include/utilite/USemaphore.h

/*
*  utilite is a cross-platform library with
*  useful utilities for fast and small developing.
*  Copyright (C) 2010  Mathieu Labbe
*
*  utilite is free library: 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 3 of the License, or
*  (at your option) any later version.
*
*  utilite 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 program.  If not, see <http://www.gnu.org/licenses/>.
*/

/*
 * Originally written by Phillip Sitbon
 *  Copyright 2003
 */

#ifndef USEMAPHORE_H
#define USEMAPHORE_H

#include <errno.h>

#ifdef WIN32
#include "utilite/Win32/UWin32.h"
#define SEM_VALUE_MAX ((int) ((~0u) >> 1))
#else
#include <pthread.h>
#endif

class USemaphore
{
public:
        USemaphore( int initValue = 0 )
        {
#ifdef WIN32
                S = CreateSemaphore(0,initValue,SEM_VALUE_MAX,0);
#else
                _available = initValue;
                pthread_mutex_init(&_waitMutex, NULL);
                pthread_cond_init(&_cond, NULL);
#endif
        }

        virtual ~USemaphore()
        {
#ifdef WIN32
                CloseHandle(S);
#else
                pthread_cond_destroy(&_cond);
                pthread_mutex_destroy(&_waitMutex);
#endif
        }

#ifdef WIN32
        void acquire(int n = 1) const
        {
                while(n-- > 0)
                {
                        WaitForSingleObject((HANDLE)S,INFINITE);
                }
#else
        void acquire(int n = 1)
        {
                pthread_mutex_lock(&_waitMutex);
                while (n > _available)
                {
                        while(1)
                        {
                                pthread_cond_wait(&_cond, &_waitMutex);
                                break;
                        }
                }
                _available -= n;
                pthread_mutex_unlock(&_waitMutex);
#endif
        }

        /*
         * Try to acquire the semaphore, not a blocking call.
         * @return false if the semaphore can't be taken without waiting (value <= 0), true otherwise
         */
#ifdef WIN32
        int acquireTry() const
        {
                return ((WaitForSingleObject((HANDLE)S,INFINITE)==WAIT_OBJECT_0)?0:EAGAIN);
#else
        int acquireTry(int n)
        {
                pthread_mutex_lock(&_waitMutex);
                if(n > _available)
                {
                        pthread_mutex_unlock(&_waitMutex);
                        return false;
                }
                _available -= n;
                pthread_mutex_unlock(&_waitMutex);
                return true;
#endif
        }

#ifdef WIN32
        int release(int n = 1) const
        {
                return (ReleaseSemaphore((HANDLE)S,n,0)?0:ERANGE);
#else
        void release(int n = 1)
        {
                pthread_mutex_lock(&_waitMutex);
                _available += n;
                pthread_cond_broadcast(&_cond);
                pthread_mutex_unlock(&_waitMutex);
#endif
        }

#ifdef WIN32
        int value() const
        {
                LONG V = -1; ReleaseSemaphore((HANDLE)S,0,&V); return V;
#else
        int value()
        {
                int value = 0;
                pthread_mutex_lock(&_waitMutex);
                value = _available;
                pthread_mutex_unlock(&_waitMutex);
                return value;
#endif
        }

#ifdef WIN32
        /*
         * Reset the semaphore count.
         * @param init the initial value
         * TODO implement on posix ?
         */
        void reset( int init = 0 )
        {
                CloseHandle(S);
                S = CreateSemaphore(0,init,SEM_VALUE_MAX,0);
        }
#endif

private:
#ifdef WIN32
        HANDLE S;
#else
        pthread_mutex_t _waitMutex;
        pthread_cond_t _cond;
        int _available;
#endif
        void operator=(const USemaphore &S){}
        USemaphore(const USemaphore &S){}
};

#endif // USEMAPHORE_H