serge-sans-paille
ec94a9431e
While we're at it, make the copy-constructor deleted instead of private in DEBUG mode. This makes MOZ_RELEASE_CONSTINIT obsolete. Differential Revision: https://phabricator.services.mozilla.com/D290045
82 lines
2.4 KiB
C++
82 lines
2.4 KiB
C++
/* This Source Code Form is subject to the terms of the Mozilla Public
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* License, v. 2.0. If a copy of the MPL was not distributed with this
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* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
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#ifndef mozilla_StaticMutex_h
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#define mozilla_StaticMutex_h
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#include "mozilla/Atomics.h"
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#include "mozilla/Mutex.h"
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namespace mozilla {
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/**
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* StaticMutex is a Mutex that can (and in fact, must) be used as a
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* global/static variable.
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*
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* The main reason to use StaticMutex as opposed to
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* StaticAutoPtr<OffTheBooksMutex> is that we instantiate the StaticMutex in a
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* thread-safe manner the first time it's used.
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*
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* The same caveats that apply to StaticAutoPtr apply to StaticMutex. In
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* particular, do not use StaticMutex as a stack variable or a class instance
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* variable, because this class relies on the fact that global variablies are
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* initialized to 0 in order to initialize mMutex. It is only safe to use
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* StaticMutex as a global or static variable.
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*/
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class MOZ_ONLY_USED_TO_AVOID_STATIC_CONSTRUCTORS MOZ_CAPABILITY("mutex")
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StaticMutex {
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public:
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void Lock() MOZ_CAPABILITY_ACQUIRE() { Mutex()->Lock(); }
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[[nodiscard]] bool TryLock() MOZ_TRY_ACQUIRE(true) {
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return Mutex()->TryLock();
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}
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void Unlock() MOZ_CAPABILITY_RELEASE() { Mutex()->Unlock(); }
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void AssertCurrentThreadOwns() MOZ_ASSERT_CAPABILITY(this) {
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#ifdef DEBUG
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Mutex()->AssertCurrentThreadOwns();
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#endif
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}
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StaticMutex() = default;
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// Disallow copy constructor, but only in debug mode. We only define
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// a default constructor in debug mode (see above); if we declared
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// this constructor always, the compiler wouldn't generate a trivial
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// default constructor for us in non-debug mode.
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#ifdef DEBUG
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StaticMutex(StaticMutex& aOther) = delete;
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#endif
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private:
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OffTheBooksMutex* Mutex() {
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if (mMutex) {
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return mMutex;
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}
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OffTheBooksMutex* mutex = new OffTheBooksMutex("StaticMutex");
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if (!mMutex.compareExchange(nullptr, mutex)) {
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delete mutex;
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}
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return mMutex;
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}
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Atomic<OffTheBooksMutex*, SequentiallyConsistent> mMutex{nullptr};
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// Disallow these operators.
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StaticMutex& operator=(StaticMutex* aRhs);
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static void* operator new(size_t) noexcept(true);
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static void operator delete(void*);
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};
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typedef detail::BaseAutoLock<StaticMutex&> StaticMutexAutoLock;
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typedef detail::BaseAutoUnlock<StaticMutex&> StaticMutexAutoUnlock;
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} // namespace mozilla
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#endif
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