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authorDaniel Baumann <daniel.baumann@progress-linux.org>2024-04-19 01:47:29 +0000
committerDaniel Baumann <daniel.baumann@progress-linux.org>2024-04-19 01:47:29 +0000
commit0ebf5bdf043a27fd3dfb7f92e0cb63d88954c44d (patch)
treea31f07c9bcca9d56ce61e9a1ffd30ef350d513aa /xpcom/threads/Mutex.h
parentInitial commit. (diff)
downloadfirefox-esr-upstream/115.8.0esr.tar.xz
firefox-esr-upstream/115.8.0esr.zip
Adding upstream version 115.8.0esr.upstream/115.8.0esr
Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
Diffstat (limited to 'xpcom/threads/Mutex.h')
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diff --git a/xpcom/threads/Mutex.h b/xpcom/threads/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 mozilla_Mutex_h
+#define mozilla_Mutex_h
+
+#include "mozilla/BlockingResourceBase.h"
+#include "mozilla/ThreadSafety.h"
+#include "mozilla/PlatformMutex.h"
+#include "nsISupports.h"
+
+//
+// Provides:
+//
+// - Mutex, a non-recursive mutex
+// - MutexAutoLock, an RAII class for ensuring that Mutexes are properly
+// locked and unlocked
+// - MutexAutoUnlock, complementary sibling to MutexAutoLock
+//
+// - OffTheBooksMutex, a non-recursive mutex that doesn't do leak checking
+// - OffTheBooksMutexAuto{Lock,Unlock} - Like MutexAuto{Lock,Unlock}, but for
+// an OffTheBooksMutex.
+//
+// Using MutexAutoLock/MutexAutoUnlock etc. is MUCH preferred to making bare
+// calls to Lock and Unlock.
+//
+namespace mozilla {
+
+/**
+ * OffTheBooksMutex is identical to Mutex, except that OffTheBooksMutex doesn't
+ * include leak checking. Sometimes you want to intentionally "leak" a mutex
+ * until shutdown; in these cases, OffTheBooksMutex is for you.
+ */
+class MOZ_CAPABILITY("mutex") OffTheBooksMutex : public detail::MutexImpl,
+ BlockingResourceBase {
+ public:
+ /**
+ * @param aName A name which can reference this lock
+ * @returns If failure, nullptr
+ * If success, a valid Mutex* which must be destroyed
+ * by Mutex::DestroyMutex()
+ **/
+ explicit OffTheBooksMutex(const char* aName)
+ : BlockingResourceBase(aName, eMutex)
+#ifdef DEBUG
+ ,
+ mOwningThread(nullptr)
+#endif
+ {
+ }
+
+ ~OffTheBooksMutex() {
+#ifdef DEBUG
+ MOZ_ASSERT(!mOwningThread, "destroying a still-owned lock!");
+#endif
+ }
+
+#ifndef DEBUG
+ /**
+ * Lock this mutex.
+ **/
+ void Lock() MOZ_CAPABILITY_ACQUIRE() { this->lock(); }
+
+ /**
+ * Try to lock this mutex, returning true if we were successful.
+ **/
+ [[nodiscard]] bool TryLock() MOZ_TRY_ACQUIRE(true) { return this->tryLock(); }
+
+ /**
+ * Unlock this mutex.
+ **/
+ void Unlock() MOZ_CAPABILITY_RELEASE() { this->unlock(); }
+
+ /**
+ * Assert that the current thread owns this mutex in debug builds.
+ *
+ * Does nothing in non-debug builds.
+ **/
+ void AssertCurrentThreadOwns() const MOZ_ASSERT_CAPABILITY(this) {}
+
+ /**
+ * Assert that the current thread does not own this mutex.
+ *
+ * Note that this function is not implemented for debug builds *and*
+ * non-debug builds due to difficulties in dealing with memory ordering.
+ *
+ * It is therefore mostly useful as documentation.
+ **/
+ void AssertNotCurrentThreadOwns() const MOZ_ASSERT_CAPABILITY(!this) {}
+
+#else
+ void Lock() MOZ_CAPABILITY_ACQUIRE();
+
+ [[nodiscard]] bool TryLock() MOZ_TRY_ACQUIRE(true);
+ void Unlock() MOZ_CAPABILITY_RELEASE();
+
+ void AssertCurrentThreadOwns() const MOZ_ASSERT_CAPABILITY(this);
+ void AssertNotCurrentThreadOwns() const MOZ_ASSERT_CAPABILITY(!this) {
+ // FIXME bug 476536
+ }
+#endif // ifndef DEBUG
+
+ private:
+ OffTheBooksMutex() = delete;
+ OffTheBooksMutex(const OffTheBooksMutex&) = delete;
+ OffTheBooksMutex& operator=(const OffTheBooksMutex&) = delete;
+
+ friend class OffTheBooksCondVar;
+
+#ifdef DEBUG
+ PRThread* mOwningThread;
+#endif
+};
+
+/**
+ * Mutex
+ * When possible, use MutexAutoLock/MutexAutoUnlock to lock/unlock this
+ * mutex within a scope, instead of calling Lock/Unlock directly.
+ */
+class Mutex : public OffTheBooksMutex {
+ public:
+ explicit Mutex(const char* aName) : OffTheBooksMutex(aName) {
+ MOZ_COUNT_CTOR(Mutex);
+ }
+
+ MOZ_COUNTED_DTOR(Mutex)
+
+ private:
+ Mutex() = delete;
+ Mutex(const Mutex&) = delete;
+ Mutex& operator=(const Mutex&) = delete;
+};
+
+/**
+ * MutexSingleWriter
+ *
+ * Mutex where a single writer exists, so that reads from the same thread
+ * will not generate data races or consistency issues.
+ *
+ * When possible, use MutexAutoLock/MutexAutoUnlock to lock/unlock this
+ * mutex within a scope, instead of calling Lock/Unlock directly.
+ *
+ * This requires an object implementing Mutex's SingleWriterLockOwner, so
+ * we can do correct-thread checks.
+ */
+// Subclass this in the object owning the mutex
+class SingleWriterLockOwner {
+ public:
+ SingleWriterLockOwner() = default;
+ ~SingleWriterLockOwner() = default;
+
+ virtual bool OnWritingThread() const = 0;
+};
+
+class MutexSingleWriter : public OffTheBooksMutex {
+ public:
+ // aOwner should be the object that contains the mutex, typically. We
+ // will use that object (which must have a lifetime the same or greater
+ // than this object) to verify that we're running on the correct thread,
+ // typically only in DEBUG builds
+ explicit MutexSingleWriter(const char* aName, SingleWriterLockOwner* aOwner)
+ : OffTheBooksMutex(aName)
+#ifdef DEBUG
+ ,
+ mOwner(aOwner)
+#endif
+ {
+ MOZ_COUNT_CTOR(MutexSingleWriter);
+ MOZ_ASSERT(mOwner);
+ }
+
+ MOZ_COUNTED_DTOR(MutexSingleWriter)
+
+ /**
+ * Statically assert that we're on the only thread that modifies data
+ * guarded by this Mutex. This allows static checking for the pattern of
+ * having a single thread modify a set of data, and read it (under lock)
+ * on other threads, and reads on the thread that modifies it doesn't
+ * require a lock. This doesn't solve the issue of some data under the
+ * Mutex following this pattern, and other data under the mutex being
+ * written from multiple threads.
+ *
+ * We could set the writing thread and dynamically check it in debug
+ * builds, but this doesn't. We could also use thread-safety/capability
+ * system to provide direct thread assertions.
+ **/
+ void AssertOnWritingThread() const MOZ_ASSERT_CAPABILITY(this) {
+ MOZ_ASSERT(mOwner->OnWritingThread());
+ }
+ void AssertOnWritingThreadOrHeld() const MOZ_ASSERT_CAPABILITY(this) {
+#ifdef DEBUG
+ if (!mOwner->OnWritingThread()) {
+ AssertCurrentThreadOwns();
+ }
+#endif
+ }
+
+ private:
+#ifdef DEBUG
+ SingleWriterLockOwner* mOwner MOZ_UNSAFE_REF(
+ "This is normally the object that contains the MonitorSingleWriter, so "
+ "we don't want to hold a reference to ourselves");
+#endif
+
+ MutexSingleWriter() = delete;
+ MutexSingleWriter(const MutexSingleWriter&) = delete;
+ MutexSingleWriter& operator=(const MutexSingleWriter&) = delete;
+};
+
+namespace detail {
+template <typename T>
+class MOZ_RAII BaseAutoUnlock;
+
+/**
+ * MutexAutoLock
+ * Acquires the Mutex when it enters scope, and releases it when it leaves
+ * scope.
+ *
+ * MUCH PREFERRED to bare calls to Mutex.Lock and Unlock.
+ */
+template <typename T>
+class MOZ_RAII MOZ_SCOPED_CAPABILITY BaseAutoLock {
+ public:
+ /**
+ * Constructor
+ * The constructor aquires the given lock. The destructor
+ * releases the lock.
+ *
+ * @param aLock A valid mozilla::Mutex* returned by
+ * mozilla::Mutex::NewMutex.
+ **/
+ explicit BaseAutoLock(T aLock) MOZ_CAPABILITY_ACQUIRE(aLock) : mLock(aLock) {
+ mLock.Lock();
+ }
+
+ ~BaseAutoLock(void) MOZ_CAPABILITY_RELEASE() { mLock.Unlock(); }
+
+ // Assert that aLock is the mutex passed to the constructor and that the
+ // current thread owns the mutex. In coding patterns such as:
+ //
+ // void LockedMethod(const BaseAutoLock<T>& aProofOfLock)
+ // {
+ // aProofOfLock.AssertOwns(mMutex);
+ // ...
+ // }
+ //
+ // Without this assertion, it could be that mMutex is not actually
+ // locked. It's possible to have code like:
+ //
+ // BaseAutoLock lock(someMutex);
+ // ...
+ // BaseAutoUnlock unlock(someMutex);
+ // ...
+ // LockedMethod(lock);
+ //
+ // and in such a case, simply asserting that the mutex pointers match is not
+ // sufficient; mutex ownership must be asserted as well.
+ //
+ // Note that if you are going to use the coding pattern presented above, you
+ // should use this method in preference to using AssertCurrentThreadOwns on
+ // the mutex you expected to be held, since this method provides stronger
+ // guarantees.
+ void AssertOwns(const T& aMutex) const MOZ_ASSERT_CAPABILITY(aMutex) {
+ MOZ_ASSERT(&aMutex == &mLock);
+ mLock.AssertCurrentThreadOwns();
+ }
+
+ private:
+ BaseAutoLock() = delete;
+ BaseAutoLock(BaseAutoLock&) = delete;
+ BaseAutoLock& operator=(BaseAutoLock&) = delete;
+ static void* operator new(size_t) noexcept(true);
+
+ friend class BaseAutoUnlock<T>;
+
+ T mLock;
+};
+
+template <typename MutexType>
+BaseAutoLock(MutexType&) -> BaseAutoLock<MutexType&>;
+} // namespace detail
+
+typedef detail::BaseAutoLock<Mutex&> MutexAutoLock;
+typedef detail::BaseAutoLock<MutexSingleWriter&> MutexSingleWriterAutoLock;
+typedef detail::BaseAutoLock<OffTheBooksMutex&> OffTheBooksMutexAutoLock;
+
+// Use if we've done AssertOnWritingThread(), and then later need to take the
+// lock to write to a protected member. Instead of
+// MutexSingleWriterAutoLock lock(mutex)
+// use
+// MutexSingleWriterAutoLockOnThread(lock, mutex)
+#define MutexSingleWriterAutoLockOnThread(lock, mutex) \
+ MOZ_PUSH_IGNORE_THREAD_SAFETY \
+ MutexSingleWriterAutoLock lock(mutex); \
+ MOZ_POP_THREAD_SAFETY
+
+namespace detail {
+/**
+ * ReleasableMutexAutoLock
+ * Acquires the Mutex when it enters scope, and releases it when it leaves
+ * scope. Allows calling Unlock (and Lock) as an alternative to
+ * MutexAutoUnlock; this can avoid an extra lock/unlock pair.
+ *
+ */
+template <typename T>
+class MOZ_RAII MOZ_SCOPED_CAPABILITY ReleasableBaseAutoLock {
+ public:
+ /**
+ * Constructor
+ * The constructor aquires the given lock. The destructor
+ * releases the lock.
+ *
+ * @param aLock A valid mozilla::Mutex& returned by
+ * mozilla::Mutex::NewMutex.
+ **/
+ explicit ReleasableBaseAutoLock(T aLock) MOZ_CAPABILITY_ACQUIRE(aLock)
+ : mLock(aLock) {
+ mLock.Lock();
+ mLocked = true;
+ }
+
+ ~ReleasableBaseAutoLock(void) MOZ_CAPABILITY_RELEASE() {
+ if (mLocked) {
+ Unlock();
+ }
+ }
+
+ void AssertOwns(const T& aMutex) const MOZ_ASSERT_CAPABILITY(aMutex) {
+ MOZ_ASSERT(&aMutex == &mLock);
+ mLock.AssertCurrentThreadOwns();
+ }
+
+ // Allow dropping the lock prematurely; for example to support something like:
+ // clang-format off
+ // MutexAutoLock lock(mMutex);
+ // ...
+ // if (foo) {
+ // lock.Unlock();
+ // MethodThatCantBeCalledWithLock()
+ // return;
+ // }
+ // clang-format on
+ void Unlock() MOZ_CAPABILITY_RELEASE() {
+ MOZ_ASSERT(mLocked);
+ mLock.Unlock();
+ mLocked = false;
+ }
+ void Lock() MOZ_CAPABILITY_ACQUIRE() {
+ MOZ_ASSERT(!mLocked);
+ mLock.Lock();
+ mLocked = true;
+ }
+
+ private:
+ ReleasableBaseAutoLock() = delete;
+ ReleasableBaseAutoLock(ReleasableBaseAutoLock&) = delete;
+ ReleasableBaseAutoLock& operator=(ReleasableBaseAutoLock&) = delete;
+ static void* operator new(size_t) noexcept(true);
+
+ bool mLocked;
+ T mLock;
+};
+
+template <typename MutexType>
+ReleasableBaseAutoLock(MutexType&) -> ReleasableBaseAutoLock<MutexType&>;
+} // namespace detail
+
+typedef detail::ReleasableBaseAutoLock<Mutex&> ReleasableMutexAutoLock;
+
+namespace detail {
+/**
+ * BaseAutoUnlock
+ * Releases the Mutex when it enters scope, and re-acquires it when it leaves
+ * scope.
+ *
+ * MUCH PREFERRED to bare calls to Mutex.Unlock and Lock.
+ */
+template <typename T>
+class MOZ_RAII MOZ_SCOPED_CAPABILITY BaseAutoUnlock {
+ public:
+ explicit BaseAutoUnlock(T aLock) MOZ_SCOPED_UNLOCK_RELEASE(aLock)
+ : mLock(aLock) {
+ mLock.Unlock();
+ }
+
+ explicit BaseAutoUnlock(BaseAutoLock<T>& aAutoLock)
+ /* MOZ_CAPABILITY_RELEASE(aAutoLock.mLock) */
+ : mLock(aAutoLock.mLock) {
+ NS_ASSERTION(mLock, "null lock");
+ mLock->Unlock();
+ }
+
+ ~BaseAutoUnlock() MOZ_SCOPED_UNLOCK_REACQUIRE() { mLock.Lock(); }
+
+ private:
+ BaseAutoUnlock() = delete;
+ BaseAutoUnlock(BaseAutoUnlock&) = delete;
+ BaseAutoUnlock& operator=(BaseAutoUnlock&) = delete;
+ static void* operator new(size_t) noexcept(true);
+
+ T mLock;
+};
+
+template <typename MutexType>
+BaseAutoUnlock(MutexType&) -> BaseAutoUnlock<MutexType&>;
+} // namespace detail
+
+typedef detail::BaseAutoUnlock<Mutex&> MutexAutoUnlock;
+typedef detail::BaseAutoUnlock<MutexSingleWriter&> MutexSingleWriterAutoUnlock;
+typedef detail::BaseAutoUnlock<OffTheBooksMutex&> OffTheBooksMutexAutoUnlock;
+
+namespace detail {
+/**
+ * BaseAutoTryLock
+ * Tries to acquire the Mutex when it enters scope, and releases it when it
+ * leaves scope.
+ *
+ * MUCH PREFERRED to bare calls to Mutex.TryLock and Unlock.
+ */
+template <typename T>
+class MOZ_RAII MOZ_SCOPED_CAPABILITY BaseAutoTryLock {
+ public:
+ explicit BaseAutoTryLock(T& aLock) MOZ_CAPABILITY_ACQUIRE(aLock)
+ : mLock(aLock.TryLock() ? &aLock : nullptr) {}
+
+ ~BaseAutoTryLock() MOZ_CAPABILITY_RELEASE() {
+ if (mLock) {
+ mLock->Unlock();
+ mLock = nullptr;
+ }
+ }
+
+ explicit operator bool() const { return mLock; }
+
+ private:
+ BaseAutoTryLock(BaseAutoTryLock&) = delete;
+ BaseAutoTryLock& operator=(BaseAutoTryLock&) = delete;
+ static void* operator new(size_t) noexcept(true);
+
+ T* mLock;
+};
+} // namespace detail
+
+typedef detail::BaseAutoTryLock<Mutex> MutexAutoTryLock;
+typedef detail::BaseAutoTryLock<OffTheBooksMutex> OffTheBooksMutexAutoTryLock;
+
+} // namespace mozilla
+
+#endif // ifndef mozilla_Mutex_h
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