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// Copyright 2008, Google Inc.
// All rights reserved.
//
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions are
// met:
//
// * Redistributions of source code must retain the above copyright
// notice, this list of conditions and the following disclaimer.
// * Redistributions in binary form must reproduce the above
// copyright notice, this list of conditions and the following disclaimer
// in the documentation and/or other materials provided with the
// distribution.
// * Neither the name of Google Inc. nor the names of its
// contributors may be used to endorse or promote products derived from
// this software without specific prior written permission.
//
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
#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();
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_EVIL_CONSTRUCTORS(Lock);
};
// A helper class that acquires the given Lock while the AutoLock is in scope.
class AutoLock {
public:
AutoLock(Lock& lock) : lock_(lock) {
lock_.Acquire();
}
~AutoLock() {
lock_.Release();
}
private:
Lock& lock_;
DISALLOW_EVIL_CONSTRUCTORS(AutoLock);
};
// A helper macro to perform a single operation (expressed by expr)
// in a lock
#define LOCKED_EXPRESSION(lock, expr) \
do { \
AutoLock _auto_lock(lock); \
(expr); \
} while (0)
// 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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