static uint32_t scMaximumBufferSize = 2u * 1024u * 1024u * 1024u;
  constexpr static uint32_t scMaximumBufferEntries =
      scMaximumBufferSize / scBytesPerEntry;

  constexpr static uint32_t ClampToAllowedEntries(uint32_t aEntries) {
    if (aEntries <= scMinimumBufferEntries) {
      return scMinimumBufferEntries;
    }
    if (aEntries >= scMaximumBufferEntries) {
      return scMaximumBufferEntries;
    }
    return aEntries;
  }

 private:
  constexpr static uint32_t ChunkSizeForEntries(uint32_t aEntries) {
    return uint32_t(std::min(size_t(ClampToAllowedEntries(aEntries)) *
                                 scBytesPerEntry / scMinimumNumberOfChunks,
                             size_t(scMaximumChunkSize)));
  }

  static uint32_t AdjustFeatures(uint32_t aFeatures, uint32_t aFilterCount) {
    // Filter out any features unavailable in this platform/configuration.
    aFeatures &= AvailableFeatures();

    // Some features imply others.
    if (aFeatures & ProfilerFeature::FileIOAll) {
      aFeatures |= ProfilerFeature::MainThreadIO | ProfilerFeature::FileIO;
    } else if (aFeatures & ProfilerFeature::FileIO) {
      aFeatures |= ProfilerFeature::MainThreadIO;
    }

    return aFeatures;
  }

  ActivePS(PSLockRef aLock, const TimeStamp& aProfilingStartTime,
           PowerOfTwo32 aCapacity, double aInterval, uint32_t aFeatures,
           const char** aFilters, uint32_t aFilterCount,
           const Maybe<double>& aDuration)
      : mProfilingStartTime(aProfilingStartTime),
        mGeneration(sNextGeneration++),
        mCapacity(aCapacity),
        mDuration(aDuration),
        mInterval(aInterval),
        mFeatures(AdjustFeatures(aFeatures, aFilterCount)),
        mProfileBufferChunkManager(
            MakeUnique<ProfileBufferChunkManagerWithLocalLimit>(
                size_t(ClampToAllowedEntries(aCapacity.Value())) *
                    scBytesPerEntry,
                ChunkSizeForEntries(aCapacity.Value()))),
        mProfileBuffer([this]() -> ProfileChunkedBuffer& {
          ProfileChunkedBuffer& buffer = profiler_get_core_buffer();
          buffer.SetChunkManager(*mProfileBufferChunkManager);
          return buffer;
        }()),
        // The new sampler thread doesn't start sampling immediately because the
        // main loop within Run() is blocked until this function's caller
        // unlocks gPSMutex.
        mSamplerThread(
            NewSamplerThread(aLock, mGeneration, aInterval, aFeatures)),
        mIsPaused(false),
        mIsSamplingPaused(false) {
    // Deep copy and lower-case aFilters.
    MOZ_ALWAYS_TRUE(mFilters.resize(aFilterCount));
    MOZ_ALWAYS_TRUE(mFiltersLowered.resize(aFilterCount));
    for (uint32_t i = 0; i < aFilterCount; ++i) {
      mFilters[i] = aFilters[i];
      mFiltersLowered[i].reserve(mFilters[i].size());
      std::transform(mFilters[i].cbegin(), mFilters[i].cend(),
                     std::back_inserter(mFiltersLowered[i]), ::tolower);
    }
  }

  ~ActivePS() {
    if (mProfileBufferChunkManager) {
      // We still control the chunk manager, remove it from the core buffer.
      profiler_get_core_buffer().ResetChunkManager();
    }
  }

  bool ThreadSelected(const char* aThreadName) {
    if (mFiltersLowered.empty()) {
      return true;
    }

    std::string name = aThreadName;
    std::transform(name.begin(), name.end(), name.begin(), ::tolower);

    for (const auto& filter : mFiltersLowered) {
      if (filter == "*") {
        return true;
      }

      // Crude, non UTF-8 compatible, case insensitive substring search
      if (name.find(filter) != std::string::npos) {
        return true;
      }

      // If the filter is "pid:<my pid>", profile all threads.
      if (mozilla::profiler::detail::FilterHasPid(filter.c_str())) {
        return true;
      }
    }

    return false;
  }

 public:
  static void Create(PSLockRef aLock, const TimeStamp& aProfilingStartTime,
                     PowerOfTwo32 aCapacity, double aInterval,
                     uint32_t aFeatures, const char** aFilters,
                     uint32_t aFilterCount, const Maybe<double>& aDuration) {
    MOZ_ASSERT(!sInstance);
    sInstance = new ActivePS(aLock, aProfilingStartTime, aCapacity, aInterval,
                             aFeatures, aFilters, aFilterCount, aDuration);
  }

  [[nodiscard]] static SamplerThread* Destroy(PSLockRef aLock) {
    MOZ_ASSERT(sInstance);
    auto samplerThread = sInstance->mSamplerThread;
    delete sInstance;
    sInstance = nullptr;

    return samplerThread;
  }

  static bool Exists(PSLockRef) { return !!sInstance; }

  static bool Equals(PSLockRef, PowerOfTwo32 aCapacity,
                     const Maybe<double>& aDuration, double aInterval,
                     uint32_t aFeatures, const char** aFilters,
                     uint32_t aFilterCount) {
    MOZ_ASSERT(sInstance);
    if (sInstance->mCapacity != aCapacity ||
        sInstance->mDuration != aDuration ||
        sInstance->mInterval != aInterval ||
        sInstance->mFeatures != aFeatures ||
        sInstance->mFilters.length() != aFilterCount) {
      return false;
    }

    for (uint32_t i = 0; i < sInstance->mFilters.length(); ++i) {
      if (strcmp(sInstance->mFilters[i].c_str(), aFilters[i]) != 0) {
        return false;
      }
    }
    return true;
  }

  static size_t SizeOf(PSLockRef, MallocSizeOf aMallocSizeOf) {
    MOZ_ASSERT(sInstance);

    size_t n = aMallocSizeOf(sInstance);

    n += sInstance->mProfileBuffer.SizeOfExcludingThis(aMallocSizeOf);

    // Measurement of the following members may be added later if DMD finds it
    // is worthwhile:
    // - mLiveProfiledThreads (both the array itself, and the contents)
    // - mDeadProfiledThreads (both the array itself, and the contents)
    //

    return n;
  }

  static UniquePtr<ProfileBufferChunkManagerWithLocalLimit>
  ExtractBaseProfilerChunkManager(PSLockRef) {
    MOZ_ASSERT(sInstance);
    return std::move(sInstance->mProfileBufferChunkManager);
  }

  static bool ShouldProfileThread(PSLockRef aLock, ThreadInfo* aInfo) {
    MOZ_ASSERT(sInstance);
    return sInstance->ThreadSelected(aInfo->Name());
  }

  PS_GET_LOCKLESS(TimeStamp, ProfilingStartTime)

  PS_GET(uint32_t, Generation)

  PS_GET(PowerOfTwo32, Capacity)

  PS_GET(Maybe<double>, Duration)

  PS_GET(double, Interval)

  PS_GET(uint32_t, Features)

#define PS_GET_FEATURE(n_, str_, Name_, desc_)                \
  static bool Feature##Name_(PSLockRef) {                     \
    MOZ_ASSERT(sInstance);                                    \
    return ProfilerFeature::Has##Name_(sInstance->mFeatures); \
  }

  BASE_PROFILER_FOR_EACH_FEATURE(PS_GET_FEATURE)

#undef PS_GET_FEATURE

  PS_GET(const Vector<std::string>&, Filters)
  PS_GET(const Vector<std::string>&, FiltersLowered)

  static void FulfillChunkRequests(PSLockRef) {
    MOZ_ASSERT(sInstance);
    if (sInstance->mProfileBufferChunkManager) {
      sInstance->mProfileBufferChunkManager->FulfillChunkRequests();
    }
  }

  static ProfileBuffer& Buffer(PSLockRef) {
    MOZ_ASSERT(sInstance);
    return sInstance->mProfileBuffer;
  }

  static const Vector<LiveProfiledThreadData>& LiveProfiledThreads(PSLockRef) {
    MOZ_ASSERT(sInstance);
    return sInstance->mLiveProfiledThreads;
  }

  // Returns an array containing (RegisteredThread*, ProfiledThreadData*) pairs
  // for all threads that should be included in a profile, both for threads
  // that are still registered, and for threads that have been unregistered but
  // still have data in the buffer.
  // For threads that have already been unregistered, the RegisteredThread
  // pointer will be null.
  // The returned array is sorted by thread register time.
  // Do not hold on to the return value across thread registration or profiler
  // restarts.
  static Vector<std::pair<RegisteredThread*, ProfiledThreadData*>>
  ProfiledThreads(PSLockRef) {
    MOZ_ASSERT(sInstance);
    Vector<std::pair<RegisteredThread*, ProfiledThreadData*>> array;
    MOZ_RELEASE_ASSERT(
        array.initCapacity(sInstance->mLiveProfiledThreads.length() +
                           sInstance->mDeadProfiledThreads.length()));
    for (auto& t : sInstance->mLiveProfiledThreads) {
      MOZ_RELEASE_ASSERT(array.append(
          std::make_pair(t.mRegisteredThread, t.mProfiledThreadData.get())));
    }
    for (auto& t : sInstance->mDeadProfiledThreads) {
      MOZ_RELEASE_ASSERT(
          array.append(std::make_pair((RegisteredThread*)nullptr, t.get())));
    }

    std::sort(array.begin(), array.end(),
              [](const std::pair<RegisteredThread*, ProfiledThreadData*>& a,
                 const std::pair<RegisteredThread*, ProfiledThreadData*>& b) {
                return a.second->Info()->RegisterTime() <
                       b.second->Info()->RegisterTime();
              });
    return array;
  }

  static Vector<RefPtr<PageInformation>> ProfiledPages(PSLockRef aLock) {
    MOZ_ASSERT(sInstance);
    Vector<RefPtr<PageInformation>> array;
    for (auto& d : CorePS::RegisteredPages(aLock)) {
      MOZ_RELEASE_ASSERT(array.append(d));
    }
    for (auto& d : sInstance->mDeadProfiledPages) {
      MOZ_RELEASE_ASSERT(array.append(d));
    }
    // We don't need to sort the pages like threads since we won't show them
    // as a list.
    return array;
  }

  // Do a linear search through mLiveProfiledThreads to find the
  // ProfiledThreadData object for a RegisteredThread.
  static ProfiledThreadData* GetProfiledThreadData(
      PSLockRef, RegisteredThread* aRegisteredThread) {
    MOZ_ASSERT(sInstance);
    for (const LiveProfiledThreadData& thread :
         sInstance->mLiveProfiledThreads) {
      if (thread.mRegisteredThread == aRegisteredThread) {
        return thread.mProfiledThreadData.get();
      }
    }
    return nullptr;
  }

  static ProfiledThreadData* AddLiveProfiledThread(
      PSLockRef, RegisteredThread* aRegisteredThread,
      UniquePtr<ProfiledThreadData>&& aProfiledThreadData) {
    MOZ_ASSERT(sInstance);
    MOZ_RELEASE_ASSERT(
        sInstance->mLiveProfiledThreads.append(LiveProfiledThreadData{
            aRegisteredThread, std::move(aProfiledThreadData)}));

    // Return a weak pointer to the ProfiledThreadData object.
    return sInstance->mLiveProfiledThreads.back().mProfiledThreadData.get();
  }

  static void UnregisterThread(PSLockRef aLockRef,
                               RegisteredThread* aRegisteredThread) {
    MOZ_ASSERT(sInstance);

    DiscardExpiredDeadProfiledThreads(aLockRef);

    // Find the right entry in the mLiveProfiledThreads array and remove the
    // element, moving the ProfiledThreadData object for the thread into the
    // mDeadProfiledThreads array.
    // The thread's RegisteredThread object gets destroyed here.
    for (size_t i = 0; i < sInstance->mLiveProfiledThreads.length(); i++) {
      LiveProfiledThreadData& thread = sInstance->mLiveProfiledThreads[i];
      if (thread.mRegisteredThread == aRegisteredThread) {
        thread.mProfiledThreadData->NotifyUnregistered(
            sInstance->mProfileBuffer.BufferRangeEnd());
        MOZ_RELEASE_ASSERT(sInstance->mDeadProfiledThreads.append(
            std::move(thread.mProfiledThreadData)));
        sInstance->mLiveProfiledThreads.erase(
            &sInstance->mLiveProfiledThreads[i]);
        return;
      }
    }
  }

  PS_GET_AND_SET(bool, IsPaused)

  // True if sampling is paused (though generic `SetIsPaused()` or specific
  // `SetIsSamplingPaused()`).
  static bool IsSamplingPaused(PSLockRef lock) {
    MOZ_ASSERT(sInstance);
    return IsPaused(lock) || sInstance->mIsSamplingPaused;
  }

  static void SetIsSamplingPaused(PSLockRef, bool aIsSamplingPaused) {
    MOZ_ASSERT(sInstance);
    sInstance->mIsSamplingPaused = aIsSamplingPaused;
  }

  static void DiscardExpiredDeadProfiledThreads(PSLockRef) {
    MOZ_ASSERT(sInstance);
    uint64_t bufferRangeStart = sInstance->mProfileBuffer.BufferRangeStart();
    // Discard any dead threads that were unregistered before bufferRangeStart.
    sInstance->mDeadProfiledThreads.eraseIf(
        [bufferRangeStart](
            const UniquePtr<ProfiledThreadData>& aProfiledThreadData) {
          Maybe<uint64_t> bufferPosition =
              aProfiledThreadData->BufferPositionWhenUnregistered();
          MOZ_RELEASE_ASSERT(bufferPosition,
                             "should have unregistered this thread");
          return *bufferPosition < bufferRangeStart;
        });
  }

  static void UnregisterPage(PSLockRef aLock,
                             uint64_t aRegisteredInnerWindowID) {
    MOZ_ASSERT(sInstance);
    auto& registeredPages = CorePS::RegisteredPages(aLock);
    for (size_t i = 0; i < registeredPages.length(); i++) {
      RefPtr<PageInformation>& page = registeredPages[i];
      if (page->InnerWindowID() == aRegisteredInnerWindowID) {
        page->NotifyUnregistered(sInstance->mProfileBuffer.BufferRangeEnd());
        MOZ_RELEASE_ASSERT(
            sInstance->mDeadProfiledPages.append(std::move(page)));
        registeredPages.erase(&registeredPages[i--]);
      }
    }
  }

  static void DiscardExpiredPages(PSLockRef) {
    MOZ_ASSERT(sInstance);
    uint64_t bufferRangeStart = sInstance->mProfileBuffer.BufferRangeStart();
    // Discard any dead pages that were unregistered before
    // bufferRangeStart.
    sInstance->mDeadProfiledPages.eraseIf(
        [bufferRangeStart](const RefPtr<PageInformation>& aProfiledPage) {
          Maybe<uint64_t> bufferPosition =
              aProfiledPage->BufferPositionWhenUnregistered();
          MOZ_RELEASE_ASSERT(bufferPosition,
                             "should have unregistered this page");
          return *bufferPosition < bufferRangeStart;
        });
  }

  static void ClearUnregisteredPages(PSLockRef) {
    MOZ_ASSERT(sInstance);
    sInstance->mDeadProfiledPages.clear();
  }

  static void ClearExpiredExitProfiles(PSLockRef) {
    MOZ_ASSERT(sInstance);
    uint64_t bufferRangeStart = sInstance->mProfileBuffer.BufferRangeStart();
    // Discard exit profiles that were gathered before our buffer RangeStart.
    sInstance->mExitProfiles.eraseIf(
        [bufferRangeStart](const ExitProfile& aExitProfile) {
          return aExitProfile.mBufferPositionAtGatherTime < bufferRangeStart;
        });
  }

  static void AddExitProfile(PSLockRef aLock, const std::string& aExitProfile) {
    MOZ_ASSERT(sInstance);

    ClearExpiredExitProfiles(aLock);

    MOZ_RELEASE_ASSERT(sInstance->mExitProfiles.append(
        ExitProfile{aExitProfile, sInstance->mProfileBuffer.BufferRangeEnd()}));
  }

  static Vector<std::string> MoveExitProfiles(PSLockRef aLock) {
    MOZ_ASSERT(sInstance);

    ClearExpiredExitProfiles(aLock);

    Vector<std::string> profiles;
    MOZ_RELEASE_ASSERT(
        profiles.initCapacity(sInstance->mExitProfiles.length()));
    for (auto& profile : sInstance->mExitProfiles) {
      MOZ_RELEASE_ASSERT(profiles.append(std::move(profile.mJSON)));
    }
    sInstance->mExitProfiles.clear();
    return profiles;
  }

 private:
  // The singleton instance.
  static ActivePS* sInstance;

  const TimeStamp mProfilingStartTime;

  // We need to track activity generations. If we didn't we could have the
  // following scenario.
  //
  // - profiler_stop() locks gPSMutex, de-instantiates ActivePS, unlocks
  //   gPSMutex, deletes the SamplerThread (which does a join).
  //
  // - profiler_start() runs on a different thread, locks gPSMutex,
  //   re-instantiates ActivePS, unlocks gPSMutex -- all before the join
  //   completes.
  //
  // - SamplerThread::Run() locks gPSMutex, sees that ActivePS is instantiated,
  //   and continues as if the start/stop pair didn't occur. Also
  //   profiler_stop() is stuck, unable to finish.
  //
  // By checking ActivePS *and* the generation, we can avoid this scenario.
  // sNextGeneration is used to track the next generation number; it is static
  // because it must persist across different ActivePS instantiations.
  const uint32_t mGeneration;
  static uint32_t sNextGeneration;

  // The maximum number of 8-byte entries in mProfileBuffer.
  const PowerOfTwo32 mCapacity;

  // The maximum duration of entries in mProfileBuffer, in seconds.
  const Maybe<double> mDuration;

  // The interval between samples, measured in milliseconds.
  const double mInterval;

  // The profile features that are enabled.
  const uint32_t mFeatures;

  // Substrings of names of threads we want to profile.
  Vector<std::string> mFilters;
  Vector<std::string> mFiltersLowered;

  // The chunk manager used by `mProfileBuffer` below.
  // May become null if it gets transferred to the Gecko Profiler.
  UniquePtr<ProfileBufferChunkManagerWithLocalLimit> mProfileBufferChunkManager;

  // The buffer into which all samples are recorded.
  ProfileBuffer mProfileBuffer;

  // ProfiledThreadData objects for any threads that were profiled at any point
  // during this run of the profiler:
  //  - mLiveProfiledThreads contains all threads that are still registered, and
  //  - mDeadProfiledThreads contains all threads that have already been
  //    unregistered but for which there is still data in the profile buffer.
  Vector<LiveProfiledThreadData> mLiveProfiledThreads;
  Vector<UniquePtr<ProfiledThreadData>> mDeadProfiledThreads;

  // Info on all the dead pages.
  // Registered pages are being moved to this array after unregistration.
  // We are keeping them in case we need them in the profile data.
  // We are removing them when we ensure that we won't need them anymore.
  Vector<RefPtr<PageInformation>> mDeadProfiledPages;

  // The current sampler thread. This class is not responsible for destroying
  // the SamplerThread object; the Destroy() method returns it so the caller
  // can destroy it.
  SamplerThread* const mSamplerThread;

  // Is the profiler fully paused?
  bool mIsPaused;

  // Is the profiler periodic sampling paused?
  bool mIsSamplingPaused;

  struct ExitProfile {
    std::string mJSON;
    uint64_t mBufferPositionAtGatherTime;
  };
  Vector<ExitProfile> mExitProfiles;
};

ActivePS* ActivePS::sInstance = nullptr;
uint32_t ActivePS::sNextGeneration = 0;

#undef PS_GET
#undef PS_GET_LOCKLESS
#undef PS_GET_AND_SET

namespace detail {

TimeStamp GetProfilingStartTime() {
  if (!CorePS::Exists()) {
    return {};
  }
  PSAutoLock lock;
  if (!ActivePS::Exists(lock)) {
    return {};
  }
  return ActivePS::ProfilingStartTime();
}

[[nodiscard]] MFBT_API UniquePtr<ProfileBufferChunkManagerWithLocalLimit>
ExtractBaseProfilerChunkManager() {
  PSAutoLock lock;
  if (MOZ_UNLIKELY(!ActivePS::Exists(lock))) {
    return nullptr;
  }
  return ActivePS::ExtractBaseProfilerChunkManager(lock);
}

}  // namespace detail

Atomic<uint32_t, MemoryOrdering::Relaxed> RacyFeatures::sActiveAndFeatures(0);

/* static */
void RacyFeatures::SetActive(uint32_t aFeatures) {
  sActiveAndFeatures = Active | aFeatures;
}

/* static */
void RacyFeatures::SetInactive() { sActiveAndFeatures = 0; }

/* static */
bool RacyFeatures::IsActive() { return uint32_t(sActiveAndFeatures) & Active; }

/* static */
void RacyFeatures::SetPaused() { sActiveAndFeatures |= Paused; }

/* static */
void RacyFeatures::SetUnpaused() { sActiveAndFeatures &= ~Paused; }

/* static */
void RacyFeatures::SetSamplingPaused() { sActiveAndFeatures |= SamplingPaused; }

/* static */
void RacyFeatures::SetSamplingUnpaused() {
  sActiveAndFeatures &= ~SamplingPaused;
}

/* static */
bool RacyFeatures::IsActiveWithFeature(uint32_t aFeature) {
  uint32_t af = sActiveAndFeatures;  // copy it first
  return (af & Active) && (af & aFeature);
}

/* static */
bool RacyFeatures::IsActiveAndUnpaused() {
  uint32_t af = sActiveAndFeatures;  // copy it first
  return (af & Active) && !(af & Paused);
}

/* static */
bool RacyFeatures::IsActiveAndSamplingUnpaused() {
  uint32_t af = sActiveAndFeatures;  // copy it first
  return (af & Active) && !(af & (Paused | SamplingPaused));
}

// Each live thread has a RegisteredThread, and we store a reference to it in
// TLS. This class encapsulates that TLS.
class TLSRegisteredThread {
 public:
  static bool Init(PSLockRef) {
    bool ok1 = sRegisteredThread.init();
    bool ok2 = AutoProfilerLabel::sProfilingStack.init();
    return ok1 && ok2;
  }

  // Get the entire RegisteredThread. Accesses are guarded by gPSMutex.
  static class RegisteredThread* RegisteredThread(PSLockRef) {
    return sRegisteredThread.get();
  }

  // Get only the RacyRegisteredThread. Accesses are not guarded by gPSMutex.
  static class RacyRegisteredThread* RacyRegisteredThread() {
    class RegisteredThread* registeredThread = sRegisteredThread.get();
    return registeredThread ? &registeredThread->RacyRegisteredThread()
                            : nullptr;
  }

  // Get only the ProfilingStack. Accesses are not guarded by gPSMutex.
  // RacyRegisteredThread() can also be used to get the ProfilingStack, but that
  // is marginally slower because it requires an extra pointer indirection.
  static ProfilingStack* Stack() {
    return AutoProfilerLabel::sProfilingStack.get();
  }

  static void SetRegisteredThread(PSLockRef,
                                  class RegisteredThread* aRegisteredThread) {
    sRegisteredThread.set(aRegisteredThread);
    AutoProfilerLabel::sProfilingStack.set(
        aRegisteredThread
            ? &aRegisteredThread->RacyRegisteredThread().ProfilingStack()
            : nullptr);
  }

 private:
  // This is a non-owning reference to the RegisteredThread;
  // CorePS::mRegisteredThreads is the owning reference. On thread
  // deregistration, this reference is cleared and the RegisteredThread is
  // destroyed.
  static MOZ_THREAD_LOCAL(class RegisteredThread*) sRegisteredThread;
};

MOZ_THREAD_LOCAL(RegisteredThread*) TLSRegisteredThread::sRegisteredThread;

/* static */
ProfilingStack* AutoProfilerLabel::GetProfilingStack() {
  return sProfilingStack.get();
}

// Although you can access a thread's ProfilingStack via
// TLSRegisteredThread::sRegisteredThread, we also have a second TLS pointer
// directly to the ProfilingStack. Here's why.
//
// - We need to be able to push to and pop from the ProfilingStack in
//   AutoProfilerLabel.
//
// - The class functions are hot and must be defined in BaseProfiler.h so they
//   can be inlined.
//
// - We don't want to expose TLSRegisteredThread (and RegisteredThread) in
//   BaseProfiler.h.
//
// This second pointer isn't ideal, but does provide a way to satisfy those
// constraints. TLSRegisteredThread is responsible for updating it.
MOZ_THREAD_LOCAL(ProfilingStack*) AutoProfilerLabel::sProfilingStack;

namespace detail {

[[nodiscard]] MFBT_API TimeStamp GetThreadRegistrationTime() {
  if (!CorePS::Exists()) {
    return {};
  }

  PSAutoLock lock;

  RegisteredThread* registeredThread =
      TLSRegisteredThread::RegisteredThread(lock);
  if (!registeredThread) {
    return {};
  }

  return registeredThread->Info()->RegisterTime();
}

}  // namespace detail

// The name of the main thread.
static const char* const kMainThreadName = "GeckoMain";

////////////////////////////////////////////////////////////////////////
// BEGIN sampling/unwinding code

// The registers used for stack unwinding and a few other sampling purposes.
// The ctor does nothing; users are responsible for filling in the fields.
class Registers {
 public:
  Registers() : mPC{nullptr}, mSP{nullptr}, mFP{nullptr}, mLR{nullptr} {}

#if defined(HAVE_NATIVE_UNWIND)
  // Fills in mPC, mSP, mFP, mLR, and mContext for a synchronous sample.
  void SyncPopulate();
#endif

  void Clear() { memset(this, 0, sizeof(*this)); }

  // These fields are filled in by
  // Sampler::SuspendAndSampleAndResumeThread() for periodic and backtrace
  // samples, and by SyncPopulate() for synchronous samples.
  Address mPC;  // Instruction pointer.
  Address mSP;  // Stack pointer.
  Address mFP;  // Frame pointer.
  Address mLR;  // ARM link register.
#if defined(GP_OS_linux) || defined(GP_OS_android) || defined(GP_OS_freebsd)
  // This contains all the registers, which means it duplicates the four fields
  // above. This is ok.
  ucontext_t* mContext;  // The context from the signal handler.
#endif
};

// Setting MAX_NATIVE_FRAMES too high risks the unwinder wasting a lot of time
// looping on corrupted stacks.
static const size_t MAX_NATIVE_FRAMES = 1024;

struct NativeStack {
  void* mPCs[MAX_NATIVE_FRAMES];
  void* mSPs[MAX_NATIVE_FRAMES];
  size_t mCount;  // Number of frames filled.

  NativeStack() : mPCs(), mSPs(), mCount(0) {}
};

// Merges the profiling stack and native stack, outputting the details to
// aCollector.
static void MergeStacks(uint32_t aFeatures, bool aIsSynchronous,
                        const RegisteredThread& aRegisteredThread,
                        const Registers& aRegs, const NativeStack& aNativeStack,
                        ProfilerStackCollector& aCollector) {
  // WARNING: this function runs within the profiler's "critical section".
  // WARNING: this function might be called while the profiler is inactive, and
  //          cannot rely on ActivePS.

  const ProfilingStack& profilingStack =
      aRegisteredThread.RacyRegisteredThread().ProfilingStack();
  const ProfilingStackFrame* profilingStackFrames = profilingStack.frames;
  uint32_t profilingStackFrameCount = profilingStack.stackSize();

  Maybe<uint64_t> samplePosInBuffer;
  if (!aIsSynchronous) {
    // aCollector.SamplePositionInBuffer() will return Nothing() when
    // profiler_suspend_and_sample_thread is called from the background hang
    // reporter.
    samplePosInBuffer = aCollector.SamplePositionInBuffer();
  }
  // While the profiling stack array is ordered oldest-to-youngest, the JS and
  // native arrays are ordered youngest-to-oldest. We must add frames to aInfo
  // oldest-to-youngest. Thus, iterate over the profiling stack forwards and JS
  // and native arrays backwards. Note: this means the terminating condition
  // jsIndex and nativeIndex is being < 0.
  uint32_t profilingStackIndex = 0;
  int32_t nativeIndex = aNativeStack.mCount - 1;

  uint8_t* lastLabelFrameStackAddr = nullptr;

  // Iterate as long as there is at least one frame remaining.
  while (profilingStackIndex != profilingStackFrameCount || nativeIndex >= 0) {
    // There are 1 to 3 frames available. Find and add the oldest.
    uint8_t* profilingStackAddr = nullptr;
    uint8_t* nativeStackAddr = nullptr;

    if (profilingStackIndex != profilingStackFrameCount) {
      const ProfilingStackFrame& profilingStackFrame =
          profilingStackFrames[profilingStackIndex];

      if (profilingStackFrame.isLabelFrame() ||
          profilingStackFrame.isSpMarkerFrame()) {
        lastLabelFrameStackAddr = (uint8_t*)profilingStackFrame.stackAddress();
      }

      // Skip any JS_OSR frames. Such frames are used when the JS interpreter
      // enters a jit frame on a loop edge (via on-stack-replacement, or OSR).
      // To avoid both the profiling stack frame and jit frame being recorded
      // (and showing up twice), the interpreter marks the interpreter
      // profiling stack frame as JS_OSR to ensure that it doesn't get counted.
      if (profilingStackFrame.isOSRFrame()) {
        profilingStackIndex++;
        continue;
      }

      MOZ_ASSERT(lastLabelFrameStackAddr);
      profilingStackAddr = lastLabelFrameStackAddr;
    }

    if (nativeIndex >= 0) {
      nativeStackAddr = (uint8_t*)aNativeStack.mSPs[nativeIndex];
    }

    // If there's a native stack frame which has the same SP as a profiling
    // stack frame, pretend we didn't see the native stack frame.  Ditto for a
    // native stack frame which has the same SP as a JS stack frame.  In effect
    // this means profiling stack frames or JS frames trump conflicting native
    // frames.
    if (nativeStackAddr && (profilingStackAddr == nativeStackAddr)) {
      nativeStackAddr = nullptr;
      nativeIndex--;
      MOZ_ASSERT(profilingStackAddr);
    }

    // Sanity checks.
    MOZ_ASSERT_IF(profilingStackAddr, profilingStackAddr != nativeStackAddr);
    MOZ_ASSERT_IF(nativeStackAddr, nativeStackAddr != profilingStackAddr);

    // Check to see if profiling stack frame is top-most.
    if (profilingStackAddr > nativeStackAddr) {
      MOZ_ASSERT(profilingStackIndex < profilingStackFrameCount);
      const ProfilingStackFrame& profilingStackFrame =
          profilingStackFrames[profilingStackIndex];

      // Sp marker frames are just annotations and should not be recorded in
      // the profile.
      if (!profilingStackFrame.isSpMarkerFrame()) {
        if (aIsSynchronous && profilingStackFrame.categoryPair() ==
                                  ProfilingCategoryPair::PROFILER) {
          // For stacks captured synchronously (ie. marker stacks), stop
          // walking the stack as soon as we enter the profiler category,
          // to avoid showing profiler internal code in marker stacks.
          return;
        }
        aCollector.CollectProfilingStackFrame(profilingStackFrame);
      }
      profilingStackIndex++;
      continue;
    }

    // If we reach here, there must be a native stack frame and it must be the
    // greatest frame.
    if (nativeStackAddr) {
      MOZ_ASSERT(nativeIndex >= 0);
      void* addr = (void*)aNativeStack.mPCs[nativeIndex];
      aCollector.CollectNativeLeafAddr(addr);
    }
    if (nativeIndex >= 0) {
      nativeIndex--;
    }
  }
}

#if defined(GP_OS_windows) && defined(USE_MOZ_STACK_WALK)
static HANDLE GetThreadHandle(PlatformData* aData);
#endif

#if defined(USE_FRAME_POINTER_STACK_WALK) || defined(USE_MOZ_STACK_WALK)
static void StackWalkCallback(uint32_t aFrameNumber, void* aPC, void* aSP,
                              void* aClosure) {
  NativeStack* nativeStack = static_cast<NativeStack*>(aClosure);
  MOZ_ASSERT(nativeStack->mCount < MAX_NATIVE_FRAMES);
  nativeStack->mSPs[nativeStack->mCount] = aSP;
  nativeStack->mPCs[nativeStack->mCount] = aPC;
  nativeStack->mCount++;
}
#endif

#if defined(USE_FRAME_POINTER_STACK_WALK)
static void DoFramePointerBacktrace(PSLockRef aLock,
                                    const RegisteredThread& aRegisteredThread,
                                    const Registers& aRegs,
                                    NativeStack& aNativeStack) {
  // WARNING: this function runs within the profiler's "critical section".
  // WARNING: this function might be called while the profiler is inactive, and
  //          cannot rely on ActivePS.

  // Start with the current function. We use 0 as the frame number here because
  // the FramePointerStackWalk() call below will use 1..N. This is a bit weird
  // but it doesn't matter because StackWalkCallback() doesn't use the frame
  // number argument.
  StackWalkCallback(/* frameNum */ 0, aRegs.mPC, aRegs.mSP, &aNativeStack);

  uint32_t maxFrames = uint32_t(MAX_NATIVE_FRAMES - aNativeStack.mCount);

  const void* stackEnd = aRegisteredThread.StackTop();
  if (aRegs.mFP >= aRegs.mSP && aRegs.mFP <= stackEnd) {
    FramePointerStackWalk(StackWalkCallback, maxFrames, &aNativeStack,
                          reinterpret_cast<void**>(aRegs.mFP),
                          const_cast<void*>(stackEnd));
  }
}
#endif

#if defined(USE_MOZ_STACK_WALK)
static void DoMozStackWalkBacktrace(PSLockRef aLock,
                                    const RegisteredThread& aRegisteredThread,
                                    const Registers& aRegs,
                                    NativeStack& aNativeStack) {
  // WARNING: this function runs within the profiler's "critical section".
  // WARNING: this function might be called while the profiler is inactive, and
  //          cannot rely on ActivePS.

  // Start with the current function. We use 0 as the frame number here because
  // the MozStackWalkThread() call below will use 1..N. This is a bit weird but
  // it doesn't matter because StackWalkCallback() doesn't use the frame number
  // argument.
  StackWalkCallback(/* frameNum */ 0, aRegs.mPC, aRegs.mSP, &aNativeStack);

  uint32_t maxFrames = uint32_t(MAX_NATIVE_FRAMES - aNativeStack.mCount);

  HANDLE thread = GetThreadHandle(aRegisteredThread.GetPlatformData());
  MOZ_ASSERT(thread);
  MozStackWalkThread(StackWalkCallback, maxFrames, &aNativeStack, thread,
                     /* context */ nullptr);
}
#endif

#ifdef USE_EHABI_STACKWALK
static void DoEHABIBacktrace(PSLockRef aLock,
                             const RegisteredThread& aRegisteredThread,
                             const Registers& aRegs,
                             NativeStack& aNativeStack) {
  // WARNING: this function runs within the profiler's "critical section".
  // WARNING: this function might be called while the profiler is inactive, and
  //          cannot rely on ActivePS.

  aNativeStack.mCount =
      EHABIStackWalk(aRegs.mContext->uc_mcontext,
                     const_cast<void*>(aRegisteredThread.StackTop()),
                     aNativeStack.mSPs, aNativeStack.mPCs, MAX_NATIVE_FRAMES);
}
#endif

#ifdef USE_LUL_STACKWALK

// See the comment at the callsite for why this function is necessary.
#  if defined(MOZ_HAVE_ASAN_BLACKLIST)
MOZ_ASAN_BLACKLIST static void ASAN_memcpy(void* aDst, const void* aSrc,
                                           size_t aLen) {
  // The obvious thing to do here is call memcpy(). However, although
  // ASAN_memcpy() is not instrumented by ASAN, memcpy() still is, and the
  // false positive still manifests! So we must implement memcpy() ourselves
  // within this function.
  char* dst = static_cast<char*>(aDst);
  const char* src = static_cast<const char*>(aSrc);

  for (size_t i = 0; i < aLen; i++) {
    dst[i] = src[i];
  }
}
#  endif

static void DoLULBacktrace(PSLockRef aLock,
                           const RegisteredThread& aRegisteredThread,
                           const Registers& aRegs, NativeStack& aNativeStack) {
  // WARNING: this function runs within the profiler's "critical section".
  // WARNING: this function might be called while the profiler is inactive, and
  //          cannot rely on ActivePS.

  const mcontext_t* mc = &aRegs.mContext->uc_mcontext;

  lul::UnwindRegs startRegs;
  memset(&startRegs, 0, sizeof(startRegs));

#  if defined(GP_PLAT_amd64_linux) || defined(GP_PLAT_amd64_android)
  startRegs.xip = lul::TaggedUWord(mc->gregs[REG_RIP]);
  startRegs.xsp = lul::TaggedUWord(mc->gregs[REG_RSP]);
  startRegs.xbp = lul::TaggedUWord(mc->gregs[REG_RBP]);
#  elif defined(GP_PLAT_amd64_freebsd)
  startRegs.xip = lul::TaggedUWord(mc->mc_rip);
  startRegs.xsp = lul::TaggedUWord(mc->mc_rsp);
  startRegs.xbp = lul::TaggedUWord(mc->mc_rbp);
#  elif defined(GP_PLAT_arm_linux) || defined(GP_PLAT_arm_android)
  startRegs.r15 = lul::TaggedUWord(mc->arm_pc);
  startRegs.r14 = lul::TaggedUWord(mc->arm_lr);
  startRegs.r13 = lul::TaggedUWord(mc->arm_sp);
  startRegs.r12 = lul::TaggedUWord(mc->arm_ip);
  startRegs.r11 = lul::TaggedUWord(mc->arm_fp);
  startRegs.r7 = lul::TaggedUWord(mc->arm_r7);
#  elif defined(GP_PLAT_arm64_linux) || defined(GP_PLAT_arm64_android)
  startRegs.pc = lul::TaggedUWord(mc->pc);
  startRegs.x29 = lul::TaggedUWord(mc->regs[29]);
  startRegs.x30 = lul::TaggedUWord(mc->regs[30]);
  startRegs.sp = lul::TaggedUWord(mc->sp);
#  elif defined(GP_PLAT_arm64_freebsd)
  startRegs.pc = lul::TaggedUWord(mc->mc_gpregs.gp_elr);
  startRegs.x29 = lul::TaggedUWord(mc->mc_gpregs.gp_x[29]);
  startRegs.x30 = lul::TaggedUWord(mc->mc_gpregs.gp_lr);
  startRegs.sp = lul::TaggedUWord(mc->mc_gpregs.gp_sp);
#  elif defined(GP_PLAT_x86_linux) || defined(GP_PLAT_x86_android)
  startRegs.xip = lul::TaggedUWord(mc->gregs[REG_EIP]);
  startRegs.xsp = lul::TaggedUWord(mc->gregs[REG_ESP]);
  startRegs.xbp = lul::TaggedUWord(mc->gregs[REG_EBP]);
#  elif defined(GP_PLAT_mips64_linux)
  startRegs.pc = lul::TaggedUWord(mc->pc);
  startRegs.sp = lul::TaggedUWord(mc->gregs[29]);
  startRegs.fp = lul::TaggedUWord(mc->gregs[30]);
#  else
#    error "Unknown plat"
#  endif

  // Copy up to N_STACK_BYTES from rsp-REDZONE upwards, but not going past the
  // stack's registered top point.  Do some basic sanity checks too.  This
  // assumes that the TaggedUWord holding the stack pointer value is valid, but
  // it should be, since it was constructed that way in the code just above.

  // We could construct |stackImg| so that LUL reads directly from the stack in
  // question, rather than from a copy of it.  That would reduce overhead and
  // space use a bit.  However, it gives a problem with dynamic analysis tools
  // (ASan, TSan, Valgrind) which is that such tools will report invalid or
  // racing memory accesses, and such accesses will be reported deep inside LUL.
  // By taking a copy here, we can either sanitise the copy (for Valgrind) or
  // copy it using an unchecked memcpy (for ASan, TSan).  That way we don't have
  // to try and suppress errors inside LUL.
  //
  // N_STACK_BYTES is set to 160KB.  This is big enough to hold all stacks
  // observed in some minutes of testing, whilst keeping the size of this
  // function (DoNativeBacktrace)'s frame reasonable.  Most stacks observed in
  // practice are small, 4KB or less, and so the copy costs are insignificant
  // compared to other profiler overhead.
  //
  // |stackImg| is allocated on this (the sampling thread's) stack.  That
  // implies that the frame for this function is at least N_STACK_BYTES large.
  // In general it would be considered unacceptable to have such a large frame
  // on a stack, but it only exists for the unwinder thread, and so is not
  // expected to be a problem.  Allocating it on the heap is troublesome because
  // this function runs whilst the sampled thread is suspended, so any heap
  // allocation risks deadlock.  Allocating it as a global variable is not
  // thread safe, which would be a problem if we ever allow multiple sampler
  // threads.  Hence allocating it on the stack seems to be the least-worst
  // option.

  lul::StackImage stackImg;

  {
#  if defined(GP_PLAT_amd64_linux) || defined(GP_PLAT_amd64_android) || \
      defined(GP_PLAT_amd64_freebsd)
    uintptr_t rEDZONE_SIZE = 128;
    uintptr_t start = startRegs.xsp.Value() - rEDZONE_SIZE;
#  elif defined(GP_PLAT_arm_linux) || defined(GP_PLAT_arm_android)
    uintptr_t rEDZONE_SIZE = 0;
    uintptr_t start = startRegs.r13.Value() - rEDZONE_SIZE;
#  elif defined(GP_PLAT_arm64_linux) || defined(GP_PLAT_arm64_android) || \
      defined(GP_PLAT_arm64_freebsd)
    uintptr_t rEDZONE_SIZE = 0;
    uintptr_t start = startRegs.sp.Value() - rEDZONE_SIZE;
#  elif defined(GP_PLAT_x86_linux) || defined(GP_PLAT_x86_android)
    uintptr_t rEDZONE_SIZE = 0;
    uintptr_t start = startRegs.xsp.Value() - rEDZONE_SIZE;
#  elif defined(GP_PLAT_mips64_linux)
    uintptr_t rEDZONE_SIZE = 0;
    uintptr_t start = startRegs.sp.Value() - rEDZONE_SIZE;
#  else
#    error "Unknown plat"
#  endif
    uintptr_t end = reinterpret_cast<uintptr_t>(aRegisteredThread.StackTop());
    uintptr_t ws = sizeof(void*);
    start &= ~(ws - 1);
    end &= ~(ws - 1);
    uintptr_t nToCopy = 0;
    if (start < end) {
      nToCopy = end - start;
      if (nToCopy > lul::N_STACK_BYTES) nToCopy = lul::N_STACK_BYTES;
    }
    MOZ_ASSERT(nToCopy <= lul::N_STACK_BYTES);
    stackImg.mLen = nToCopy;
    stackImg.mStartAvma = start;
    if (nToCopy > 0) {
      // If this is a vanilla memcpy(), ASAN makes the following complaint:
      //
      //   ERROR: AddressSanitizer: stack-buffer-underflow ...
      //   ...
      //   HINT: this may be a false positive if your program uses some custom
      //   stack unwind mechanism or swapcontext
      //
      // This code is very much a custom stack unwind mechanism! So we use an
      // alternative memcpy() implementation that is ignored by ASAN.
#  if defined(MOZ_HAVE_ASAN_BLACKLIST)
      ASAN_memcpy(&stackImg.mContents[0], (void*)start, nToCopy);
#  else
      memcpy(&stackImg.mContents[0], (void*)start, nToCopy);
#  endif
      (void)VALGRIND_MAKE_MEM_DEFINED(&stackImg.mContents[0], nToCopy);
    }
  }

  size_t framePointerFramesAcquired = 0;
  lul::LUL* lul = CorePS::Lul(aLock);
  lul->Unwind(reinterpret_cast<uintptr_t*>(aNativeStack.mPCs),
              reinterpret_cast<uintptr_t*>(aNativeStack.mSPs),
              &aNativeStack.mCount, &framePointerFramesAcquired,
              MAX_NATIVE_FRAMES, &startRegs, &stackImg);

  // Update stats in the LUL stats object.  Unfortunately this requires
  // three global memory operations.
  lul->mStats.mContext += 1;
  lul->mStats.mCFI += aNativeStack.mCount - 1 - framePointerFramesAcquired;
  lul->mStats.mFP += framePointerFramesAcquired;
}

#endif

#ifdef HAVE_NATIVE_UNWIND
static void DoNativeBacktrace(PSLockRef aLock,
                              const RegisteredThread& aRegisteredThread,
                              const Registers& aRegs,
                              NativeStack& aNativeStack) {
  // This method determines which stackwalker is used for periodic and
  // synchronous samples. (Backtrace samples are treated differently, see
  // profiler_suspend_and_sample_thread() for details). The only part of the
  // ordering that matters is that LUL must precede FRAME_POINTER, because on
  // Linux they can both be present.
#  if defined(USE_LUL_STACKWALK)
  DoLULBacktrace(aLock, aRegisteredThread, aRegs, aNativeStack);
#  elif defined(USE_EHABI_STACKWALK)
  DoEHABIBacktrace(aLock, aRegisteredThread, aRegs, aNativeStack);
#  elif defined(USE_FRAME_POINTER_STACK_WALK)
  DoFramePointerBacktrace(aLock, aRegisteredThread, aRegs, aNativeStack);
#  elif defined(USE_MOZ_STACK_WALK)
  DoMozStackWalkBacktrace(aLock, aRegisteredThread, aRegs, aNativeStack);
#  else
#    error "Invalid configuration"
#  endif
}
#endif

// Writes some components shared by periodic and synchronous profiles to
// ActivePS's ProfileBuffer. (This should only be called from DoSyncSample()
// and DoPeriodicSample().)
//
// The grammar for entry sequences is in a comment above
// ProfileBuffer::StreamSamplesToJSON.
static inline void DoSharedSample(
    PSLockRef aLock, bool aIsSynchronous, RegisteredThread& aRegisteredThread,
    const Registers& aRegs, uint64_t aSamplePos, uint64_t aBufferRangeStart,
    ProfileBuffer& aBuffer,
    StackCaptureOptions aCaptureOptions = StackCaptureOptions::Full) {
  // WARNING: this function runs within the profiler's "critical section".

  MOZ_ASSERT(!aBuffer.IsThreadSafe(),
             "Mutexes cannot be used inside this critical section");

  MOZ_RELEASE_ASSERT(ActivePS::Exists(aLock));

  ProfileBufferCollector collector(aBuffer, aSamplePos, aBufferRangeStart);
  NativeStack nativeStack;
#if defined(HAVE_NATIVE_UNWIND)
  if (ActivePS::FeatureStackWalk(aLock) &&
      aCaptureOptions == StackCaptureOptions::Full) {
    DoNativeBacktrace(aLock, aRegisteredThread, aRegs, nativeStack);

    MergeStacks(ActivePS::Features(aLock), aIsSynchronous, aRegisteredThread,
                aRegs, nativeStack, collector);
  } else
#endif
  {
    MergeStacks(ActivePS::Features(aLock), aIsSynchronous, aRegisteredThread,
                aRegs, nativeStack, collector);

    // We can't walk the whole native stack, but we can record the top frame.
    if (aCaptureOptions == StackCaptureOptions::Full) {
      aBuffer.AddEntry(ProfileBufferEntry::NativeLeafAddr((void*)aRegs.mPC));
    }
  }
}

// Writes the components of a synchronous sample to the given ProfileBuffer.
static void DoSyncSample(PSLockRef aLock, RegisteredThread& aRegisteredThread,
                         const TimeStamp& aNow, const Registers& aRegs,
                         ProfileBuffer& aBuffer,
                         StackCaptureOptions aCaptureOptions) {
  // WARNING: this function runs within the profiler's "critical section".

  MOZ_ASSERT(aCaptureOptions != StackCaptureOptions::NoStack,
             "DoSyncSample should not be called when no capture is needed");

  const uint64_t bufferRangeStart = aBuffer.BufferRangeStart();

  const uint64_t samplePos =
      aBuffer.AddThreadIdEntry(aRegisteredThread.Info()->ThreadId());

  TimeDuration delta = aNow - CorePS::ProcessStartTime();
  aBuffer.AddEntry(ProfileBufferEntry::Time(delta.ToMilliseconds()));

  DoSharedSample(aLock, /* aIsSynchronous = */ true, aRegisteredThread, aRegs,
                 samplePos, bufferRangeStart, aBuffer, aCaptureOptions);
}

// Writes the components of a periodic sample to ActivePS's ProfileBuffer.
// The ThreadId entry is already written in the main ProfileBuffer, its location
// is `aSamplePos`, we can write the rest to `aBuffer` (which may be different).
static void DoPeriodicSample(PSLockRef aLock,
                             RegisteredThread& aRegisteredThread,
                             ProfiledThreadData& aProfiledThreadData,
                             const Registers& aRegs, uint64_t aSamplePos,
                             uint64_t aBufferRangeStart,
                             ProfileBuffer& aBuffer) {
  // WARNING: this function runs within the profiler's "critical section".

  DoSharedSample(aLock, /* aIsSynchronous = */ false, aRegisteredThread, aRegs,
                 aSamplePos, aBufferRangeStart, aBuffer);
}

// END sampling/unwinding code
////////////////////////////////////////////////////////////////////////

////////////////////////////////////////////////////////////////////////
// BEGIN saving/streaming code

const static uint64_t kJS_MAX_SAFE_UINTEGER = +9007199254740991ULL;

static int64_t SafeJSInteger(uint64_t aValue) {
  return aValue <= kJS_MAX_SAFE_UINTEGER ? int64_t(aValue) : -1;
}

static void AddSharedLibraryInfoToStream(JSONWriter& aWriter,
                                         const SharedLibrary& aLib) {
  aWriter.StartObjectElement();
  aWriter.IntProperty("start", SafeJSInteger(aLib.GetStart()));
  aWriter.IntProperty("end", SafeJSInteger(aLib.GetEnd()));
  aWriter.IntProperty("offset", SafeJSInteger(aLib.GetOffset()));
  aWriter.StringProperty("name", aLib.GetModuleName());
  aWriter.StringProperty("path", aLib.GetModulePath());
  aWriter.StringProperty("debugName", aLib.GetDebugName());
  aWriter.StringProperty("debugPath", aLib.GetDebugPath());
  aWriter.StringProperty("breakpadId", aLib.GetBreakpadId());
  aWriter.StringProperty("arch", aLib.GetArch());
  aWriter.EndObject();
}

void AppendSharedLibraries(JSONWriter& aWriter) {
  SharedLibraryInfo info = SharedLibraryInfo::GetInfoForSelf();
  info.SortByAddress();
  for (size_t i = 0; i < info.GetSize(); i++) {
    AddSharedLibraryInfoToStream(aWriter, info.GetEntry(i));
  }
}

static void StreamCategories(SpliceableJSONWriter& aWriter) {
  // Same order as ProfilingCategory. Format:
  // [
  //   {
  //     name: "Idle",
  //     color: "transparent",
  //     subcategories: ["Other"],
  //   },
  //   {
  //     name: "Other",
  //     color: "grey",
  //     subcategories: [
  //       "JSM loading",
  //       "Subprocess launching",
  //       "DLL loading"
  //     ]
  //   },
  //   ...
  // ]

#define CATEGORY_JSON_BEGIN_CATEGORY(name, labelAsString, color) \
  aWriter.Start();                                               \
  aWriter.StringProperty("name", labelAsString);                 \
  aWriter.StringProperty("color", color);                        \
  aWriter.StartArrayProperty("subcategories");
#define CATEGORY_JSON_SUBCATEGORY(supercategory, name, labelAsString) \
  aWriter.StringElement(labelAsString);
#define CATEGORY_JSON_END_CATEGORY \
  aWriter.EndArray();              \
  aWriter.EndObject();

  MOZ_PROFILING_CATEGORY_LIST(CATEGORY_JSON_BEGIN_CATEGORY,
                              CATEGORY_JSON_SUBCATEGORY,
                              CATEGORY_JSON_END_CATEGORY)

#undef CATEGORY_JSON_BEGIN_CATEGORY
#undef CATEGORY_JSON_SUBCATEGORY
#undef CATEGORY_JSON_END_CATEGORY
}

static void StreamMarkerSchema(SpliceableJSONWriter& aWriter) {
  // Get an array view with all registered marker-type-specific functions.
  base_profiler_markers_detail::Streaming::LockedMarkerTypeFunctionsList
      markerTypeFunctionsArray;
  // List of streamed marker names, this is used to spot duplicates.
  std::set<std::string> names;
  // Stream the display schema for each different one. (Duplications may come
  // from the same code potentially living in different libraries.)
  for (const auto& markerTypeFunctions : markerTypeFunctionsArray) {
    auto name = markerTypeFunctions.mMarkerTypeNameFunction();
    // std::set.insert(T&&) returns a pair, its `second` is true if the element
    // was actually inserted (i.e., it was not there yet.)
    const bool didInsert =
        names.insert(std::string(name.data(), name.size())).second;
    if (didInsert) {
      markerTypeFunctions.mMarkerSchemaFunction().Stream(aWriter, name);
    }
  }
}

static int64_t MicrosecondsSince1970();

static void StreamMetaJSCustomObject(PSLockRef aLock,
                                     SpliceableJSONWriter& aWriter,
                                     bool aIsShuttingDown) {
  MOZ_RELEASE_ASSERT(CorePS::Exists() && ActivePS::Exists(aLock));

  aWriter.IntProperty("version", 26);

  // The "startTime" field holds the number of milliseconds since midnight
  // January 1, 1970 GMT. This grotty code computes (Now - (Now -
  // ProcessStartTime)) to convert CorePS::ProcessStartTime() into that form.
  // Note: This is the only absolute time in the profile! All other timestamps
  // are relative to this startTime.
  TimeDuration delta = TimeStamp::Now() - CorePS::ProcessStartTime();
  aWriter.DoubleProperty(
      "startTime", MicrosecondsSince1970() / 1000.0 - delta.ToMilliseconds());

  aWriter.DoubleProperty("profilingStartTime", (ActivePS::ProfilingStartTime() -
                                                CorePS::ProcessStartTime())
                                                   .ToMilliseconds());

  if (const TimeStamp contentEarliestTime =
          ActivePS::Buffer(aLock)
              .UnderlyingChunkedBuffer()
              .GetEarliestChunkStartTimeStamp();
      !contentEarliestTime.IsNull()) {
    aWriter.DoubleProperty(
        "contentEarliestTime",
        (contentEarliestTime - CorePS::ProcessStartTime()).ToMilliseconds());
  } else {
    aWriter.NullProperty("contentEarliestTime");
  }

  const double profilingEndTime = profiler_time();
  aWriter.DoubleProperty("profilingEndTime", profilingEndTime);

  if (aIsShuttingDown) {
    aWriter.DoubleProperty("shutdownTime", profilingEndTime);
  } else {
    aWriter.NullProperty("shutdownTime");
  }

  aWriter.StartArrayProperty("categories");
  StreamCategories(aWriter);
  aWriter.EndArray();

  aWriter.StartArrayProperty("markerSchema");
  StreamMarkerSchema(aWriter);
  aWriter.EndArray();

  if (!profiler_is_main_thread()) {
    // Leave the rest of the properties out if we're not on the main thread.
    // At the moment, the only case in which this function is called on a
    // background thread is if we're in a content process and are going to
    // send this profile to the parent process. In that case, the parent
    // process profile's "meta" object already has the rest of the properties,
    // and the parent process profile is dumped on that process's main thread.
    return;
  }

  aWriter.DoubleProperty("interval", ActivePS::Interval(aLock));
  aWriter.IntProperty("stackwalk", ActivePS::FeatureStackWalk(aLock));

#ifdef DEBUG
  aWriter.IntProperty("debug", 1);
#else
  aWriter.IntProperty("debug", 0);
#endif

  aWriter.IntProperty("gcpoison", 0);

  aWriter.IntProperty("asyncstack", 0);

  aWriter.IntProperty("processType", 0);
}

static void StreamPages(PSLockRef aLock, SpliceableJSONWriter& aWriter) {
  MOZ_RELEASE_ASSERT(CorePS::Exists());
  ActivePS::DiscardExpiredPages(aLock);
  for (const auto& page : ActivePS::ProfiledPages(aLock)) {
    page->StreamJSON(aWriter);
  }
}

static void locked_profiler_stream_json_for_this_process(
    PSLockRef aLock, SpliceableJSONWriter& aWriter, double aSinceTime,
    bool aIsShuttingDown, bool aOnlyThreads = false) {
  LOG("locked_profiler_stream_json_for_this_process");

  MOZ_RELEASE_ASSERT(CorePS::Exists() && ActivePS::Exists(aLock));

  AUTO_PROFILER_STATS(base_locked_profiler_stream_json_for_this_process);

  const double collectionStartMs = profiler_time();

  ProfileBuffer& buffer = ActivePS::Buffer(aLock);

  // If there is a set "Window length", discard older data.
  Maybe<double> durationS = ActivePS::Duration(aLock);
  if (durationS.isSome()) {
    const double durationStartMs = collectionStartMs - *durationS * 1000;
    buffer.DiscardSamplesBeforeTime(durationStartMs);
  }

  if (!aOnlyThreads) {
    // Put shared library info
    aWriter.StartArrayProperty("libs");
    AppendSharedLibraries(aWriter);
    aWriter.EndArray();

    // Put meta data
    aWriter.StartObjectProperty("meta");
    { StreamMetaJSCustomObject(aLock, aWriter, aIsShuttingDown); }
    aWriter.EndObject();

    // Put page data
    aWriter.StartArrayProperty("pages");
    { StreamPages(aLock, aWriter); }
    aWriter.EndArray();

    buffer.StreamProfilerOverheadToJSON(aWriter, CorePS::ProcessStartTime(),
                                        aSinceTime);
    buffer.StreamCountersToJSON(aWriter, CorePS::ProcessStartTime(),
                                aSinceTime);

    // Lists the samples for each thread profile
    aWriter.StartArrayProperty("threads");
  }

  // if aOnlyThreads is true, the only output will be the threads array items.
  {
    ActivePS::DiscardExpiredDeadProfiledThreads(aLock);
    Vector<std::pair<RegisteredThread*, ProfiledThreadData*>> threads =
        ActivePS::ProfiledThreads(aLock);
    for (auto& thread : threads) {
      ProfiledThreadData* profiledThreadData = thread.second;
      profiledThreadData->StreamJSON(
          buffer, aWriter, CorePS::ProcessName(aLock), CorePS::ETLDplus1(aLock),
          CorePS::ProcessStartTime(), aSinceTime);
    }
  }

  if (!aOnlyThreads) {
    aWriter.EndArray();

    aWriter.StartArrayProperty("pausedRanges");
    { buffer.StreamPausedRangesToJSON(aWriter, aSinceTime); }
    aWriter.EndArray();
  }

  const double collectionEndMs = profiler_time();

  // Record timestamps for the collection into the buffer, so that consumers
  // know why we didn't collect any samples for its duration.
  // We put these entries into the buffer after we've collected the profile,
  // so they'll be visible for the *next* profile collection (if they haven't
  // been overwritten due to buffer wraparound by then).
  buffer.AddEntry(ProfileBufferEntry::CollectionStart(collectionStartMs));
  buffer.AddEntry(ProfileBufferEntry::CollectionEnd(collectionEndMs));
}

bool profiler_stream_json_for_this_process(SpliceableJSONWriter& aWriter,
                                           double aSinceTime,
                                           bool aIsShuttingDown,
                                           bool aOnlyThreads) {
  LOG("profiler_stream_json_for_this_process");

  MOZ_RELEASE_ASSERT(CorePS::Exists());

  PSAutoLock lock;

  if (!ActivePS::Exists(lock)) {
    return false;
  }

  locked_profiler_stream_json_for_this_process(lock, aWriter, aSinceTime,
                                               aIsShuttingDown, aOnlyThreads);
  return true;
}

// END saving/streaming code
////////////////////////////////////////////////////////////////////////

static char FeatureCategory(uint32_t aFeature) {
  if (aFeature & DefaultFeatures()) {
    if (aFeature & AvailableFeatures()) {
      return 'D';
    }
    return 'd';
  }

  if (aFeature & StartupExtraDefaultFeatures()) {
    if (aFeature & AvailableFeatures()) {
      return 'S';
    }
    return 's';
  }

  if (aFeature & AvailableFeatures()) {
    return '-';
  }
  return 'x';
}

static void PrintUsage() {
  PrintToConsole(
      "\n"
      "Profiler environment variable usage:\n"
      "\n"
      "  MOZ_BASE_PROFILER_HELP\n"
      "  If set to any value, prints this message.\n"
      "  (Only BaseProfiler features are known here; Use MOZ_PROFILER_HELP\n"
      "  for Gecko Profiler help, with more features).\n"
      "\n"
      "  MOZ_BASE_PROFILER_{,DEBUG_,VERBOSE}LOGGING\n"
      "  Enables BaseProfiler logging to stdout. The levels of logging\n"
      "  available are MOZ_BASE_PROFILER_LOGGING' (least verbose),\n"
      "  '..._DEBUG_LOGGING', '..._VERBOSE_LOGGING' (most verbose)\n"
      "\n"
      "  MOZ_PROFILER_STARTUP\n"
      "  If set to any value other than '' or '0'/'N'/'n', starts the\n"
      "  profiler immediately on start-up.\n"
      "  Useful if you want profile code that runs very early.\n"
      "\n"
      "  MOZ_PROFILER_STARTUP_ENTRIES=<%u..%u>\n"
      "  If MOZ_PROFILER_STARTUP is set, specifies the number of entries\n"
      "  per process in the profiler's circular buffer when the profiler is\n"
      "  first started.\n"
      "  If unset, the platform default is used:\n"
      "  %u entries per process, or %u when MOZ_PROFILER_STARTUP is set.\n"
      "  (%u bytes per entry -> %u or %u total bytes per process)\n"
      "  Optional units in bytes: KB, KiB, MB, MiB, GB, GiB\n"
      "\n"
      "  MOZ_PROFILER_STARTUP_DURATION=<1..>\n"
      "  If MOZ_PROFILER_STARTUP is set, specifies the maximum life time\n"
      "  of entries in the the profiler's circular buffer when the profiler\n"
      "  is first started, in seconds.\n"
      "  If unset, the life time of the entries will only be restricted by\n"
      "  MOZ_PROFILER_STARTUP_ENTRIES (or its default value), and no\n"
      "  additional time duration restriction will be applied.\n"
      "\n"
      "  MOZ_PROFILER_STARTUP_INTERVAL=<1..1000>\n"
      "  If MOZ_PROFILER_STARTUP is set, specifies the sample interval,\n"
      "  measured in milliseconds, when the profiler is first started.\n"
      "  If unset, the platform default is used.\n"
      "\n"
      "  MOZ_PROFILER_STARTUP_FEATURES_BITFIELD=<Number>\n"
      "  If MOZ_PROFILER_STARTUP is set, specifies the profiling\n"
      "  features, as the integer value of the features bitfield.\n"
      "  If unset, the value from MOZ_PROFILER_STARTUP_FEATURES is used.\n"
      "\n"
      "  MOZ_PROFILER_STARTUP_FEATURES=<Features>\n"
      "  If MOZ_PROFILER_STARTUP is set, specifies the profiling\n"
      "  features, as a comma-separated list of strings.\n"
      "  Ignored if MOZ_PROFILER_STARTUP_FEATURES_BITFIELD is set.\n"
      "  If unset, the platform default is used.\n"
      "\n"
      "    Features: (x=unavailable, D/d=default/unavailable,\n"
      "               S/s=MOZ_PROFILER_STARTUP extra "
      "default/unavailable)\n",
      unsigned(ActivePS::scMinimumBufferEntries),
      unsigned(ActivePS::scMaximumBufferEntries),
      unsigned(BASE_PROFILER_DEFAULT_ENTRIES.Value()),
      unsigned(BASE_PROFILER_DEFAULT_STARTUP_ENTRIES.Value()),
      unsigned(scBytesPerEntry),
      unsigned(BASE_PROFILER_DEFAULT_ENTRIES.Value() * scBytesPerEntry),
      unsigned(BASE_PROFILER_DEFAULT_STARTUP_ENTRIES.Value() *
               scBytesPerEntry));

#define PRINT_FEATURE(n_, str_, Name_, desc_)             \
  PrintToConsole("    %c %7u: \"%s\" (%s)\n",             \
                 FeatureCategory(ProfilerFeature::Name_), \
                 ProfilerFeature::Name_, str_, desc_);

  BASE_PROFILER_FOR_EACH_FEATURE(PRINT_FEATURE)

#undef PRINT_FEATURE

  PrintToConsole(
      "    -          \"default\" (All above D+S defaults)\n"
      "\n"
      "  MOZ_PROFILER_STARTUP_FILTERS=<Filters>\n"
      "  If MOZ_PROFILER_STARTUP is set, specifies the thread filters, as "
      "a\n"
      "  comma-separated list of strings. A given thread will be sampled if\n"
      "  any of the filters is a case-insensitive substring of the thread\n"
      "  name. If unset, a default is used.\n"
      "\n"
      "  MOZ_PROFILER_SHUTDOWN\n"
      "  If set, the profiler saves a profile to the named file on shutdown.\n"
      "\n"
      "  MOZ_PROFILER_SYMBOLICATE\n"
      "  If set, the profiler will pre-symbolicate profiles.\n"
      "  *Note* This will add a significant pause when gathering data, and\n"
      "  is intended mainly for local development.\n"
      "\n"
      "  MOZ_PROFILER_LUL_TEST\n"
      "  If set to any value, runs LUL unit tests at startup.\n"
      "\n"
      "  This platform %s native unwinding.\n"
      "\n",
#if defined(HAVE_NATIVE_UNWIND)
      "supports"
#else
      "does not support"
#endif
  );
}

////////////////////////////////////////////////////////////////////////
// BEGIN Sampler

#if defined(GP_OS_linux) || defined(GP_OS_android)
struct SigHandlerCoordinator;
#endif

// Sampler performs setup and teardown of the state required to sample with the
// profiler. Sampler may exist when ActivePS is not present.
//
// SuspendAndSampleAndResumeThread must only be called from a single thread,
// and must not sample the thread it is being called from. A separate Sampler
// instance must be used for each thread which wants to capture samples.

// WARNING WARNING WARNING WARNING WARNING WARNING WARNING WARNING
//
// With the exception of SamplerThread, all Sampler objects must be Disable-d
// before releasing the lock which was used to create them. This avoids races
// on linux with the SIGPROF signal handler.

class Sampler {
 public:
  // Sets up the profiler such that it can begin sampling.
  explicit Sampler(PSLockRef aLock);

  // Disable the sampler, restoring it to its previous state. This must be
  // called once, and only once, before the Sampler is destroyed.
  void Disable(PSLockRef aLock);

  // This method suspends and resumes the samplee thread. It calls the passed-in
  // function-like object aProcessRegs (passing it a populated |const
  // Registers&| arg) while the samplee thread is suspended.
  //
  // Func must be a function-like object of type `void()`.
  template <typename Func>
  void SuspendAndSampleAndResumeThread(
      PSLockRef aLock, const RegisteredThread& aRegisteredThread,
      const TimeStamp& aNow, const Func& aProcessRegs);

 private:
#if defined(GP_OS_linux) || defined(GP_OS_android) || defined(GP_OS_freebsd)
  // Used to restore the SIGPROF handler when ours is removed.
  struct sigaction mOldSigprofHandler;

  // This process' ID. Needed as an argument for tgkill in
  // SuspendAndSampleAndResumeThread.
  BaseProfilerProcessId mMyPid;

  // The sampler thread's ID.  Used to assert that it is not sampling itself,
  // which would lead to deadlock.
  BaseProfilerThreadId mSamplerTid;

 public:
  // This is the one-and-only variable used to communicate between the sampler
  // thread and the samplee thread's signal handler. It's static because the
  // samplee thread's signal handler is static.
  static struct SigHandlerCoordinator* sSigHandlerCoordinator;
#endif
};

// END Sampler
////////////////////////////////////////////////////////////////////////

////////////////////////////////////////////////////////////////////////
// BEGIN SamplerThread

// The sampler thread controls sampling and runs whenever the profiler is
// active. It periodically runs through all registered threads, finds those
// that should be sampled, then pauses and samples them.

class SamplerThread {
 public:
  // Creates a sampler thread, but doesn't start it.
  SamplerThread(PSLockRef aLock, uint32_t aActivityGeneration,
                double aIntervalMilliseconds, uint32_t aFeatures);
  ~SamplerThread();

  // This runs on (is!) the sampler thread.
  void Run();

  // This runs on the main thread.
  void Stop(PSLockRef aLock);

 private:
  // This suspends the calling thread for the given number of microseconds.
  // Best effort timing.
  void SleepMicro(uint32_t aMicroseconds);

  // The sampler used to suspend and sample threads.
  Sampler mSampler;

  // The activity generation, for detecting when the sampler thread must stop.
  const uint32_t mActivityGeneration;

  // The interval between samples, measured in microseconds.
  const int mIntervalMicroseconds;

  // The OS-specific handle for the sampler thread.
#if defined(GP_OS_windows)
  HANDLE mThread;
#elif defined(GP_OS_darwin) || defined(GP_OS_linux) || \
    defined(GP_OS_android) || defined(GP_OS_freebsd)
  pthread_t mThread;
#endif

#if defined(GP_OS_windows)
  bool mNoTimerResolutionChange = true;
#endif

  SamplerThread(const SamplerThread&) = delete;
  void operator=(const SamplerThread&) = delete;
};

// This function is required because we need to create a SamplerThread within
// ActivePS's constructor, but SamplerThread is defined after ActivePS. It
// could probably be removed by moving some code around.
static SamplerThread* NewSamplerThread(PSLockRef aLock, uint32_t aGeneration,
                                       double aInterval, uint32_t aFeatures) {
  return new SamplerThread(aLock, aGeneration, aInterval, aFeatures);
}

// This function is the sampler thread.  This implementation is used for all
// targets.
void SamplerThread::Run() {
  // TODO: If possible, name this thread later on, after NSPR becomes available.
  // PR_SetCurrentThreadName("SamplerThread");

  // Features won't change during this SamplerThread's lifetime, so we can read
  // them once and store them locally.
  const uint32_t features = []() -> uint32_t {
    PSAutoLock lock;
    if (!ActivePS::Exists(lock)) {
      // If there is no active profiler, it doesn't matter what we return,
      // because this thread will exit before any feature is used.
      return 0;
    }
    return ActivePS::Features(lock);
  }();

  // Not *no*-stack-sampling means we do want stack sampling.
  const bool stackSampling = !ProfilerFeature::HasNoStackSampling(features);

  // Use local BlocksRingBuffer&ProfileBuffer to capture the stack.
  // (This is to avoid touching the CorePS::CoreBuffer lock while
  // a thread is suspended, because that thread could be working with
  // the CorePS::CoreBuffer as well.)
  ProfileBufferChunkManagerSingle localChunkManager(
      ProfileBufferChunkManager::scExpectedMaximumStackSize);
  ProfileChunkedBuffer localBuffer(
      ProfileChunkedBuffer::ThreadSafety::WithoutMutex, localChunkManager);
  ProfileBuffer localProfileBuffer(localBuffer);

  // Will be kept between collections, to know what each collection does.
  auto previousState = localBuffer.GetState();

  // This will be positive if we are running behind schedule (sampling less
  // frequently than desired) and negative if we are ahead of schedule.
  TimeDuration lastSleepOvershoot = 0;
  TimeStamp sampleStart = TimeStamp::Now();

  while (true) {
    // This scope is for |lock|. It ends before we sleep below.
    {
      PSAutoLock lock;
      TimeStamp lockAcquired = TimeStamp::Now();

      if (!ActivePS::Exists(lock)) {
        return;
      }

      // At this point profiler_stop() might have been called, and
      // profiler_start() might have been called on another thread. If this
      // happens the generation won't match.
      if (ActivePS::Generation(lock) != mActivityGeneration) {
        return;
      }

      ActivePS::ClearExpiredExitProfiles(lock);

      TimeStamp expiredMarkersCleaned = TimeStamp::Now();

      if (int(gSkipSampling) <= 0 && !ActivePS::IsSamplingPaused(lock)) {
        TimeDuration delta = sampleStart - CorePS::ProcessStartTime();
        ProfileBuffer& buffer = ActivePS::Buffer(lock);

        // handle per-process generic counters
        const Vector<BaseProfilerCount*>& counters = CorePS::Counters(lock);
        for (auto& counter : counters) {
          // create Buffer entries for each counter
          buffer.AddEntry(ProfileBufferEntry::CounterId(counter));
          buffer.AddEntry(ProfileBufferEntry::Time(delta.ToMilliseconds()));
          // XXX support keyed maps of counts
          // In the future, we'll support keyed counters - for example, counters
          // with a key which is a thread ID. For "simple" counters we'll just
          // use a key of 0.
          int64_t count;
          uint64_t number;
          counter->Sample(count, number);
          buffer.AddEntry(ProfileBufferEntry::CounterKey(0));
          buffer.AddEntry(ProfileBufferEntry::Count(count));
          if (number) {
            buffer.AddEntry(ProfileBufferEntry::Number(number));
          }
        }
        TimeStamp countersSampled = TimeStamp::Now();

        if (stackSampling) {
          const Vector<LiveProfiledThreadData>& liveThreads =
              ActivePS::LiveProfiledThreads(lock);

          for (auto& thread : liveThreads) {
            RegisteredThread* registeredThread = thread.mRegisteredThread;
            ProfiledThreadData* profiledThreadData =
                thread.mProfiledThreadData.get();
            RefPtr<ThreadInfo> info = registeredThread->Info();

            // If the thread is asleep and has been sampled before in the same
            // sleep episode, find and copy the previous sample, as that's
            // cheaper than taking a new sample.
            if (registeredThread->RacyRegisteredThread()
                    .CanDuplicateLastSampleDueToSleep()) {
              bool dup_ok = ActivePS::Buffer(lock).DuplicateLastSample(
                  info->ThreadId(), CorePS::ProcessStartTime(),
                  profiledThreadData->LastSample());
              if (dup_ok) {
                continue;
              }
            }

            AUTO_PROFILER_STATS(base_SamplerThread_Run_DoPeriodicSample);

            TimeStamp now = TimeStamp::Now();

            // Record the global profiler buffer's range start now, before
            // adding the first entry for this thread's sample.
            const uint64_t bufferRangeStart = buffer.BufferRangeStart();

            // Add the thread ID now, so we know its position in the main
            // buffer, which is used by some JS data. (DoPeriodicSample only
            // knows about the temporary local buffer.)
            const uint64_t samplePos =
                buffer.AddThreadIdEntry(registeredThread->Info()->ThreadId());
            profiledThreadData->LastSample() = Some(samplePos);

            // Also add the time, so it's always there after the thread ID, as
            // expected by the parser. (Other stack data is optional.)
            TimeDuration delta = now - CorePS::ProcessStartTime();
            buffer.AddEntry(ProfileBufferEntry::Time(delta.ToMilliseconds()));

            mSampler.SuspendAndSampleAndResumeThread(
                lock, *registeredThread, now,
                [&](const Registers& aRegs, const TimeStamp& aNow) {
                  DoPeriodicSample(lock, *registeredThread, *profiledThreadData,
                                   aRegs, samplePos, bufferRangeStart,
                                   localProfileBuffer);
                });

            // If data is complete, copy it into the global buffer.
            auto state = localBuffer.GetState();
            if (state.mClearedBlockCount != previousState.mClearedBlockCount) {
              LOG("Stack sample too big for local storage, needed %u bytes",
                  unsigned(state.mRangeEnd - previousState.mRangeEnd));
            } else if (state.mRangeEnd - previousState.mRangeEnd >=
                       *profiler_get_core_buffer().BufferLength()) {
              LOG("Stack sample too big for profiler storage, needed %u bytes",
                  unsigned(state.mRangeEnd - previousState.mRangeEnd));
            } else {
              profiler_get_core_buffer().AppendContents(localBuffer);
            }

            // Clean up for the next run.
            localBuffer.Clear();
            previousState = localBuffer.GetState();
          }
        }

#if defined(USE_LUL_STACKWALK)
        // The LUL unwind object accumulates frame statistics. Periodically we
        // should poke it to give it a chance to print those statistics.  This
        // involves doing I/O (fprintf, __android_log_print, etc.) and so
        // can't safely be done from the critical section inside
        // SuspendAndSampleAndResumeThread, which is why it is done here.
        lul::LUL* lul = CorePS::Lul(lock);
        if (lul) {
          lul->MaybeShowStats();
        }
#endif
        TimeStamp threadsSampled = TimeStamp::Now();

        {
          AUTO_PROFILER_STATS(Sampler_FulfillChunkRequests);
          ActivePS::FulfillChunkRequests(lock);
        }

        buffer.CollectOverheadStats(delta, lockAcquired - sampleStart,
                                    expiredMarkersCleaned - lockAcquired,
                                    countersSampled - expiredMarkersCleaned,
                                    threadsSampled - countersSampled);
      }
    }
    // gPSMutex is not held after this point.

    // Calculate how long a sleep to request.  After the sleep, measure how
    // long we actually slept and take the difference into account when
    // calculating the sleep interval for the next iteration.  This is an
    // attempt to keep "to schedule" in the presence of inaccuracy of the
    // actual sleep intervals.
    TimeStamp targetSleepEndTime =
        sampleStart + TimeDuration::FromMicroseconds(mIntervalMicroseconds);
    TimeStamp beforeSleep = TimeStamp::Now();
    TimeDuration targetSleepDuration = targetSleepEndTime - beforeSleep;
    double sleepTime = std::max(
        0.0, (targetSleepDuration - lastSleepOvershoot).ToMicroseconds());
    SleepMicro(static_cast<uint32_t>(sleepTime));
    sampleStart = TimeStamp::Now();
    lastSleepOvershoot =
        sampleStart - (beforeSleep + TimeDuration::FromMicroseconds(sleepTime));
  }
}

// Temporary closing namespaces from enclosing platform.cpp.
}  // namespace baseprofiler
}  // namespace mozilla

// We #include these files directly because it means those files can use
// declarations from this file trivially.  These provide target-specific
// implementations of all SamplerThread methods except Run().
#if defined(GP_OS_windows)
#  include "platform-win32.cpp"
#elif defined(GP_OS_darwin)
#  include "platform-macos.cpp"
#elif defined(GP_OS_linux) || defined(GP_OS_android) || defined(GP_OS_freebsd)
#  include "platform-linux-android.cpp"
#else
#  error "bad platform"
#endif

namespace mozilla {
namespace baseprofiler {

UniquePlatformData AllocPlatformData(BaseProfilerThreadId aThreadId) {
  return UniquePlatformData(new PlatformData(aThreadId));
}

void PlatformDataDestructor::operator()(PlatformData* aData) { delete aData; }

// END SamplerThread
////////////////////////////////////////////////////////////////////////

////////////////////////////////////////////////////////////////////////
// BEGIN externally visible functions

static uint32_t ParseFeature(const char* aFeature, bool aIsStartup) {
  if (strcmp(aFeature, "default") == 0) {
    return (aIsStartup ? (DefaultFeatures() | StartupExtraDefaultFeatures())
                       : DefaultFeatures()) &
           AvailableFeatures();
  }

#define PARSE_FEATURE_BIT(n_, str_, Name_, desc_) \
  if (strcmp(aFeature, str_) == 0) {              \
    return ProfilerFeature::Name_;                \
  }

  BASE_PROFILER_FOR_EACH_FEATURE(PARSE_FEATURE_BIT)

#undef PARSE_FEATURE_BIT

  PrintToConsole("\nUnrecognized feature \"%s\".\n\n", aFeature);
  // Since we may have an old feature we don't implement anymore, don't exit.
  PrintUsage();
  return 0;
}

uint32_t ParseFeaturesFromStringArray(const char** aFeatures,
                                      uint32_t aFeatureCount,
                                      bool aIsStartup /* = false */) {
  uint32_t features = 0;
  for (size_t i = 0; i < aFeatureCount; i++) {
    features |= ParseFeature(aFeatures[i], aIsStartup);
  }
  return features;
}

// Find the RegisteredThread for the current thread. This should only be called
// in places where TLSRegisteredThread can't be used.
static RegisteredThread* FindCurrentThreadRegisteredThread(PSLockRef aLock) {
  BaseProfilerThreadId id = profiler_current_thread_id();
  const Vector<UniquePtr<RegisteredThread>>& registeredThreads =
      CorePS::RegisteredThreads(aLock);
  for (auto& registeredThread : registeredThreads) {
    if (registeredThread->Info()->ThreadId() == id) {
      return registeredThread.get();
    }
  }

  return nullptr;
}

static ProfilingStack* locked_register_thread(PSLockRef aLock,
                                              const char* aName,
                                              void* aStackTop) {
  MOZ_RELEASE_ASSERT(CorePS::Exists());

  MOZ_ASSERT(!FindCurrentThreadRegisteredThread(aLock));

  VTUNE_REGISTER_THREAD(aName);

  if (!TLSRegisteredThread::Init(aLock)) {
    return nullptr;
  }

  RefPtr<ThreadInfo> info = new ThreadInfo(aName, profiler_current_thread_id(),
                                           profiler_is_main_thread());
  UniquePtr<RegisteredThread> registeredThread =
      MakeUnique<RegisteredThread>(info, aStackTop);

  TLSRegisteredThread::SetRegisteredThread(aLock, registeredThread.get());

  if (ActivePS::Exists(aLock) && ActivePS::ShouldProfileThread(aLock, info)) {
    registeredThread->RacyRegisteredThread().SetIsBeingProfiled(true);
    ActivePS::AddLiveProfiledThread(aLock, registeredThread.get(),
                                    MakeUnique<ProfiledThreadData>(info));
  }

  ProfilingStack* profilingStack =
      &registeredThread->RacyRegisteredThread().ProfilingStack();

  CorePS::AppendRegisteredThread(aLock, std::move(registeredThread));

  return profilingStack;
}

static void locked_profiler_start(PSLockRef aLock, PowerOfTwo32 aCapacity,
                                  double aInterval, uint32_t aFeatures,
                                  const char** aFilters, uint32_t aFilterCount,
                                  const Maybe<double>& aDuration);

static Vector<const char*> SplitAtCommas(const char* aString,
                                         UniquePtr<char[]>& aStorage) {
  size_t len = strlen(aString);
  aStorage = MakeUnique<char[]>(len + 1);
  PodCopy(aStorage.get(), aString, len + 1);

  // Iterate over all characters in aStorage and split at commas, by
  // overwriting commas with the null char.
  Vector<const char*> array;
  size_t currentElementStart = 0;
  for (size_t i = 0; i <= len; i++) {
    if (aStorage[i] == ',') {
      aStorage[i] = '\0';
    }
    if (aStorage[i] == '\0') {
      // Only add non-empty elements, otherwise ParseFeatures would later
      // complain about unrecognized features.
      if (currentElementStart != i) {
        MOZ_RELEASE_ASSERT(array.append(&aStorage[currentElementStart]));
      }
      currentElementStart = i + 1;
    }
  }
  return array;
}

static const char* get_size_suffix(const char* str) {
  const char* ptr = str;

  while (isdigit(*ptr)) {
    ptr++;
  }

  return ptr;
}

void profiler_init(void* aStackTop) {
  LOG("profiler_init");

  profiler_init_main_thread_id();

  VTUNE_INIT();

  MOZ_RELEASE_ASSERT(!CorePS::Exists());

  if (getenv("MOZ_BASE_PROFILER_HELP")) {
    PrintUsage();
    exit(0);
  }

  SharedLibraryInfo::Initialize();

  uint32_t features = DefaultFeatures() & AvailableFeatures();

  UniquePtr<char[]> filterStorage;

  Vector<const char*> filters;
  MOZ_RELEASE_ASSERT(filters.append(kMainThreadName));

  PowerOfTwo32 capacity = BASE_PROFILER_DEFAULT_ENTRIES;
  Maybe<double> duration = Nothing();
  double interval = BASE_PROFILER_DEFAULT_INTERVAL;

  {
    PSAutoLock lock;

    // We've passed the possible failure point. Instantiate CorePS, which
    // indicates that the profiler has initialized successfully.
    CorePS::Create(lock);

    Unused << locked_register_thread(lock, kMainThreadName, aStackTop);

    // Platform-specific initialization.
    PlatformInit(lock);

    // (Linux-only) We could create CorePS::mLul and read unwind info into it
    // at this point. That would match the lifetime implied by destruction of
    // it in profiler_shutdown() just below. However, that gives a big delay on
    // startup, even if no profiling is actually to be done. So, instead, it is
    // created on demand at the first call to PlatformStart().

    const char* startupEnv = getenv("MOZ_PROFILER_STARTUP");
    if (!startupEnv || startupEnv[0] == '\0' ||
        ((startupEnv[0] == '0' || startupEnv[0] == 'N' ||
          startupEnv[0] == 'n') &&
         startupEnv[1] == '\0')) {
      return;
    }

    // Hidden option to stop Base Profiler, mostly due to Talos intermittents,
    // see https://bugzilla.mozilla.org/show_bug.cgi?id=1638851#c3
    // TODO: Investigate root cause and remove this in bugs 1648324 and 1648325.
    if (getenv("MOZ_PROFILER_STARTUP_NO_BASE")) {
      return;
    }

    LOG("- MOZ_PROFILER_STARTUP is set");

    // Startup default capacity may be different.
    capacity = BASE_PROFILER_DEFAULT_STARTUP_ENTRIES;

    const char* startupCapacity = getenv("MOZ_PROFILER_STARTUP_ENTRIES");
    if (startupCapacity && startupCapacity[0] != '\0') {
      errno = 0;
      long capacityLong = strtol(startupCapacity, nullptr, 10);
      std::string_view sizeSuffix = get_size_suffix(startupCapacity);

      if (sizeSuffix == "KB") {
        capacityLong *= 1000 / scBytesPerEntry;
      } else if (sizeSuffix == "KiB") {
        capacityLong *= 1024 / scBytesPerEntry;
      } else if (sizeSuffix == "MB") {
        capacityLong *= (1000 * 1000) / scBytesPerEntry;
      } else if (sizeSuffix == "MiB") {
        capacityLong *= (1024 * 1024) / scBytesPerEntry;
      } else if (sizeSuffix == "GB") {
        capacityLong *= (1000 * 1000 * 1000) / scBytesPerEntry;
      } else if (sizeSuffix == "GiB") {
        capacityLong *= (1024 * 1024 * 1024) / scBytesPerEntry;
      } else if (!sizeSuffix.empty()) {
        PrintToConsole(
            "- MOZ_PROFILER_STARTUP_ENTRIES unit must be one of the "
            "following: KB, KiB, MB, MiB, GB, GiB");
        PrintUsage();
        exit(1);
      }

      // `long` could be 32 or 64 bits, so we force a 64-bit comparison with
      // the maximum 32-bit signed number (as more than that is clamped down to
      // 2^31 anyway).
      if (errno == 0 && capacityLong > 0 &&
          static_cast<uint64_t>(capacityLong) <=
              static_cast<uint64_t>(INT32_MAX)) {
        capacity = PowerOfTwo32(ActivePS::ClampToAllowedEntries(
            static_cast<uint32_t>(capacityLong)));
        LOG("- MOZ_PROFILER_STARTUP_ENTRIES = %u", unsigned(capacity.Value()));
      } else {
        PrintToConsole("- MOZ_PROFILER_STARTUP_ENTRIES not a valid integer: %s",
                       startupCapacity);
        PrintUsage();
        exit(1);
      }
    }

    const char* startupDuration = getenv("MOZ_PROFILER_STARTUP_DURATION");
    if (startupDuration && startupDuration[0] != '\0') {
      // The duration is a floating point number. Use StringToDouble rather than
      // strtod, so that "." is used as the decimal separator regardless of OS
      // locale.
      auto durationVal = StringToDouble(std::string(startupDuration));
      if (durationVal && *durationVal >= 0.0) {
        if (*durationVal > 0.0) {
          duration = Some(*durationVal);
        }
        LOG("- MOZ_PROFILER_STARTUP_DURATION = %f", *durationVal);
      } else {
        PrintToConsole("- MOZ_PROFILER_STARTUP_DURATION not a valid float: %s",
                       startupDuration);
        PrintUsage();
        exit(1);
      }
    }

    const char* startupInterval = getenv("MOZ_PROFILER_STARTUP_INTERVAL");
    if (startupInterval && startupInterval[0] != '\0') {
      // The interval is a floating point number. Use StringToDouble rather than
      // strtod, so that "." is used as the decimal separator regardless of OS
      // locale.
      auto intervalValue = StringToDouble(MakeStringSpan(startupInterval));
      if (intervalValue && *intervalValue > 0.0 && *intervalValue <= 1000.0) {
        interval = *intervalValue;
        LOG("- MOZ_PROFILER_STARTUP_INTERVAL = %f", interval);
      } else {
        PrintToConsole("- MOZ_PROFILER_STARTUP_INTERVAL not a valid float: %s",
                       startupInterval);
        PrintUsage();
        exit(1);
      }
    }

    features |= StartupExtraDefaultFeatures() & AvailableFeatures();

    const char* startupFeaturesBitfield =
        getenv("MOZ_PROFILER_STARTUP_FEATURES_BITFIELD");
    if (startupFeaturesBitfield && startupFeaturesBitfield[0] != '\0') {
      errno = 0;
      features = strtol(startupFeaturesBitfield, nullptr, 10);
      if (errno == 0) {
        LOG("- MOZ_PROFILER_STARTUP_FEATURES_BITFIELD = %d", features);
      } else {
        PrintToConsole(
            "- MOZ_PROFILER_STARTUP_FEATURES_BITFIELD not a valid integer: %s",
            startupFeaturesBitfield);
        PrintUsage();
        exit(1);
      }
    } else {
      const char* startupFeatures = getenv("MOZ_PROFILER_STARTUP_FEATURES");
      if (startupFeatures) {
        // Interpret startupFeatures as a list of feature strings, separated by
        // commas.
        UniquePtr<char[]> featureStringStorage;
        Vector<const char*> featureStringArray =
            SplitAtCommas(startupFeatures, featureStringStorage);
        features = ParseFeaturesFromStringArray(featureStringArray.begin(),
                                                featureStringArray.length(),
                                                /* aIsStartup */ true);
        LOG("- MOZ_PROFILER_STARTUP_FEATURES = %d", features);
      }
    }

    const char* startupFilters = getenv("MOZ_PROFILER_STARTUP_FILTERS");
    if (startupFilters && startupFilters[0] != '\0') {
      filters = SplitAtCommas(startupFilters, filterStorage);
      LOG("- MOZ_PROFILER_STARTUP_FILTERS = %s", startupFilters);

      if (mozilla::profiler::detail::FiltersExcludePid(filters)) {
        LOG(" -> This process is excluded and won't be profiled");
        return;
      }
    }

    locked_profiler_start(lock, capacity, interval, features, filters.begin(),
                          filters.length(), duration);
  }

  // TODO: Install memory counter if it is possible from mozglue.
  // #if defined(MOZ_REPLACE_MALLOC) && defined(MOZ_PROFILER_MEMORY)
  //   // start counting memory allocations (outside of lock because this may
  //   call
  //   // profiler_add_sampled_counter which would attempt to take the lock.)
  //   mozilla::profiler::install_memory_counter(true);
  // #endif
}

static void locked_profiler_save_profile_to_file(PSLockRef aLock,
                                                 const char* aFilename,
                                                 bool aIsShuttingDown);

static SamplerThread* locked_profiler_stop(PSLockRef aLock);

void profiler_shutdown() {
  LOG("profiler_shutdown");

  VTUNE_SHUTDOWN();

  MOZ_RELEASE_ASSERT(profiler_is_main_thread());
  MOZ_RELEASE_ASSERT(CorePS::Exists());

  // If the profiler is active we must get a handle to the SamplerThread before
  // ActivePS is destroyed, in order to delete it.
  SamplerThread* samplerThread = nullptr;
  {
    PSAutoLock lock;

    // Save the profile on shutdown if requested.
    if (ActivePS::Exists(lock)) {
      const char* filename = getenv("MOZ_PROFILER_SHUTDOWN");
      if (filename && filename[0] != '\0') {
        locked_profiler_save_profile_to_file(lock, filename,
                                             /* aIsShuttingDown */ true);
      }

      samplerThread = locked_profiler_stop(lock);
    }

    CorePS::Destroy(lock);

    // We just destroyed CorePS and the ThreadInfos it contains, so we can
    // clear this thread's TLSRegisteredThread.
    TLSRegisteredThread::SetRegisteredThread(lock, nullptr);
  }

  // We do these operations with gPSMutex unlocked. The comments in
  // profiler_stop() explain why.
  if (samplerThread) {
    delete samplerThread;
  }
}

static bool WriteProfileToJSONWriter(SpliceableChunkedJSONWriter& aWriter,
                                     double aSinceTime, bool aIsShuttingDown,
                                     bool aOnlyThreads = false) {
  LOG("WriteProfileToJSONWriter");

  MOZ_RELEASE_ASSERT(CorePS::Exists());

  if (!aOnlyThreads) {
    aWriter.Start();
    {
      if (!profiler_stream_json_for_this_process(
              aWriter, aSinceTime, aIsShuttingDown, aOnlyThreads)) {
        return false;
      }

      // Don't include profiles from other processes because this is a
      // synchronous function.
      aWriter.StartArrayProperty("processes");
      aWriter.EndArray();
    }
    aWriter.End();
  } else {
    aWriter.StartBareList();
    if (!profiler_stream_json_for_this_process(aWriter, aSinceTime,
                                               aIsShuttingDown, aOnlyThreads)) {
      return false;
    }
    aWriter.EndBareList();
  }
  return true;
}

void profiler_set_process_name(const std::string& aProcessName,
                               const std::string* aETLDplus1) {
  LOG("profiler_set_process_name(\"%s\", \"%s\")", aProcessName.c_str(),
      aETLDplus1 ? aETLDplus1->c_str() : "<none>");
  PSAutoLock lock;
  CorePS::SetProcessName(lock, aProcessName);
  if (aETLDplus1) {
    CorePS::SetETLDplus1(lock, *aETLDplus1);
  }
}

UniquePtr<char[]> profiler_get_profile(double aSinceTime, bool aIsShuttingDown,
                                       bool aOnlyThreads) {
  LOG("profiler_get_profile");

  SpliceableChunkedJSONWriter b{FailureLatchInfallibleSource::Singleton()};
  if (!WriteProfileToJSONWriter(b, aSinceTime, aIsShuttingDown, aOnlyThreads)) {
    return nullptr;
  }
  return b.ChunkedWriteFunc().CopyData();
}

void profiler_get_start_params(int* aCapacity, Maybe<double>* aDuration,
                               double* aInterval, uint32_t* aFeatures,
                               Vector<const char*>* aFilters) {
  MOZ_RELEASE_ASSERT(CorePS::Exists());

  if (!aCapacity || !aDuration || !aInterval || !aFeatures || !aFilters) {
    return;
  }

  PSAutoLock lock;

  if (!ActivePS::Exists(lock)) {
    *aCapacity = 0;
    *aDuration = Nothing();
    *aInterval = 0;
    *aFeatures = 0;
    aFilters->clear();
    return;
  }

  *aCapacity = ActivePS::Capacity(lock).Value();
  *aDuration = ActivePS::Duration(lock);
  *aInterval = ActivePS::Interval(lock);
  *aFeatures = ActivePS::Features(lock);

  const Vector<std::string>& filters = ActivePS::Filters(lock);
  MOZ_ALWAYS_TRUE(aFilters->resize(filters.length()));
  for (uint32_t i = 0; i < filters.length(); ++i) {
    (*aFilters)[i] = filters[i].c_str();
  }
}

void GetProfilerEnvVarsForChildProcess(
    std::function<void(const char* key, const char* value)>&& aSetEnv) {
  MOZ_RELEASE_ASSERT(CorePS::Exists());

  PSAutoLock lock;

  if (!ActivePS::Exists(lock)) {
    aSetEnv("MOZ_PROFILER_STARTUP", "");
    return;
  }

  aSetEnv("MOZ_PROFILER_STARTUP", "1");
  auto capacityString =
      Smprintf("%u", unsigned(ActivePS::Capacity(lock).Value()));
  aSetEnv("MOZ_PROFILER_STARTUP_ENTRIES", capacityString.get());

  // Use AppendFloat instead of Smprintf with %f because the decimal
  // separator used by %f is locale-dependent. But the string we produce needs
  // to be parseable by strtod, which only accepts the period character as a
  // decimal separator. AppendFloat always uses the period character.
  std::string intervalString = std::to_string(ActivePS::Interval(lock));
  aSetEnv("MOZ_PROFILER_STARTUP_INTERVAL", intervalString.c_str());

  auto featuresString = Smprintf("%d", ActivePS::Features(lock));
  aSetEnv("MOZ_PROFILER_STARTUP_FEATURES_BITFIELD", featuresString.get());

  std::string filtersString;
  const Vector<std::string>& filters = ActivePS::Filters(lock);
  for (uint32_t i = 0; i < filters.length(); ++i) {
    filtersString += filters[i];
    if (i != filters.length() - 1) {
      filtersString += ",";
    }
  }
  aSetEnv("MOZ_PROFILER_STARTUP_FILTERS", filtersString.c_str());
}

void profiler_received_exit_profile(const std::string& aExitProfile) {
  MOZ_RELEASE_ASSERT(CorePS::Exists());
  PSAutoLock lock;
  if (!ActivePS::Exists(lock)) {
    return;
  }
  ActivePS::AddExitProfile(lock, aExitProfile);
}

Vector<std::string> profiler_move_exit_profiles() {
  MOZ_RELEASE_ASSERT(CorePS::Exists());
  PSAutoLock lock;
  Vector<std::string> profiles;
  if (ActivePS::Exists(lock)) {
    profiles = ActivePS::MoveExitProfiles(lock);
  }
  return profiles;
}

static void locked_profiler_save_profile_to_file(PSLockRef aLock,
                                                 const char* aFilename,
                                                 bool aIsShuttingDown = false) {
  LOG("locked_profiler_save_profile_to_file(%s)", aFilename);

  MOZ_RELEASE_ASSERT(CorePS::Exists() && ActivePS::Exists(aLock));

  std::ofstream stream;
  stream.open(aFilename);
  if (stream.is_open()) {
    OStreamJSONWriteFunc jw(stream);
    SpliceableJSONWriter w(jw, FailureLatchInfallibleSource::Singleton());
    w.Start();
    {
      locked_profiler_stream_json_for_this_process(aLock, w, /* sinceTime */ 0,
                                                   aIsShuttingDown);

      w.StartArrayProperty("processes");
      Vector<std::string> exitProfiles = ActivePS::MoveExitProfiles(aLock);
      for (auto& exitProfile : exitProfiles) {
        if (!exitProfile.empty()) {
          w.Splice(exitProfile);
        }
      }
      w.EndArray();
    }
    w.End();

    stream.close();
  }
}

void baseprofiler_save_profile_to_file(const char* aFilename) {
  LOG("baseprofiler_save_profile_to_file(%s)", aFilename);

  MOZ_RELEASE_ASSERT(CorePS::Exists());

  PSAutoLock lock;

  if (!ActivePS::Exists(lock)) {
    return;
  }

  locked_profiler_save_profile_to_file(lock, aFilename);
}

uint32_t profiler_get_available_features() {
  MOZ_RELEASE_ASSERT(CorePS::Exists());
  return AvailableFeatures();
}

Maybe<ProfilerBufferInfo> profiler_get_buffer_info() {
  MOZ_RELEASE_ASSERT(CorePS::Exists());

  PSAutoLock lock;

  if (!ActivePS::Exists(lock)) {
    return Nothing();
  }

  return Some(ActivePS::Buffer(lock).GetProfilerBufferInfo());
}

// This basically duplicates AutoProfilerLabel's constructor.
static void* MozGlueBaseLabelEnter(const char* aLabel,
                                   const char* aDynamicString, void* aSp) {
  ProfilingStack* profilingStack = AutoProfilerLabel::sProfilingStack.get();
  if (profilingStack) {
    profilingStack->pushLabelFrame(aLabel, aDynamicString, aSp,
                                   ProfilingCategoryPair::OTHER);
  }
  return profilingStack;
}

// This basically duplicates AutoProfilerLabel's destructor.
static void MozGlueBaseLabelExit(void* sProfilingStack) {
  if (sProfilingStack) {
    reinterpret_cast<ProfilingStack*>(sProfilingStack)->pop();
  }
}

static void locked_profiler_start(PSLockRef aLock, PowerOfTwo32 aCapacity,
                                  double aInterval, uint32_t aFeatures,
                                  const char** aFilters, uint32_t aFilterCount,
                                  const Maybe<double>& aDuration) {
  const TimeStamp profilingStartTime = TimeStamp::Now();

  if (LOG_TEST) {
    LOG("locked_profiler_start");
    LOG("- capacity  = %d", int(aCapacity.Value()));
    LOG("- duration  = %.2f", aDuration ? *aDuration : -1);
    LOG("- interval = %.2f", aInterval);

#define LOG_FEATURE(n_, str_, Name_, desc_)     \
  if (ProfilerFeature::Has##Name_(aFeatures)) { \
    LOG("- feature  = %s", str_);               \
  }

    BASE_PROFILER_FOR_EACH_FEATURE(LOG_FEATURE)

#undef LOG_FEATURE

    for (uint32_t i = 0; i < aFilterCount; i++) {
      LOG("- threads  = %s", aFilters[i]);
    }
  }

  MOZ_RELEASE_ASSERT(CorePS::Exists() && !ActivePS::Exists(aLock));

  mozilla::base_profiler_markers_detail::EnsureBufferForMainThreadAddMarker();

#if defined(GP_PLAT_amd64_windows)
  InitializeWin64ProfilerHooks();
#endif

  // Fall back to the default values if the passed-in values are unreasonable.
  // We want to be able to store at least one full stack.
  // TODO: Review magic numbers.
  PowerOfTwo32 capacity =
      (aCapacity.Value() >=
       ProfileBufferChunkManager::scExpectedMaximumStackSize / scBytesPerEntry)
          ? aCapacity
          : BASE_PROFILER_DEFAULT_ENTRIES;
  Maybe<double> duration = aDuration;

  if (aDuration && *aDuration <= 0) {
    duration = Nothing();
  }
  double interval = aInterval > 0 ? aInterval : BASE_PROFILER_DEFAULT_INTERVAL;

  ActivePS::Create(aLock, profilingStartTime, capacity, interval, aFeatures,
                   aFilters, aFilterCount, duration);

  // Set up profiling for each registered thread, if appropriate.
  const Vector<UniquePtr<RegisteredThread>>& registeredThreads =
      CorePS::RegisteredThreads(aLock);
  for (auto& registeredThread : registeredThreads) {
    RefPtr<ThreadInfo> info = registeredThread->Info();

    if (ActivePS::ShouldProfileThread(aLock, info)) {
      registeredThread->RacyRegisteredThread().SetIsBeingProfiled(true);
      ActivePS::AddLiveProfiledThread(aLock, registeredThread.get(),
                                      MakeUnique<ProfiledThreadData>(info));
      registeredThread->RacyRegisteredThread().ReinitializeOnResume();
    }
  }

  // Setup support for pushing/popping labels in mozglue.
  RegisterProfilerLabelEnterExit(MozGlueBaseLabelEnter, MozGlueBaseLabelExit);

  // At the very end, set up RacyFeatures.
  RacyFeatures::SetActive(ActivePS::Features(aLock));
}

void profiler_start(PowerOfTwo32 aCapacity, double aInterval,
                    uint32_t aFeatures, const char** aFilters,
                    uint32_t aFilterCount, const Maybe<double>& aDuration) {
  LOG("profiler_start");

  SamplerThread* samplerThread = nullptr;
  {
    PSAutoLock lock;

    // Initialize if necessary.
    if (!CorePS::Exists()) {
      profiler_init(nullptr);
    }

    // Reset the current state if the profiler is running.
    if (ActivePS::Exists(lock)) {
      samplerThread = locked_profiler_stop(lock);
    }

    locked_profiler_start(lock, aCapacity, aInterval, aFeatures, aFilters,
                          aFilterCount, aDuration);
  }

  // TODO: Install memory counter if it is possible from mozglue.
  // #if defined(MOZ_REPLACE_MALLOC) && defined(MOZ_PROFILER_MEMORY)
  //   // start counting memory allocations (outside of lock because this may
  //   call
  //   // profiler_add_sampled_counter which would attempt to take the lock.)
  //   mozilla::profiler::install_memory_counter(true);
  // #endif

  // We do these operations with gPSMutex unlocked. The comments in
  // profiler_stop() explain why.
  if (samplerThread) {
    delete samplerThread;
  }
}

void profiler_ensure_started(PowerOfTwo32 aCapacity, double aInterval,
                             uint32_t aFeatures, const char** aFilters,
                             uint32_t aFilterCount,
                             const Maybe<double>& aDuration) {
  LOG("profiler_ensure_started");

  // bool startedProfiler = false; (See TODO below)
  SamplerThread* samplerThread = nullptr;
  {
    PSAutoLock lock;

    // Initialize if necessary.
    if (!CorePS::Exists()) {
      profiler_init(nullptr);
    }

    if (ActivePS::Exists(lock)) {
      // The profiler is active.
      if (!ActivePS::Equals(lock, aCapacity, aDuration, aInterval, aFeatures,
                            aFilters, aFilterCount)) {
        // Stop and restart with different settings.
        samplerThread = locked_profiler_stop(lock);
        locked_profiler_start(lock, aCapacity, aInterval, aFeatures, aFilters,
                              aFilterCount, aDuration);
        // startedProfiler = true; (See TODO below)
      }
    } else {
      // The profiler is stopped.
      locked_profiler_start(lock, aCapacity, aInterval, aFeatures, aFilters,
                            aFilterCount, aDuration);
      // startedProfiler = true; (See TODO below)
    }
  }

  // TODO: Install memory counter if it is possible from mozglue.
  // #if defined(MOZ_REPLACE_MALLOC) && defined(MOZ_PROFILER_MEMORY)
  //   // start counting memory allocations (outside of lock because this may
  //   // call profiler_add_sampled_counter which would attempt to take the
  //   // lock.)
  //   mozilla::profiler::install_memory_counter(true);
  // #endif

  // We do these operations with gPSMutex unlocked. The comments in
  // profiler_stop() explain why.
  if (samplerThread) {
    delete samplerThread;
  }
}

[[nodiscard]] static SamplerThread* locked_profiler_stop(PSLockRef aLock) {
  LOG("locked_profiler_stop");

  MOZ_RELEASE_ASSERT(CorePS::Exists() && ActivePS::Exists(aLock));

  // At the very start, clear RacyFeatures.
  RacyFeatures::SetInactive();

  // TODO: Uninstall memory counter if it is possible from mozglue.
  // #if defined(MOZ_REPLACE_MALLOC) && defined(MOZ_PROFILER_MEMORY)
  //   mozilla::profiler::install_memory_counter(false);
  // #endif

  // Remove support for pushing/popping labels in mozglue.
  RegisterProfilerLabelEnterExit(nullptr, nullptr);

  // Stop sampling live threads.
  const Vector<LiveProfiledThreadData>& liveProfiledThreads =
      ActivePS::LiveProfiledThreads(aLock);
  for (auto& thread : liveProfiledThreads) {
    RegisteredThread* registeredThread = thread.mRegisteredThread;
    registeredThread->RacyRegisteredThread().SetIsBeingProfiled(false);
  }

  // The Stop() call doesn't actually stop Run(); that happens in this
  // function's caller when the sampler thread is destroyed. Stop() just gives
  // the SamplerThread a chance to do some cleanup with gPSMutex locked.
  SamplerThread* samplerThread = ActivePS::Destroy(aLock);
  samplerThread->Stop(aLock);

  mozilla::base_profiler_markers_detail::ReleaseBufferForMainThreadAddMarker();

  return samplerThread;
}

void profiler_stop() {
  LOG("profiler_stop");

  MOZ_RELEASE_ASSERT(CorePS::Exists());

  SamplerThread* samplerThread;
  {
    PSAutoLock lock;

    if (!ActivePS::Exists(lock)) {
      return;
    }

    samplerThread = locked_profiler_stop(lock);
  }

  // We delete with gPSMutex unlocked. Otherwise we would get a deadlock: we
  // would be waiting here with gPSMutex locked for SamplerThread::Run() to
  // return so the join operation within the destructor can complete, but Run()
  // needs to lock gPSMutex to return.
  //
  // Because this call occurs with gPSMutex unlocked, it -- including the final
  // iteration of Run()'s loop -- must be able detect deactivation and return
  // in a way that's safe with respect to other gPSMutex-locking operations
  // that may have occurred in the meantime.
  delete samplerThread;
}

bool profiler_is_paused() {
  MOZ_RELEASE_ASSERT(CorePS::Exists());

  PSAutoLock lock;

  if (!ActivePS::Exists(lock)) {
    return false;
  }

  return ActivePS::IsPaused(lock);
}

void profiler_pause() {
  LOG("profiler_pause");

  MOZ_RELEASE_ASSERT(CorePS::Exists());

  {
    PSAutoLock lock;

    if (!ActivePS::Exists(lock)) {
      return;
    }

    RacyFeatures::SetPaused();
    ActivePS::SetIsPaused(lock, true);
    ActivePS::Buffer(lock).AddEntry(ProfileBufferEntry::Pause(profiler_time()));
  }
}

void profiler_resume() {
  LOG("profiler_resume");

  MOZ_RELEASE_ASSERT(CorePS::Exists());

  {
    PSAutoLock lock;

    if (!ActivePS::Exists(lock)) {
      return;
    }

    ActivePS::Buffer(lock).AddEntry(
        ProfileBufferEntry::Resume(profiler_time()));
    ActivePS::SetIsPaused(lock, false);
    RacyFeatures::SetUnpaused();
  }
}

bool profiler_is_sampling_paused() {
  MOZ_RELEASE_ASSERT(CorePS::Exists());

  PSAutoLock lock;

  if (!ActivePS::Exists(lock)) {
    return false;
  }

  return ActivePS::IsSamplingPaused(lock);
}

void profiler_pause_sampling() {
  LOG("profiler_pause_sampling");

  MOZ_RELEASE_ASSERT(CorePS::Exists());

  {
    PSAutoLock lock;

    if (!ActivePS::Exists(lock)) {
      return;
    }

    RacyFeatures::SetSamplingPaused();
    ActivePS::SetIsSamplingPaused(lock, true);
    ActivePS::Buffer(lock).AddEntry(
        ProfileBufferEntry::PauseSampling(profiler_time()));
  }
}

void profiler_resume_sampling() {
  LOG("profiler_resume_sampling");

  MOZ_RELEASE_ASSERT(CorePS::Exists());

  {
    PSAutoLock lock;

    if (!ActivePS::Exists(lock)) {
      return;
    }

    ActivePS::Buffer(lock).AddEntry(
        ProfileBufferEntry::ResumeSampling(profiler_time()));
    ActivePS::SetIsSamplingPaused(lock, false);
    RacyFeatures::SetSamplingUnpaused();
  }
}

bool profiler_feature_active(uint32_t aFeature) {
  // This function runs both on and off the main thread.

  MOZ_RELEASE_ASSERT(CorePS::Exists());

  // This function is hot enough that we use RacyFeatures, not ActivePS.
  return RacyFeatures::IsActiveWithFeature(aFeature);
}

void profiler_add_sampled_counter(BaseProfilerCount* aCounter) {
  DEBUG_LOG("profiler_add_sampled_counter(%s)", aCounter->mLabel);
  PSAutoLock lock;
  CorePS::AppendCounter(lock, aCounter);
}

void profiler_remove_sampled_counter(BaseProfilerCount* aCounter) {
  DEBUG_LOG("profiler_remove_sampled_counter(%s)", aCounter->mLabel);
  PSAutoLock lock;
  // Note: we don't enforce a final sample, though we could do so if the
  // profiler was active
  CorePS::RemoveCounter(lock, aCounter);
}

ProfilingStack* profiler_register_thread(const char* aName,
                                         void* aGuessStackTop) {
  DEBUG_LOG("profiler_register_thread(%s)", aName);

  MOZ_RELEASE_ASSERT(CorePS::Exists());

  PSAutoLock lock;

  if (RegisteredThread* thread = FindCurrentThreadRegisteredThread(lock);
      thread) {
    LOG("profiler_register_thread(%s) - thread %" PRIu64
        " already registered as %s",
        aName, uint64_t(profiler_current_thread_id().ToNumber()),
        thread->Info()->Name());
    // TODO: Use new name. This is currently not possible because the
    // RegisteredThread's ThreadInfo cannot be changed.
    // In the meantime, we record a marker that could be used in the frontend.
    std::string text("Thread ");
    text += std::to_string(profiler_current_thread_id().ToNumber());
    text += " \"";
    text += thread->Info()->Name();
    text += "\" attempted to re-register as \"";
    text += aName;
    text += "\"";
    BASE_PROFILER_MARKER_TEXT("profiler_register_thread again", OTHER_Profiling,
                              MarkerThreadId::MainThread(), text);

    return &thread->RacyRegisteredThread().ProfilingStack();
  }

  void* stackTop = GetStackTop(aGuessStackTop);
  return locked_register_thread(lock, aName, stackTop);
}

void profiler_unregister_thread() {
  if (!CorePS::Exists()) {
    // This function can be called after the main thread has already shut down.
    return;
  }

  PSAutoLock lock;

  RegisteredThread* registeredThread = FindCurrentThreadRegisteredThread(lock);
  MOZ_RELEASE_ASSERT(registeredThread ==
                     TLSRegisteredThread::RegisteredThread(lock));
  if (registeredThread) {
    RefPtr<ThreadInfo> info = registeredThread->Info();

    DEBUG_LOG("profiler_unregister_thread: %s", info->Name());

    if (ActivePS::Exists(lock)) {
      ActivePS::UnregisterThread(lock, registeredThread);
    }

    // Clear the pointer to the RegisteredThread object that we're about to
    // destroy.
    TLSRegisteredThread::SetRegisteredThread(lock, nullptr);

    // Remove the thread from the list of registered threads. This deletes the
    // registeredThread object.
    CorePS::RemoveRegisteredThread(lock, registeredThread);
  } else {
    LOG("profiler_unregister_thread() - thread %" PRIu64
        " already unregistered",
        uint64_t(profiler_current_thread_id().ToNumber()));
    // We cannot record a marker on this thread because it was already
    // unregistered. Send it to the main thread (unless this *is* already the
    // main thread, which has been unregistered); this may be useful to catch
    // mismatched register/unregister pairs in Firefox.
    if (BaseProfilerThreadId tid = profiler_current_thread_id();
        tid != profiler_main_thread_id()) {
      BASE_PROFILER_MARKER_TEXT(
          "profiler_unregister_thread again", OTHER_Profiling,
          MarkerThreadId::MainThread(),
          std::to_string(profiler_current_thread_id().ToNumber()));
    }
    // There are two ways FindCurrentThreadRegisteredThread() might have failed.
    //
    // - TLSRegisteredThread::Init() failed in locked_register_thread().
    //
    // - We've already called profiler_unregister_thread() for this thread.
    //   (Whether or not it should, this does happen in practice.)
    //
    // Either way, TLSRegisteredThread should be empty.
    MOZ_RELEASE_ASSERT(!TLSRegisteredThread::RegisteredThread(lock));
  }
}

void profiler_register_page(uint64_t aTabID, uint64_t aInnerWindowID,
                            const std::string& aUrl,
                            uint64_t aEmbedderInnerWindowID) {
  DEBUG_LOG("profiler_register_page(%" PRIu64 ", %" PRIu64 ", %s, %" PRIu64 ")",
            aTabID, aInnerWindowID, aUrl.c_str(), aEmbedderInnerWindowID);

  MOZ_RELEASE_ASSERT(CorePS::Exists());

  PSAutoLock lock;

  // When a Browsing context is first loaded, the first url loaded in it will be
  // about:blank. Because of that, this call keeps the first non-about:blank
  // registration of window and discards the previous one.
  RefPtr<PageInformation> pageInfo =
      new PageInformation(aTabID, aInnerWindowID, aUrl, aEmbedderInnerWindowID);
  CorePS::AppendRegisteredPage(lock, std::move(pageInfo));

  // After appending the given page to CorePS, look for the expired
  // pages and remove them if there are any.
  if (ActivePS::Exists(lock)) {
    ActivePS::DiscardExpiredPages(lock);
  }
}

void profiler_unregister_page(uint64_t aRegisteredInnerWindowID) {
  if (!CorePS::Exists()) {
    // This function can be called after the main thread has already shut down.
    return;
  }

  PSAutoLock lock;

  // During unregistration, if the profiler is active, we have to keep the
  // page information since there may be some markers associated with the given
  // page. But if profiler is not active. we have no reason to keep the
  // page information here because there can't be any marker associated with it.
  if (ActivePS::Exists(lock)) {
    ActivePS::UnregisterPage(lock, aRegisteredInnerWindowID);
  } else {
    CorePS::RemoveRegisteredPage(lock, aRegisteredInnerWindowID);
  }
}

void profiler_clear_all_pages() {
  if (!CorePS::Exists()) {
    // This function can be called after the main thread has already shut down.
    return;
  }

  {
    PSAutoLock lock;
    CorePS::ClearRegisteredPages(lock);
    if (ActivePS::Exists(lock)) {
      ActivePS::ClearUnregisteredPages(lock);
    }
  }
}

void profiler_thread_sleep() {
  // This function runs both on and off the main thread.

  MOZ_RELEASE_ASSERT(CorePS::Exists());

  RacyRegisteredThread* racyRegisteredThread =
      TLSRegisteredThread::RacyRegisteredThread();
  if (!racyRegisteredThread) {
    return;
  }

  racyRegisteredThread->SetSleeping();
}

void profiler_thread_wake() {
  // This function runs both on and off the main thread.

  MOZ_RELEASE_ASSERT(CorePS::Exists());

  RacyRegisteredThread* racyRegisteredThread =
      TLSRegisteredThread::RacyRegisteredThread();
  if (!racyRegisteredThread) {
    return;
  }

  racyRegisteredThread->SetAwake();
}

bool detail::IsThreadBeingProfiled() {
  MOZ_RELEASE_ASSERT(CorePS::Exists());

  const RacyRegisteredThread* racyRegisteredThread =
      TLSRegisteredThread::RacyRegisteredThread();
  return racyRegisteredThread && racyRegisteredThread->IsBeingProfiled();
}

bool profiler_thread_is_sleeping() {
  MOZ_RELEASE_ASSERT(profiler_is_main_thread());
  MOZ_RELEASE_ASSERT(CorePS::Exists());

  RacyRegisteredThread* racyRegisteredThread =
      TLSRegisteredThread::RacyRegisteredThread();
  if (!racyRegisteredThread) {
    return false;
  }
  return racyRegisteredThread->IsSleeping();
}

double profiler_time() {
  MOZ_RELEASE_ASSERT(CorePS::Exists());

  TimeDuration delta = TimeStamp::Now() - CorePS::ProcessStartTime();
  return delta.ToMilliseconds();
}

bool profiler_capture_backtrace_into(ProfileChunkedBuffer& aChunkedBuffer,
                                     StackCaptureOptions aCaptureOptions) {
  MOZ_RELEASE_ASSERT(CorePS::Exists());

  PSAutoLock lock;

  if (!ActivePS::Exists(lock) ||
      aCaptureOptions == StackCaptureOptions::NoStack) {
    return false;
  }

  RegisteredThread* registeredThread =
      TLSRegisteredThread::RegisteredThread(lock);
  if (!registeredThread) {
    MOZ_ASSERT(registeredThread);
    return false;
  }

  ProfileBuffer profileBuffer(aChunkedBuffer);

  Registers regs;
#if defined(HAVE_NATIVE_UNWIND)
  regs.SyncPopulate();
#else
  regs.Clear();
#endif

  DoSyncSample(lock, *registeredThread, TimeStamp::Now(), regs, profileBuffer,
               aCaptureOptions);

  return true;
}

UniquePtr<ProfileChunkedBuffer> profiler_capture_backtrace() {
  MOZ_RELEASE_ASSERT(CorePS::Exists());
  AUTO_BASE_PROFILER_LABEL("baseprofiler::profiler_capture_backtrace",
                           PROFILER);

  // Quick is-active check before allocating a buffer.
  if (!profiler_is_active()) {
    return nullptr;
  }

  auto buffer = MakeUnique<ProfileChunkedBuffer>(
      ProfileChunkedBuffer::ThreadSafety::WithoutMutex,
      MakeUnique<ProfileBufferChunkManagerSingle>(
          ProfileBufferChunkManager::scExpectedMaximumStackSize));

  if (!profiler_capture_backtrace_into(*buffer, StackCaptureOptions::Full)) {
    return nullptr;
  }

  return buffer;
}

UniqueProfilerBacktrace profiler_get_backtrace() {
  UniquePtr<ProfileChunkedBuffer> buffer = profiler_capture_backtrace();

  if (!buffer) {
    return nullptr;
  }

  return UniqueProfilerBacktrace(
      new ProfilerBacktrace("SyncProfile", std::move(buffer)));
}

void ProfilerBacktraceDestructor::operator()(ProfilerBacktrace* aBacktrace) {
  delete aBacktrace;
}

bool profiler_is_locked_on_current_thread() {
  // This function is used to help users avoid calling `profiler_...` functions
  // when the profiler may already have a lock in place, which would prevent a
  // 2nd recursive lock (resulting in a crash or a never-ending wait).
  // So we must return `true` for any of:
  // - The main profiler mutex, used by most functions, and/or
  // - The buffer mutex, used directly in some functions without locking the
  //   main mutex, e.g., marker-related functions.
  return PSAutoLock::IsLockedOnCurrentThread() ||
         profiler_get_core_buffer().IsThreadSafeAndLockedOnCurrentThread();
}

// This is a simplified version of profiler_add_marker that can be easily passed
// into the JS engine.
void profiler_add_js_marker(const char* aMarkerName, const char* aMarkerText) {
  BASE_PROFILER_MARKER_TEXT(
      ProfilerString8View::WrapNullTerminatedString(aMarkerName), JS, {},
      ProfilerString8View::WrapNullTerminatedString(aMarkerText));
}

// NOTE: aCollector's methods will be called while the target thread is paused.
// Doing things in those methods like allocating -- which may try to claim
// locks -- is a surefire way to deadlock.
void profiler_suspend_and_sample_thread(BaseProfilerThreadId aThreadId,
                                        uint32_t aFeatures,
                                        ProfilerStackCollector& aCollector,
                                        bool aSampleNative /* = true */) {
  const bool isSynchronous = [&aThreadId]() {
    const BaseProfilerThreadId currentThreadId = profiler_current_thread_id();
    if (!aThreadId.IsSpecified()) {
      aThreadId = currentThreadId;
      return true;
    }
    return aThreadId == currentThreadId;
  }();

  // Lock the profiler mutex
  PSAutoLock lock;

  const Vector<UniquePtr<RegisteredThread>>& registeredThreads =
      CorePS::RegisteredThreads(lock);
  for (auto& thread : registeredThreads) {
    RefPtr<ThreadInfo> info = thread->Info();
    RegisteredThread& registeredThread = *thread.get();

    if (info->ThreadId() == aThreadId) {
      if (info->IsMainThread()) {
        aCollector.SetIsMainThread();
      }

      // Allocate the space for the native stack
      NativeStack nativeStack;

      auto collectStack = [&](const Registers& aRegs, const TimeStamp& aNow) {
      // The target thread is now suspended. Collect a native
      // backtrace, and call the callback.
#if defined(HAVE_FASTINIT_NATIVE_UNWIND)
        if (aSampleNative) {
          // We can only use FramePointerStackWalk or MozStackWalk from
          // suspend_and_sample_thread as other stackwalking methods may not be
          // initialized.
#  if defined(USE_FRAME_POINTER_STACK_WALK)
          DoFramePointerBacktrace(lock, registeredThread, aRegs, nativeStack);
#  elif defined(USE_MOZ_STACK_WALK)
          DoMozStackWalkBacktrace(lock, registeredThread, aRegs, nativeStack);
#  else
#    error "Invalid configuration"
#  endif

          MergeStacks(aFeatures, isSynchronous, registeredThread, aRegs,
                      nativeStack, aCollector);
        } else
#endif
        {
          MergeStacks(aFeatures, isSynchronous, registeredThread, aRegs,
                      nativeStack, aCollector);

          aCollector.CollectNativeLeafAddr((void*)aRegs.mPC);
        }
      };

      if (isSynchronous) {
        // Sampling the current thread, do NOT suspend it!
        Registers regs;
#if defined(HAVE_NATIVE_UNWIND)
        regs.SyncPopulate();
#else
        regs.Clear();
#endif
        collectStack(regs, TimeStamp::Now());
      } else {
        // Suspend, sample, and then resume the target thread.
        Sampler sampler(lock);
        TimeStamp now = TimeStamp::Now();
        sampler.SuspendAndSampleAndResumeThread(lock, registeredThread, now,
                                                collectStack);

        // NOTE: Make sure to disable the sampler before it is destroyed, in
        // case the profiler is running at the same time.
        sampler.Disable(lock);
      }
      break;
    }
  }
}

// END externally visible functions
////////////////////////////////////////////////////////////////////////

}  // namespace baseprofiler
}  // namespace mozilla