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s3_semaphore.cc

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/*
 * Stone Three Foundation Class (s3fc) provides a number of utility classes.
 * Copyright (C) 2001 by Stone Three Signal Processing (Pty) Ltd.
 *
 * Authored by Stone Three Signal Processing (Pty) Ltd.
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2.1 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
 * Lesser General Public License for more details.
 * 
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 * 
 * Please see the file 'COPYING' in the source root directory.
 */

#include <pthread.h>
#include <s3fc/s3_semaphore.h>
#include <s3fc/s3_exception.h>

#ifndef CONST_OVERRIDE_SEM_T
#define CONST_OVERRIDE_SEM_T(x) const_cast<sem_t*>(x)
#endif

// init semaphore
s3_semaphore::s3_semaphore(int n_value)
{
   if ( sem_init(&sem, 0, n_value) != 0 )
   {
      throw s3_generic_exception("s3_semaphore::s3_semaphore(int n_value)",
                                 "sem_init() failed - n_value out of range");
   }
}

// destroy semaphore
s3_semaphore::~s3_semaphore()
{
   if ( sem_destroy(&sem) != 0 )
   {
      throw s3_generic_exception("s3_semaphore::~s3_semaphore()",
                                 "Attempted to destroy semaphore with threads"
                                 " waiting on it.");
   }
}

// this should NEVER be called
s3_semaphore::s3_semaphore(const s3_semaphore& src)
{
   throw s3_generic_exception("s3_semaphore::s3_semaphore(const s3_semaphore&)",
                              "Function should *never* be called.");
}

// this should NEVER be called
s3_semaphore& s3_semaphore::operator=(const s3_semaphore& src)
{
   throw s3_generic_exception("s3_semaphore::operator=(const s3_semaphore&)",
                              "Function should *never* be called.");
}

// call sem_wait
void s3_semaphore::wait() const
{
   sem_wait(CONST_OVERRIDE_SEM_T(&sem));
}

// forward to sem_trywait an return true if it succeeds
bool s3_semaphore::try_wait() const
{
   bool rv = ( sem_trywait(CONST_OVERRIDE_SEM_T(&sem)) == 0 );
   return rv;
}

// forward to sem_post and throw if it fails
void s3_semaphore::post() const
{
   if ( sem_post(CONST_OVERRIDE_SEM_T(&sem)) != 0 )
   {
      throw s3_generic_exception("s3_semaphore::post() const",
                                 "Attempted to increment semaphore value"
                                 " past SEM_VALUE_MAX.");
   }
}

// forward to sem_getvalue
int s3_semaphore::get_value() const
{
   int val = 0;

#if _WIN32
   /*
    * sem_getvalue is broken on win2k.
    * The pthreads WIN32 api use the ReleaseSemaphore call with 
    * lReleaseCount = 0. However, according the the WIN32 docs, the
    * value of lReleaseCount must be larger than zero.
    * Therefore, the call works on Win9x but not on WinNT/2k.
    *
    * 30 May 2002: Jan Pool <jpool@stonethree.com>
    */
   
   /*
    * We use sem_trywait() to determine the current count and then
    * use sem_post() to put them back.
    *
    * Very inefficient, but will have to do for now.
    */
    while ( sem_trywait( CONST_OVERRIDE_SEM_T(&sem) ) == 0)
    {
      val++;
    }
    int cnt = val;
    while( cnt-- )
    {
       sem_post( CONST_OVERRIDE_SEM_T(&sem) );
    }     
#else
   sem_getvalue(CONST_OVERRIDE_SEM_T(&sem), &val);
#endif

   return val;
}

// while try_wait
void s3_semaphore::flush() const
{
   while ( try_wait() );
}

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