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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_LOCK_H_
#define BASE_LOCK_H_
#include "base/basictypes.h"
#include "base/lock_impl.h"
#include "base/platform_thread.h"
#include "build/build_config.h"
// A convenient wrapper for an OS specific critical section.
class Lock {
public:
// 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 {}
// 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 base::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:
// Platform specific underlying lock implementation.
::base::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);
};
#endif // BASE_LOCK_H_
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