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diff --git a/mozglue/baseprofiler/public/BaseProfilerDetail.h b/mozglue/baseprofiler/public/BaseProfilerDetail.h
new file mode 100644
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+++ b/mozglue/baseprofiler/public/BaseProfilerDetail.h
@@ -0,0 +1,285 @@
+/* -*- Mode: C++; tab-width: 2; 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/. */
+
+// Internal Base Profiler utilities.
+
+#ifndef BaseProfilerDetail_h
+#define BaseProfilerDetail_h
+
+#include "mozilla/Atomics.h"
+#include "mozilla/Attributes.h"
+#include "mozilla/Maybe.h"
+#include "mozilla/PlatformMutex.h"
+#include "mozilla/PlatformRWLock.h"
+#include "mozilla/BaseProfilerUtils.h"
+
+namespace mozilla {
+namespace baseprofiler {
+
+namespace detail {
+
+// Thin shell around mozglue PlatformMutex, for Base Profiler internal use.
+class MOZ_CAPABILITY("mutex") BaseProfilerMutex
+    : private ::mozilla::detail::MutexImpl {
+ public:
+  BaseProfilerMutex() : ::mozilla::detail::MutexImpl() {}
+  explicit BaseProfilerMutex(const char* aName)
+      : ::mozilla::detail::MutexImpl(), mName(aName) {}
+
+  BaseProfilerMutex(const BaseProfilerMutex&) = delete;
+  BaseProfilerMutex& operator=(const BaseProfilerMutex&) = delete;
+  BaseProfilerMutex(BaseProfilerMutex&&) = delete;
+  BaseProfilerMutex& operator=(BaseProfilerMutex&&) = delete;
+
+#ifdef DEBUG
+  ~BaseProfilerMutex() {
+    MOZ_ASSERT(!BaseProfilerThreadId::FromNumber(mOwningThreadId).IsSpecified(),
+               "BaseProfilerMutex should have been unlocked when destroyed");
+  }
+#endif  // DEBUG
+
+  [[nodiscard]] bool IsLockedOnCurrentThread() const {
+    return BaseProfilerThreadId::FromNumber(mOwningThreadId) ==
+           baseprofiler::profiler_current_thread_id();
+  }
+
+  void AssertCurrentThreadOwns() const MOZ_ASSERT_CAPABILITY(this) {
+    MOZ_ASSERT(IsLockedOnCurrentThread());
+  }
+
+  void Lock() MOZ_CAPABILITY_ACQUIRE() {
+    const BaseProfilerThreadId tid = baseprofiler::profiler_current_thread_id();
+    MOZ_ASSERT(tid.IsSpecified());
+    MOZ_ASSERT(!IsLockedOnCurrentThread(), "Recursive locking");
+    ::mozilla::detail::MutexImpl::lock();
+    MOZ_ASSERT(!BaseProfilerThreadId::FromNumber(mOwningThreadId).IsSpecified(),
+               "Not unlocked properly");
+    mOwningThreadId = tid.ToNumber();
+  }
+
+  [[nodiscard]] bool TryLock() MOZ_TRY_ACQUIRE(true) {
+    const BaseProfilerThreadId tid = baseprofiler::profiler_current_thread_id();
+    MOZ_ASSERT(tid.IsSpecified());
+    MOZ_ASSERT(!IsLockedOnCurrentThread(), "Recursive locking");
+    if (!::mozilla::detail::MutexImpl::tryLock()) {
+      // Failed to lock, nothing more to do.
+      return false;
+    }
+    MOZ_ASSERT(!BaseProfilerThreadId::FromNumber(mOwningThreadId).IsSpecified(),
+               "Not unlocked properly");
+    mOwningThreadId = tid.ToNumber();
+    return true;
+  }
+
+  void Unlock() MOZ_CAPABILITY_RELEASE() {
+    MOZ_ASSERT(IsLockedOnCurrentThread(), "Unlocking when not locked here");
+    // We're still holding the mutex here, so it's safe to just reset
+    // `mOwningThreadId`.
+    mOwningThreadId = BaseProfilerThreadId{}.ToNumber();
+    ::mozilla::detail::MutexImpl::unlock();
+  }
+
+  const char* GetName() const { return mName; }
+
+ private:
+  // Thread currently owning the lock, or 0.
+  // Atomic because it may be read at any time independent of the mutex.
+  // Relaxed because threads only need to know if they own it already, so:
+  // - If it's their id, only *they* wrote that value with a locked mutex.
+  // - If it's different from their thread id it doesn't matter what other
+  //   number it is (0 or another id) and that it can change again at any time.
+  Atomic<typename BaseProfilerThreadId::NumberType, MemoryOrdering::Relaxed>
+      mOwningThreadId;
+
+  const char* mName = nullptr;
+};
+
+// RAII class to lock a mutex.
+class MOZ_RAII BaseProfilerAutoLock {
+ public:
+  explicit BaseProfilerAutoLock(BaseProfilerMutex& aMutex) : mMutex(aMutex) {
+    mMutex.Lock();
+  }
+
+  BaseProfilerAutoLock(const BaseProfilerAutoLock&) = delete;
+  BaseProfilerAutoLock& operator=(const BaseProfilerAutoLock&) = delete;
+  BaseProfilerAutoLock(BaseProfilerAutoLock&&) = delete;
+  BaseProfilerAutoLock& operator=(BaseProfilerAutoLock&&) = delete;
+
+  ~BaseProfilerAutoLock() { mMutex.Unlock(); }
+
+ private:
+  BaseProfilerMutex& mMutex;
+};
+
+// Thin shell around mozglue PlatformMutex, for Base Profiler internal use.
+// Actual mutex may be disabled at construction time.
+class BaseProfilerMaybeMutex : private ::mozilla::detail::MutexImpl {
+ public:
+  explicit BaseProfilerMaybeMutex(bool aActivate) {
+    if (aActivate) {
+      mMaybeMutex.emplace();
+    }
+  }
+
+  BaseProfilerMaybeMutex(const BaseProfilerMaybeMutex&) = delete;
+  BaseProfilerMaybeMutex& operator=(const BaseProfilerMaybeMutex&) = delete;
+  BaseProfilerMaybeMutex(BaseProfilerMaybeMutex&&) = delete;
+  BaseProfilerMaybeMutex& operator=(BaseProfilerMaybeMutex&&) = delete;
+
+  ~BaseProfilerMaybeMutex() = default;
+
+  bool IsActivated() const { return mMaybeMutex.isSome(); }
+
+  [[nodiscard]] bool IsActivatedAndLockedOnCurrentThread() const {
+    if (!IsActivated()) {
+      // Not activated, so we can never be locked.
+      return false;
+    }
+    return mMaybeMutex->IsLockedOnCurrentThread();
+  }
+
+  void AssertCurrentThreadOwns() const {
+#ifdef DEBUG
+    if (IsActivated()) {
+      mMaybeMutex->AssertCurrentThreadOwns();
+    }
+#endif  // DEBUG
+  }
+
+  MOZ_PUSH_IGNORE_THREAD_SAFETY
+  void Lock() {
+    if (IsActivated()) {
+      mMaybeMutex->Lock();
+    }
+  }
+
+  void Unlock() {
+    if (IsActivated()) {
+      mMaybeMutex->Unlock();
+    }
+  }
+  MOZ_POP_THREAD_SAFETY
+
+ private:
+  Maybe<BaseProfilerMutex> mMaybeMutex;
+};
+
+// RAII class to lock a mutex.
+class MOZ_RAII BaseProfilerMaybeAutoLock {
+ public:
+  explicit BaseProfilerMaybeAutoLock(BaseProfilerMaybeMutex& aMaybeMutex)
+      : mMaybeMutex(aMaybeMutex) {
+    mMaybeMutex.Lock();
+  }
+
+  BaseProfilerMaybeAutoLock(const BaseProfilerMaybeAutoLock&) = delete;
+  BaseProfilerMaybeAutoLock& operator=(const BaseProfilerMaybeAutoLock&) =
+      delete;
+  BaseProfilerMaybeAutoLock(BaseProfilerMaybeAutoLock&&) = delete;
+  BaseProfilerMaybeAutoLock& operator=(BaseProfilerMaybeAutoLock&&) = delete;
+
+  ~BaseProfilerMaybeAutoLock() { mMaybeMutex.Unlock(); }
+
+ private:
+  BaseProfilerMaybeMutex& mMaybeMutex;
+};
+
+class BaseProfilerSharedMutex : public ::mozilla::detail::RWLockImpl {
+ public:
+#ifdef DEBUG
+  ~BaseProfilerSharedMutex() {
+    MOZ_ASSERT(!BaseProfilerThreadId::FromNumber(mOwningThreadId).IsSpecified(),
+               "BaseProfilerMutex should have been unlocked when destroyed");
+  }
+#endif  // DEBUG
+
+  [[nodiscard]] bool IsLockedExclusiveOnCurrentThread() const {
+    return BaseProfilerThreadId::FromNumber(mOwningThreadId) ==
+           baseprofiler::profiler_current_thread_id();
+  }
+
+  void LockExclusive() {
+    const BaseProfilerThreadId tid = baseprofiler::profiler_current_thread_id();
+    MOZ_ASSERT(tid.IsSpecified());
+    MOZ_ASSERT(!IsLockedExclusiveOnCurrentThread(), "Recursive locking");
+    ::mozilla::detail::RWLockImpl::writeLock();
+    MOZ_ASSERT(!BaseProfilerThreadId::FromNumber(mOwningThreadId).IsSpecified(),
+               "Not unlocked properly");
+    mOwningThreadId = tid.ToNumber();
+  }
+
+  void UnlockExclusive() {
+    MOZ_ASSERT(IsLockedExclusiveOnCurrentThread(),
+               "Unlocking when not locked here");
+    // We're still holding the mutex here, so it's safe to just reset
+    // `mOwningThreadId`.
+    mOwningThreadId = BaseProfilerThreadId{}.ToNumber();
+    writeUnlock();
+  }
+
+  void LockShared() { readLock(); }
+
+  void UnlockShared() { readUnlock(); }
+
+ private:
+  // Thread currently owning the exclusive lock, or 0.
+  // Atomic because it may be read at any time independent of the mutex.
+  // Relaxed because threads only need to know if they own it already, so:
+  // - If it's their id, only *they* wrote that value with a locked mutex.
+  // - If it's different from their thread id it doesn't matter what other
+  //   number it is (0 or another id) and that it can change again at any time.
+  Atomic<typename BaseProfilerThreadId::NumberType, MemoryOrdering::Relaxed>
+      mOwningThreadId;
+};
+
+// RAII class to lock a shared mutex exclusively.
+class MOZ_RAII BaseProfilerAutoLockExclusive {
+ public:
+  explicit BaseProfilerAutoLockExclusive(BaseProfilerSharedMutex& aSharedMutex)
+      : mSharedMutex(aSharedMutex) {
+    mSharedMutex.LockExclusive();
+  }
+
+  BaseProfilerAutoLockExclusive(const BaseProfilerAutoLockExclusive&) = delete;
+  BaseProfilerAutoLockExclusive& operator=(
+      const BaseProfilerAutoLockExclusive&) = delete;
+  BaseProfilerAutoLockExclusive(BaseProfilerAutoLockExclusive&&) = delete;
+  BaseProfilerAutoLockExclusive& operator=(BaseProfilerAutoLockExclusive&&) =
+      delete;
+
+  ~BaseProfilerAutoLockExclusive() { mSharedMutex.UnlockExclusive(); }
+
+ private:
+  BaseProfilerSharedMutex& mSharedMutex;
+};
+
+// RAII class to lock a shared mutex non-exclusively, other
+// BaseProfilerAutoLockShared's may happen in other threads.
+class MOZ_RAII BaseProfilerAutoLockShared {
+ public:
+  explicit BaseProfilerAutoLockShared(BaseProfilerSharedMutex& aSharedMutex)
+      : mSharedMutex(aSharedMutex) {
+    mSharedMutex.LockShared();
+  }
+
+  BaseProfilerAutoLockShared(const BaseProfilerAutoLockShared&) = delete;
+  BaseProfilerAutoLockShared& operator=(const BaseProfilerAutoLockShared&) =
+      delete;
+  BaseProfilerAutoLockShared(BaseProfilerAutoLockShared&&) = delete;
+  BaseProfilerAutoLockShared& operator=(BaseProfilerAutoLockShared&&) = delete;
+
+  ~BaseProfilerAutoLockShared() { mSharedMutex.UnlockShared(); }
+
+ private:
+  BaseProfilerSharedMutex& mSharedMutex;
+};
+
+}  // namespace detail
+}  // namespace baseprofiler
+}  // namespace mozilla
+
+#endif  // BaseProfilerDetail_h