/usr/include/zthread/FairReadWriteLock.h is in libzthread-dev 2.3.2-8.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
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* Copyright (c) 2005, Eric Crahen
*
* Permission is hereby granted, free of charge, to any person obtaining a copy
* of this software and associated documentation files (the "Software"), to deal
* in the Software without restriction, including without limitation the rights
* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
* copies of the Software, and to permit persons to whom the Software is furnished
* to do so, subject to the following conditions:
*
* The above copyright notice and this permission notice shall be included in all
* copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
* WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
* CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
*
*/
#ifndef __ZTFAIRREADWRITELOCK_H__
#define __ZTFAIRREADWRITELOCK_H__
#include "zthread/ReadWriteLock.h"
#include "zthread/Condition.h"
#include "zthread/Guard.h"
#include "zthread/Mutex.h"
namespace ZThread {
/**
* @class FairReadWriteLock
*
* @author Eric Crahen <http://www.code-foo.com>
* @date <2003-07-16T10:26:25-0400>
* @version 2.2.7
*
* A FairReadWriteLock maintains a balance between the order read-only access
* and read-write access is allowed. Threads contending for the pair of Lockable
* objects this ReadWriteLock provides will gain access to the locks in FIFO order.
*
* @see ReadWriteLock
*/
class FairReadWriteLock : public ReadWriteLock {
Mutex _lock;
Condition _cond;
volatile int _readers;
//! @class ReadLock
class ReadLock : public Lockable {
FairReadWriteLock& _rwlock;
public:
ReadLock(FairReadWriteLock& rwlock) : _rwlock(rwlock) {}
virtual ~ReadLock() {}
virtual void acquire() {
Guard<Mutex> g(_rwlock._lock);
++_rwlock._readers;
}
virtual bool tryAcquire(unsigned long timeout) {
if(!_rwlock._lock.tryAcquire(timeout))
return false;
++_rwlock._readers;
_rwlock._lock.release();
return true;
}
virtual void release() {
Guard<Mutex> g(_rwlock._lock);
--_rwlock._readers;
if(_rwlock._readers == 0)
_rwlock._cond.signal();
}
};
//! @class WriteLock
class WriteLock : public Lockable {
FairReadWriteLock& _rwlock;
public:
WriteLock(FairReadWriteLock& rwlock) : _rwlock(rwlock) {}
virtual ~WriteLock() {}
virtual void acquire() {
_rwlock._lock.acquire();
try {
while(_rwlock._readers > 0)
_rwlock._cond.wait();
} catch(...) {
_rwlock._lock.release();
throw;
}
}
virtual bool tryAcquire(unsigned long timeout) {
if(!_rwlock._lock.tryAcquire(timeout))
return false;
try {
while(_rwlock._readers > 0)
_rwlock._cond.wait(timeout);
} catch(...) {
_rwlock._lock.release();
throw;
}
return true;
}
virtual void release() {
_rwlock._lock.release();
}
};
friend class ReadLock;
friend class WriteLock;
ReadLock _rlock;
WriteLock _wlock;
public:
/**
* Create a BiasedReadWriteLock
*
* @exception Initialization_Exception thrown if resources could not be
* allocated for this object.
*/
FairReadWriteLock() : _cond(_lock), _readers(0), _rlock(*this), _wlock(*this) {}
//! Destroy this ReadWriteLock
virtual ~FairReadWriteLock() {}
/**
* @see ReadWriteLock::getReadLock()
*/
virtual Lockable& getReadLock() { return _rlock; }
/**
* @see ReadWriteLock::getWriteLock()
*/
virtual Lockable& getWriteLock() { return _wlock; }
};
}; // __ZTFAIRREADWRITELOCK_H__
#endif
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