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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 threading_Mutex_h
#define threading_Mutex_h
#include "mozilla/Assertions.h"
#include "mozilla/Maybe.h"
#include "mozilla/PlatformMutex.h"
#include "mozilla/ThreadLocal.h"
#include "mozilla/Vector.h"
#include <utility>
#include "threading/ThreadId.h"
namespace js {
// A MutexId secifies the name and mutex order for a mutex.
//
// The mutex order defines the allowed order of mutex acqusition on a single
// thread. Mutexes must be acquired in strictly increasing order. Mutexes with
// the same order may not be held at the same time by that thread.
struct MutexId {
const char* name;
uint32_t order;
};
// The Mutex class below wraps mozilla::detail::MutexImpl, but we don't want to
// use public inheritance, and private inheritance is problematic because
// Mutex's friends can access the private parent class as if it was public
// inheritance. So use a data member, but for Mutex to access the data member
// we must override it and make Mutex a friend.
class MutexImpl : public mozilla::detail::MutexImpl {
protected:
MutexImpl() : mozilla::detail::MutexImpl() {}
friend class Mutex;
};
// In debug builds, js::Mutex is a wrapper over MutexImpl that checks correct
// locking order is observed.
//
// The class maintains a per-thread stack of currently-held mutexes to enable it
// to check this.
class Mutex {
private:
MutexImpl impl_;
#ifdef DEBUG
const MutexId id_;
Mutex* prev_ = nullptr;
ThreadId owningThread_;
static MOZ_THREAD_LOCAL(Mutex*) HeldMutexStack;
#endif
public:
#ifdef DEBUG
static bool Init();
explicit Mutex(const MutexId& id) : id_(id) { MOZ_ASSERT(id_.order != 0); }
void lock();
bool tryLock();
void unlock();
void assertOwnedByCurrentThread() const;
#else
static bool Init() { return true; }
explicit Mutex(const MutexId& id) {}
void lock() { impl_.lock(); }
bool tryLock() { return impl_.tryLock(); }
void unlock() { impl_.unlock(); }
void assertOwnedByCurrentThread() const {};
#endif
private:
#ifdef DEBUG
void preLockChecks() const;
void postLockChecks();
void preUnlockChecks();
#endif
friend class ConditionVariable;
};
} // namespace js
#endif // threading_Mutex_h
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