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wefts_rwmutex.h

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/*
   wefts_rwmutex.h
   Read/write Non Reentrant Mutex object header file.

   $Id: wefts_rwmutex.h,v 1.2 2003/08/05 15:40:20 jonnymind Exp $
---------------------------------------------
   Begin      : 2003-08-02 20:58
   Author     : Giancarlo Niccolai

   Last modified because:

*/

/**************************************************************************
*   This program is free software; you can redistribute it and/or modify  *
*   it under the terms of the GNU Library General Public License as       *
*   published by the Free Software Foundation; either version 2.1 of the  *
*   License, or (at your option) any later version.                       *
***************************************************************************/

#ifndef WT_RWMUTEX_H
#define WT_RWMUTEX_H

#ifdef __extern_c
extern "C" {
#endif

#include <pthread.h>

#ifdef __extern_c
}
#endif

#ifndef NO_ASSERTION
#include <cassert>
#endif

namespace Wefts {

class RWMutex
{
protected:
   pthread_mutex_t      m_mutex;
   pthread_cond_t       m_cond;
   volatile int m_lockCount;
   volatile int m_promCount;

public:
   RWMutex() {
      pthread_mutex_init( &m_mutex, NULL );
      pthread_cond_init( &m_cond, NULL );
      m_promCount = m_lockCount = 0;
   }

   ~RWMutex() {
      pthread_cond_destroy( &m_cond );
      pthread_mutex_destroy( &m_mutex );
   }

   virtual inline void lockRead()
   {
      pthread_mutex_lock( &m_mutex );
      while( m_lockCount < 0 ) {
         pthread_cond_wait( &m_cond, &m_mutex );
      }
      m_lockCount++;
      pthread_mutex_unlock( &m_mutex );
   }

   virtual inline void lockWrite()
   {
      pthread_mutex_lock( &m_mutex );
      while( m_lockCount != 0 ) {
         pthread_cond_wait( &m_cond, &m_mutex );
      }
      m_lockCount = -1;
      pthread_mutex_unlock( &m_mutex );
   }

   virtual inline void promote()
   {
      pthread_mutex_lock( &m_mutex );
      #ifndef NO_ASSERTIONS
      assert( m_lockCount > 0 );
      #endif
      m_promCount++;
      while( m_lockCount != m_promCount ) { // count if only this thread itself is left as reading.
         pthread_cond_wait( &m_cond, &m_mutex );
      }
      m_lockCount = -1;
      m_promCount --;
      pthread_mutex_unlock( &m_mutex );
   }

   virtual inline void unlock()
   {
      pthread_mutex_lock( &m_mutex );
      m_lockCount = m_lockCount > m_promCount ? m_lockCount-1: m_promCount;
      pthread_cond_broadcast( &m_cond );
      pthread_mutex_unlock( &m_mutex );
   }
};

}

#endif
/* end of wefts_rwmutex.h */

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