2 Copyright (C) 2012 Paul Davis
3 Author: David Robillard
5 This program is free software; you can redistribute it and/or modify
6 it under the terms of the GNU General Public License as published by
7 the Free Software Foundation; either version 2 of the License, or
8 (at your option) any later version.
10 This program is distributed in the hope that it will be useful,
11 but WITHOUT ANY WARRANTY; without even the implied warranty of
12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
13 GNU General Public License for more details.
15 You should have received a copy of the GNU General Public License
16 along with this program; if not, write to the Free Software
17 Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
20 #ifndef __pbd_semaphore_h__
21 #define __pbd_semaphore_h__
24 # include <mach/mach.h>
28 # include <semaphore.h>
32 #include "pbd/failed_constructor.h"
37 Unnamed (process local) counting semaphore.
39 The civilized person's synchronisation primitive. A counting semaphore is
40 an integer which is always non-negative, so, an attempted decrement (or
41 "wait") will block if the value is 0, until another thread does an increment
44 At least on Lignux, the main advantage of this is that it is fast and the
45 only safe way to reliably signal from a real-time audio thread. The
46 counting semantics also complement ringbuffers of events nicely.
52 Create a new semaphore.
54 Chances are you want 1 wait() per 1 post(), an initial value of 0.
56 inline Semaphore(unsigned initial);
60 /** Post/Increment/Signal */
63 /** Wait/Decrement. Returns false on error. */
66 /** Attempt Wait/Decrement. Returns true iff a decrement occurred. */
67 inline bool try_wait();
70 #if defined(__APPLE__)
71 semaphore_t _sem; // sem_t is a worthless broken mess on OSX
73 HANDLE _sem; // types are overrated anyway
82 Semaphore::Semaphore(unsigned initial)
84 if (semaphore_create(mach_task_self(), &_sem, SYNC_POLICY_FIFO, initial)) {
85 throw failed_constructor();
90 Semaphore::~Semaphore()
92 semaphore_destroy(mach_task_self(), _sem);
98 semaphore_signal(_sem);
104 if (semaphore_wait(_sem) != KERN_SUCCESS) {
111 Semaphore::try_wait()
113 const mach_timespec_t zero = { 0, 0 };
114 return semaphore_timedwait(_sem, zero) == KERN_SUCCESS;
117 #elif defined(_WIN32)
120 Semaphore::Semaphore(unsigned initial)
122 if (!(_sem = CreateSemaphore(NULL, initial, LONG_MAX, NULL))) {
123 throw failed_constructor();
128 Semaphore::~Semaphore()
136 ReleaseSemaphore(_sem, 1, NULL);
142 if (WaitForSingleObject(_sem, INFINITE) != WAIT_OBJECT_0) {
149 Semaphore::try_wait()
151 return WaitForSingleObject(_sem, 0) == WAIT_OBJECT_0;
154 #else /* !defined(__APPLE__) && !defined(_WIN32) */
156 Semaphore::Semaphore(unsigned initial)
158 if (sem_init(&_sem, 0, initial)) {
159 throw failed_constructor();
164 Semaphore::~Semaphore()
178 while (sem_wait(&_sem)) {
179 if (errno != EINTR) {
180 return false; // We are all doomed
182 /* Otherwise, interrupted (rare/weird), so try again. */
189 Semaphore::try_wait()
191 return (sem_trywait(&_sem) == 0);
198 #endif /* __pbd_semaphore_h__ */