1 files changed, 263 insertions, 0 deletions
diff --git a/memory/build/Mutex.h b/memory/build/Mutex.h
new file mode 100644
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+++ b/memory/build/Mutex.h
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+/* -*- 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/. */
+
+#ifndef Mutex_h
+#define Mutex_h
+
+#if defined(XP_WIN)
+#  include <windows.h>
+#else
+#  include <pthread.h>
+#endif
+#if defined(XP_DARWIN)
+#  include <os/lock.h>
+#endif
+
+#include "mozilla/Assertions.h"
+#include "mozilla/Attributes.h"
+#include "mozilla/ThreadSafety.h"
+
+#if defined(XP_DARWIN)
+// For information about the following undocumented flags and functions see
+// https://github.com/apple/darwin-xnu/blob/main/bsd/sys/ulock.h and
+// https://github.com/apple/darwin-libplatform/blob/main/private/os/lock_private.h
+#  define OS_UNFAIR_LOCK_DATA_SYNCHRONIZATION (0x00010000)
+#  define OS_UNFAIR_LOCK_ADAPTIVE_SPIN (0x00040000)
+
+extern "C" {
+
+typedef uint32_t os_unfair_lock_options_t;
+OS_UNFAIR_LOCK_AVAILABILITY
+OS_EXPORT OS_NOTHROW OS_NONNULL_ALL void os_unfair_lock_lock_with_options(
+    os_unfair_lock_t lock, os_unfair_lock_options_t options);
+}
+#endif  // defined(XP_DARWIN)
+
+// Mutexes based on spinlocks.  We can't use normal pthread spinlocks in all
+// places, because they require malloc()ed memory, which causes bootstrapping
+// issues in some cases.  We also can't use constructors, because for statics,
+// they would fire after the first use of malloc, resetting the locks.
+struct MOZ_CAPABILITY("mutex") Mutex {
+#if defined(XP_WIN)
+  CRITICAL_SECTION mMutex;
+#elif defined(XP_DARWIN)
+  os_unfair_lock mMutex;
+#else
+  pthread_mutex_t mMutex;
+#endif
+
+  // Initializes a mutex. Returns whether initialization succeeded.
+  inline bool Init() {
+#if defined(XP_WIN)
+    if (!InitializeCriticalSectionAndSpinCount(&mMutex, 5000)) {
+      return false;
+    }
+#elif defined(XP_DARWIN)
+    mMutex = OS_UNFAIR_LOCK_INIT;
+#elif defined(XP_LINUX) && !defined(ANDROID)
+    pthread_mutexattr_t attr;
+    if (pthread_mutexattr_init(&attr) != 0) {
+      return false;
+    }
+    pthread_mutexattr_settype(&attr, PTHREAD_MUTEX_ADAPTIVE_NP);
+    if (pthread_mutex_init(&mMutex, &attr) != 0) {
+      pthread_mutexattr_destroy(&attr);
+      return false;
+    }
+    pthread_mutexattr_destroy(&attr);
+#else
+    if (pthread_mutex_init(&mMutex, nullptr) != 0) {
+      return false;
+    }
+#endif
+    return true;
+  }
+
+  inline void Lock() MOZ_CAPABILITY_ACQUIRE() {
+#if defined(XP_WIN)
+    EnterCriticalSection(&mMutex);
+#elif defined(XP_DARWIN)
+    // We rely on a non-public function to improve performance here.
+    // The OS_UNFAIR_LOCK_DATA_SYNCHRONIZATION flag informs the kernel that
+    // the calling thread is able to make progress even in absence of actions
+    // from other threads and the OS_UNFAIR_LOCK_ADAPTIVE_SPIN one causes the
+    // kernel to spin on a contested lock if the owning thread is running on
+    // the same physical core (presumably only on x86 CPUs given that ARM
+    // macs don't have cores capable of SMT).
+    os_unfair_lock_lock_with_options(
+        &mMutex,
+        OS_UNFAIR_LOCK_DATA_SYNCHRONIZATION | OS_UNFAIR_LOCK_ADAPTIVE_SPIN);
+#else
+    pthread_mutex_lock(&mMutex);
+#endif
+  }
+
+  [[nodiscard]] bool TryLock() MOZ_TRY_ACQUIRE(true);
+
+  inline void Unlock() MOZ_CAPABILITY_RELEASE() {
+#if defined(XP_WIN)
+    LeaveCriticalSection(&mMutex);
+#elif defined(XP_DARWIN)
+    os_unfair_lock_unlock(&mMutex);
+#else
+    pthread_mutex_unlock(&mMutex);
+#endif
+  }
+
+#if defined(XP_DARWIN)
+  static bool SpinInKernelSpace();
+  static const bool gSpinInKernelSpace;
+#endif  // XP_DARWIN
+};
+
+// Mutex that can be used for static initialization.
+// On Windows, CRITICAL_SECTION requires a function call to be initialized,
+// but for the initialization lock, a static initializer calling the
+// function would be called too late. We need no-function-call
+// initialization, which SRWLock provides.
+// Ideally, we'd use the same type of locks everywhere, but SRWLocks
+// everywhere incur a performance penalty. See bug 1418389.
+#if defined(XP_WIN)
+struct MOZ_CAPABILITY("mutex") StaticMutex {
+  SRWLOCK mMutex;
+
+  inline void Lock() MOZ_CAPABILITY_ACQUIRE() {
+    AcquireSRWLockExclusive(&mMutex);
+  }
+
+  inline void Unlock() MOZ_CAPABILITY_RELEASE() {
+    ReleaseSRWLockExclusive(&mMutex);
+  }
+};
+
+// Normally, we'd use a constexpr constructor, but MSVC likes to create
+// static initializers anyways.
+#  define STATIC_MUTEX_INIT SRWLOCK_INIT
+
+#else
+typedef Mutex StaticMutex;
+
+#  if defined(XP_DARWIN)
+#    define STATIC_MUTEX_INIT OS_UNFAIR_LOCK_INIT
+#  elif defined(XP_LINUX) && !defined(ANDROID)
+#    define STATIC_MUTEX_INIT PTHREAD_ADAPTIVE_MUTEX_INITIALIZER_NP
+#  else
+#    define STATIC_MUTEX_INIT PTHREAD_MUTEX_INITIALIZER
+#  endif
+
+#endif
+
+#ifdef XP_WIN
+typedef DWORD ThreadId;
+inline ThreadId GetThreadId() { return GetCurrentThreadId(); }
+#else
+typedef pthread_t ThreadId;
+inline ThreadId GetThreadId() { return pthread_self(); }
+#endif
+
+class MOZ_CAPABILITY("mutex") MaybeMutex : public Mutex {
+ public:
+  enum DoLock {
+    MUST_LOCK,
+    AVOID_LOCK_UNSAFE,
+  };
+
+  bool Init(DoLock aDoLock) {
+    mDoLock = aDoLock;
+#ifdef MOZ_DEBUG
+    mThreadId = GetThreadId();
+#endif
+    return Mutex::Init();
+  }
+
+#ifndef XP_WIN
+  // Re initialise after fork(), assumes that mDoLock is already initialised.
+  void Reinit(pthread_t aForkingThread) {
+    if (mDoLock == MUST_LOCK) {
+      Mutex::Init();
+      return;
+    }
+#  ifdef MOZ_DEBUG
+    // If this is an eluded lock we can only safely re-initialise it if the
+    // thread that called fork is the one that owns the lock.
+    if (pthread_equal(mThreadId, aForkingThread)) {
+      mThreadId = GetThreadId();
+      Mutex::Init();
+    } else {
+      // We can't guantee that whatever resource this lock protects (probably a
+      // jemalloc arena) is in a consistent state.
+      mDeniedAfterFork = true;
+    }
+#  endif
+  }
+#endif
+
+  inline void Lock() MOZ_CAPABILITY_ACQUIRE() {
+    if (ShouldLock()) {
+      Mutex::Lock();
+    }
+  }
+
+  inline void Unlock() MOZ_CAPABILITY_RELEASE() {
+    if (ShouldLock()) {
+      Mutex::Unlock();
+    }
+  }
+
+  // Return true if we can use this resource from this thread, either because
+  // we'll use the lock or because this is the only thread that will access the
+  // protected resource.
+#ifdef MOZ_DEBUG
+  bool SafeOnThisThread() const {
+    return mDoLock == MUST_LOCK || GetThreadId() == mThreadId;
+  }
+#endif
+
+  bool LockIsEnabled() const { return mDoLock == MUST_LOCK; }
+
+ private:
+  bool ShouldLock() {
+#ifndef XP_WIN
+    MOZ_ASSERT(!mDeniedAfterFork);
+#endif
+
+    if (mDoLock == MUST_LOCK) {
+      return true;
+    }
+
+    MOZ_ASSERT(GetThreadId() == mThreadId);
+    return false;
+  }
+
+  DoLock mDoLock;
+#ifdef MOZ_DEBUG
+  ThreadId mThreadId;
+#  ifndef XP_WIN
+  bool mDeniedAfterFork = false;
+#  endif
+#endif
+};
+
+template <typename T>
+struct MOZ_SCOPED_CAPABILITY MOZ_RAII AutoLock {
+  explicit AutoLock(T& aMutex) MOZ_CAPABILITY_ACQUIRE(aMutex) : mMutex(aMutex) {
+    mMutex.Lock();
+  }
+
+  ~AutoLock() MOZ_CAPABILITY_RELEASE() { mMutex.Unlock(); }
+
+  AutoLock(const AutoLock&) = delete;
+  AutoLock(AutoLock&&) = delete;
+
+ private:
+  T& mMutex;
+};
+
+using MutexAutoLock = AutoLock<Mutex>;
+
+using MaybeMutexAutoLock = AutoLock<MaybeMutex>;
+
+#endif