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// Copyright (c) 2006-2008 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/lock_impl.h"
// A convenient wrapper for a critical section.
//
// NOTE: A thread may acquire the same lock multiple times, but it must call
// Release for each call to Acquire in order to finally release the lock.
//
// Complication: UnitTest for DeathTests catch DCHECK exceptions, so we need
// to write code assuming DCHECK will throw. This means we need to save any
// assertable value in a local until we can safely throw.
class Lock {
public:
Lock();
~Lock();
void Acquire();
void Release();
// If the lock is not held, take it and return true. If the lock is already
// held by something else, immediately return false.
bool Try();
// Return the underlying lock implementation.
// TODO(awalker): refactor lock and condition variables so that this is
// unnecessary.
LockImpl* lock_impl() { return &lock_; }
private:
LockImpl lock_; // User-supplied underlying lock implementation.
// All private data is implicitly protected by spin_lock_.
// Be VERY careful to only access under that lock.
int32 recursion_count_shadow_;
// Allow access to GetCurrentThreadRecursionCount()
friend class AutoUnlock;
int32 GetCurrentThreadRecursionCount();
#ifndef NDEBUG
// Even in Debug mode, the expensive tallies won't be calculated by default.
bool recursion_used_;
int32 acquisition_count_;
int32 contention_count_;
#endif // NDEBUG
DISALLOW_COPY_AND_ASSIGN(Lock);
};
// A helper class that acquires the given Lock while the AutoLock is in scope.
class AutoLock {
public:
explicit AutoLock(Lock& lock) : lock_(lock) {
lock_.Acquire();
}
~AutoLock() {
lock_.Release();
}
private:
Lock& lock_;
DISALLOW_COPY_AND_ASSIGN(AutoLock);
};
// AutoUnlock is a helper class for ConditionVariable instances
// that is analogous to AutoLock. It provides for nested Releases
// of a lock for the Wait functionality of a ConditionVariable class.
// The destructor automatically does the corresponding Acquire
// calls (to return to the initial nested lock state).
// Instances of AutoUnlock can ***ONLY*** validly be constructed if the
// caller currently holds the lock provided as the constructor's argument.
// If that ***REQUIREMENT*** is violated in debug mode, a DCHECK will
// be generated in the Lock class. In production (non-debug),
// the results are undefined (and probably bad) if the caller
// is not already holding the indicated lock.
class ConditionVariable;
class AutoUnlock {
private: // Everything is private, so only our friend can use us.
friend class ConditionVariable; // The only user of this class.
explicit AutoUnlock(Lock& lock);
~AutoUnlock();
Lock* lock_;
int release_count_;
};
#endif // BASE_LOCK_H_
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