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/*
Copyright (c) 2007-2009 FastMQ Inc.
This file is part of 0MQ.
0MQ is free software; you can redistribute it and/or modify it under
the terms of the Lesser GNU General Public License as published by
the Free Software Foundation; either version 3 of the License, or
(at your option) any later version.
0MQ 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
Lesser GNU General Public License for more details.
You should have received a copy of the Lesser GNU General Public License
along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
#ifndef __ZMQ_SIMPLE_SEMAPHORE_HPP_INCLUDED__
#define __ZMQ_SIMPLE_SEMAPHORE_HPP_INCLUDED__
#include "platform.hpp"
#include "err.hpp"
#if 0 //defined ZMQ_HAVE_LINUX
#include <sys/syscall.h>
#include <unistd.h>
#include <linux/futex.h>
#elif defined ZMQ_HAVE_LINUX ||defined ZMQ_HAVE_OSX || defined ZMQ_HAVE_OPENVMS
#include <pthread.h>
#elif defined ZMQ_HAVE_WINDOWS
#include "windows.hpp"
#else
#include <semaphore.h>
#endif
namespace zmq
{
// Simple semaphore. Only single thread may be waiting at any given time.
// Also, the semaphore may not be posted before the previous post
// was matched by corresponding wait and the waiting thread was
// released.
#if 0 //defined ZMQ_HAVE_LINUX
// In theory, using private futexes should be more efficient on Linux
// platform than using mutexes. However, in uncontended cases of TCP
// transport on loopback interface we haven't seen any latency improvement.
// The code is commented out waiting for more thorough testing.
class simple_semaphore_t
{
public:
// Initialise the semaphore.
inline simple_semaphore_t () :
dummy (0)
{
}
// Destroy the semaphore.
inline ~simple_semaphore_t ()
{
}
// Wait for the semaphore.
inline void wait ()
{
int rc = syscall (SYS_futex, &dummy, (int) FUTEX_WAIT_PRIVATE,
(int) 0, NULL, NULL, (int) 0);
zmq_assert (rc == 0);
}
// Post the semaphore.
inline void post ()
{
while (true) {
int rc = syscall (SYS_futex, &dummy, (int) FUTEX_WAKE_PRIVATE,
(int) 1, NULL, NULL, (int) 0);
zmq_assert (rc != -1 && rc <= 1);
if (rc == 1)
break;
}
}
private:
int dummy;
// Disable copying of the object.
simple_semaphore_t (const simple_semaphore_t&);
void operator = (const simple_semaphore_t&);
};
#elif defined ZMQ_HAVE_LINUX || defined ZMQ_HAVE_OSX || defined ZMQ_HAVE_OPENVMS
// On platforms that allow for double locking of a mutex from the same
// thread, simple semaphore is implemented using mutex, as it is more
// efficient than full-blown semaphore.
class simple_semaphore_t
{
public:
// Initialise the semaphore.
inline simple_semaphore_t ()
{
int rc = pthread_mutex_init (&mutex, NULL);
posix_assert (rc);
rc = pthread_mutex_lock (&mutex);
posix_assert (rc);
}
// Destroy the semaphore.
inline ~simple_semaphore_t ()
{
int rc = pthread_mutex_unlock (&mutex);
posix_assert (rc);
rc = pthread_mutex_destroy (&mutex);
posix_assert (rc);
}
// Wait for the semaphore.
inline void wait ()
{
int rc = pthread_mutex_lock (&mutex);
posix_assert (rc);
}
// Post the semaphore.
inline void post ()
{
int rc = pthread_mutex_unlock (&mutex);
posix_assert (rc);
}
private:
pthread_mutex_t mutex;
// Disable copying of the object.
simple_semaphore_t (const simple_semaphore_t&);
void operator = (const simple_semaphore_t&);
};
#elif defined ZMQ_HAVE_WINDOWS
// On Windows platform simple semaphore is implemeted using event object.
class simple_semaphore_t
{
public:
// Initialise the semaphore.
inline simple_semaphore_t ()
{
ev = CreateEvent (NULL, FALSE, FALSE, NULL);
win_assert (ev != NULL);
}
// Destroy the semaphore.
inline ~simple_semaphore_t ()
{
int rc = CloseHandle (ev);
win_assert (rc != 0);
}
// Wait for the semaphore.
inline void wait ()
{
DWORD rc = WaitForSingleObject (ev, INFINITE);
win_assert (rc != WAIT_FAILED);
}
// Post the semaphore.
inline void post ()
{
int rc = SetEvent (ev);
win_assert (rc != 0);
}
private:
HANDLE ev;
// Disable copying of the object.
simple_semaphore_t (const simple_semaphore_t&);
void operator = (const simple_semaphore_t&);
};
#else
// Default implementation maps simple semaphore to standard semaphore.
class simple_semaphore_t
{
public:
// Initialise the semaphore.
inline simple_semaphore_t ()
{
int rc = sem_init (&sem, 0, 0);
errno_assert (rc != -1);
}
// Destroy the semaphore.
inline ~simple_semaphore_t ()
{
int rc = sem_destroy (&sem);
errno_assert (rc != -1);
}
// Wait for the semaphore.
inline void wait ()
{
int rc = sem_wait (&sem);
errno_assert (rc != -1);
}
// Post the semaphore.
inline void post ()
{
int rc = sem_post (&sem);
errno_assert (rc != -1);
}
private:
// Underlying system semaphore object.
sem_t sem;
// Disable copying of the object.
simple_semaphore_t (const simple_semaphore_t&);
void operator = (const simple_semaphore_t&);
};
#endif
}
#endif
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