rw_lock.h

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/** @file
 *  @author Bram de Greve (bram@cocamware.com)
 *  @author Tom De Muer (tom@cocamware.com)
 *
 *  *** BEGIN LICENSE INFORMATION ***
 *  
 *  The contents of this file are subject to the Common Public Attribution License 
 *  Version 1.0 (the "License"); you may not use this file except in compliance with 
 *  the License. You may obtain a copy of the License at 
 *  http://lass.sourceforge.net/cpal-license. The License is based on the 
 *  Mozilla Public License Version 1.1 but Sections 14 and 15 have been added to cover 
 *  use of software over a computer network and provide for limited attribution for 
 *  the Original Developer. In addition, Exhibit A has been modified to be consistent 
 *  with Exhibit B.
 *  
 *  Software distributed under the License is distributed on an "AS IS" basis, WITHOUT 
 *  WARRANTY OF ANY KIND, either express or implied. See the License for the specific 
 *  language governing rights and limitations under the License.
 *  
 *  The Original Code is LASS - Library of Assembled Shared Sources.
 *  
 *  The Initial Developer of the Original Code is Bram de Greve and Tom De Muer.
 *  The Original Developer is the Initial Developer.
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#ifndef LASS_GUARDIAN_OF_INCLUSION_UTIL_RW_LOCK_H
#define LASS_GUARDIAN_OF_INCLUSION_UTIL_RW_LOCK_H
 
#include "util_common.h"
#include "atomic.h"
#include "thread.h" 
 
namespace lass
{
namespace util
{
 
namespace impl
{
} //namespace impl
 
 
/** Lean and mean synchronisation object, without OS support.
*   @ingroup Threading
*   @see RWLocker
*   @author Tom De Muer
*   @date 2006
*   
*   This lock is built upon atomic operations that are programmed in assembly.  It makes a difference
*   between reading and writing.  A maximum number of readers is allowed while only 1 writer is allowed.
*   The writer will only enter if there are no readers are reading at the same moment.  This RWLock is 
*   a blocking and spinning synchronization object.  Priority is given over writers, as soon as a writer is
*   trying to enter, only one subsequent reader will in worst case be able to enter.
*/
 
class LASS_DLL RWLock : NonCopyable
{
 
public:
    RWLock(int iMaxReaders);
    ~RWLock();
 
    void lockr();
    void lockw();
    void unlockr();
    void unlockw();
 
    LockResult tryLockr();
    LockResult tryLockw();
 
private:
    const int maxReaders_;      /**< the maximum of simultaneous readers allowed */
    std::atomic<int> spinLock_;
    std::atomic<int> writersTrying_;        /**< the number of writers trying to enter */
};
 
} //namespace util
} //namespace lass
 
 
#endif
 
// EOF