---

wefts_rrwmutex.h

Go to the documentation of this file.

/*
   wefts_rrwmutex.h
   Read/write Reentrant/advanced Mutex object header file.

   $Id: wefts_rrwmutex.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_RRWMUTEX_H
#define WT_RRWMUTEX_H

#include <wefts_rwmutex.h>
#ifndef NO_ASSERTIONS
#include <cassert>
#endif

namespace Wefts {

class RRWMutex: public RWMutex  {
private:
   volatile int m_fence;
   pthread_t m_owner;

public:
   RRWMutex(): RWMutex() {
      m_fence = 0;
      m_owner = 0;
   }

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

   virtual inline void promote( bool fence )
   {
      volatile pthread_t thid = pthread_self();
      pthread_mutex_lock( &m_mutex );
      #ifndef NO_ASSERTIONS
      assert( m_lockCount > 0 );
      #endif
      m_promCount++;
      if ( fence ) m_fence ++;
      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_owner = thid;
      // I can release my fence, as reading threads are now blocked by
      //  the write lock, but I cannot set it to 0: other write lockers
      //  could have issued a fence before I had this lock.
      if (fence) m_fence--;
      m_promCount--;
      pthread_mutex_unlock( &m_mutex );
   }

   virtual void inline promote() { promote( false ); }

   virtual inline void lockWrite( bool fence )
   {
      volatile pthread_t thid = pthread_self();
      pthread_mutex_lock( &m_mutex );
      if ( fence ) m_fence ++;
      while( m_lockCount > 0 || ( m_owner != thid && m_owner != 0)) {
         pthread_cond_wait( &m_cond, &m_mutex );
      }
      m_lockCount--;
      m_owner = thid;
      // I can release my fence, as reading threads are now blocked by
      //  the write lock, but I cannot set it to 0: other write lockers
      //  could have issued a fence before I had this lock.
      if (fence) m_fence--;
      pthread_mutex_unlock( &m_mutex );
   }

   virtual inline void lockWrite() { lockWrite( false ); }

   virtual inline void unlock()
   {
      pthread_mutex_lock( &m_mutex );
      if ( m_lockCount > 0 ) {
         m_lockCount --;
         if ( m_lockCount == m_promCount )
            pthread_cond_broadcast( &m_cond );
      }
      else {
         if ( m_owner == pthread_self() ) {
            m_lockCount++;
            if ( m_lockCount == 0 ) {
               m_owner = 0;
               m_lockCount = m_promCount;
               pthread_cond_broadcast( &m_cond );
            }
         }
      }
      pthread_mutex_unlock( &m_mutex );
   }
};

}

#endif
/* end of wefts_rrwmutex.h */

---