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// Copyright (c) 2011 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#ifndef BASE_SYNCHRONIZATION_LOCK_H_
#define BASE_SYNCHRONIZATION_LOCK_H_
#include "base/base_export.h"
#include "base/logging.h"
#include "base/macros.h"
#include "base/synchronization/lock_impl.h"
#include "base/threading/platform_thread.h"
#include "build/build_config.h"
namespace base {
// A convenient wrapper for an OS specific critical section. The only real
// intelligence in this class is in debug mode for the support for the
// AssertAcquired() method.
class BASE_EXPORT Lock {
public:
#if !DCHECK_IS_ON()
// Optimized wrapper implementation
Lock() : lock_() {}
~Lock() {}
void Acquire() { lock_.Lock(); }
void Release() { lock_.Unlock(); }
// If the lock is not held, take it and return true. If the lock is already
// held by another thread, immediately return false. This must not be called
// by a thread already holding the lock (what happens is undefined and an
// assertion may fail).
bool Try() { return lock_.Try(); }
// Null implementation if not debug.
void AssertAcquired() const {}
#else
Lock();
~Lock();
// NOTE: We do not permit recursive locks and will commonly fire a DCHECK() if
// a thread attempts to acquire the lock a second time (while already holding
// it).
void Acquire() {
lock_.Lock();
CheckUnheldAndMark();
}
void Release() {
CheckHeldAndUnmark();
lock_.Unlock();
}
bool Try() {
bool rv = lock_.Try();
if (rv) {
CheckUnheldAndMark();
}
return rv;
}
void AssertAcquired() const;
#endif // DCHECK_IS_ON()
// Whether Lock mitigates priority inversion when used from different thread
// priorities.
static bool HandlesMultipleThreadPriorities() {
#if defined(OS_POSIX)
// POSIX mitigates priority inversion by setting the priority of a thread
// holding a Lock to the maximum priority of any other thread waiting on it.
return internal::LockImpl::PriorityInheritanceAvailable();
#elif defined(OS_WIN)
// Windows mitigates priority inversion by randomly boosting the priority of
// ready threads.
// https://msdn.microsoft.com/library/windows/desktop/ms684831.aspx
return true;
#else
#error Unsupported platform
#endif
}
#if defined(OS_POSIX) || defined(OS_WIN)
// Both Windows and POSIX implementations of ConditionVariable need to be
// able to see our lock and tweak our debugging counters, as they release and
// acquire locks inside of their condition variable APIs.
friend class ConditionVariable;
#endif
private:
#if DCHECK_IS_ON()
// Members and routines taking care of locks assertions.
// Note that this checks for recursive locks and allows them
// if the variable is set. This is allowed by the underlying implementation
// on windows but not on Posix, so we're doing unneeded checks on Posix.
// It's worth it to share the code.
void CheckHeldAndUnmark();
void CheckUnheldAndMark();
// All private data is implicitly protected by lock_.
// Be VERY careful to only access members under that lock.
base::PlatformThreadRef owning_thread_ref_;
#endif // DCHECK_IS_ON()
// Platform specific underlying lock implementation.
internal::LockImpl lock_;
DISALLOW_COPY_AND_ASSIGN(Lock);
};
// A helper class that acquires the given Lock while the AutoLock is in scope.
class AutoLock {
public:
struct AlreadyAcquired {};
explicit AutoLock(Lock& lock) : lock_(lock) {
lock_.Acquire();
}
AutoLock(Lock& lock, const AlreadyAcquired&) : lock_(lock) {
lock_.AssertAcquired();
}
~AutoLock() {
lock_.AssertAcquired();
lock_.Release();
}
private:
Lock& lock_;
DISALLOW_COPY_AND_ASSIGN(AutoLock);
};
// AutoUnlock is a helper that will Release() the |lock| argument in the
// constructor, and re-Acquire() it in the destructor.
class AutoUnlock {
public:
explicit AutoUnlock(Lock& lock) : lock_(lock) {
// We require our caller to have the lock.
lock_.AssertAcquired();
lock_.Release();
}
~AutoUnlock() {
lock_.Acquire();
}
private:
Lock& lock_;
DISALLOW_COPY_AND_ASSIGN(AutoUnlock);
};
} // namespace base
#endif // BASE_SYNCHRONIZATION_LOCK_H_
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