PthreadReadWriteLock.cc

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//=============================================================================
//  PthreadReadWriteLock and protection classes
//-----------------------------------------------------------------------------
//  POSIX Pthread class library
//  Copyright (C) 1997-1999  The University of Texas
//
//  This library 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 of the License, or
//  (at your option) any later version.
//
//  This library is distributed in the hope that it will be useful,
//  but WITHOUT ANY WARRANTY; without even the implied warranty of
//  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
//  Library General Public License for more details.
//
//  The GNU Public License is available in the file LICENSE, or you
//  can write to the Free Software Foundation, Inc., 59 Temple Place -
//  Suite 330, Boston, MA 02111-1307, USA, or you can find it on the
//  World Wide Web at http://www.fsf.org.
//=============================================================================


#include <cpn/threading/PthreadReadWriteLock.h>
#ifdef _POSIX_THREADS


//-----------------------------------------------------------------------------
PthreadReadWriteLock::PthreadReadWriteLock(int _priorityWrites)
//-----------------------------------------------------------------------------
:   numReaders(0),
    writing(0),
    noNewReaders(0),
    priorityWrites(_priorityWrites)
//  mutex(), lockFree()
{
}


//-----------------------------------------------------------------------------
void PthreadReadWriteLock::ReadLock(void)
//-----------------------------------------------------------------------------
{
    PthreadMutexProtected protect(mutex);
    while (noNewReaders)
        lockFree.Wait(mutex);
    numReaders++;
}


//-----------------------------------------------------------------------------
void PthreadReadWriteLock::WriteLock(void)
//-----------------------------------------------------------------------------
{
    PthreadMutexProtected protect(mutex);
    if (priorityWrites)
        noNewReaders = 1;
    while (writing || numReaders)
        lockFree.Wait(mutex);
    writing++;
    noNewReaders = 1;
}


//-----------------------------------------------------------------------------
void PthreadReadWriteLock::ReadUnlock(void)
//-----------------------------------------------------------------------------
{
    PthreadMutexProtected protect(mutex);

    if (numReaders<=0) {
        TrapError(-1);
        return;
    }

    numReaders--;
    if (!numReaders)
        lockFree.Signal();
}


//-----------------------------------------------------------------------------
void PthreadReadWriteLock::WriteUnlock(void)
//-----------------------------------------------------------------------------
{
    PthreadMutexProtected protect(mutex);

    if (!writing) {
        TrapError(-1);
        return;
    }
    
    writing = 0;
    noNewReaders = 0;
    lockFree.Broadcast();
}


#endif