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>
25 #elif defined(PLATFORM_WINDOWS)
28 #define INFINITE 0xffffffffL
31 # include <semaphore.h>
35 #include "pbd/failed_constructor.h"
40 Unnamed (process local) counting semaphore.
42 The civilized person's synchronisation primitive. A counting semaphore is
43 an integer which is always non-negative, so, an attempted decrement (or
44 "wait") will block if the value is 0, until another thread does an increment
47 At least on Lignux, the main advantage of this is that it is fast and the
48 only safe way to reliably signal from a real-time audio thread. The
49 counting semantics also complement ringbuffers of events nicely.
55 Create a new semaphore.
57 Chances are you want 1 wait() per 1 post(), an initial value of 0.
59 inline Semaphore(unsigned initial);
63 /** Post/Increment/Signal */
66 /** Wait/Decrement. Returns false on error. */
69 /** Attempt Wait/Decrement. Returns true iff a decrement occurred. */
70 inline bool try_wait();
73 #if defined(__APPLE__)
74 semaphore_t _sem; // sem_t is a worthless broken mess on OSX
75 #elif defined(PLATFORM_WINDOWS)
76 HANDLE _sem; // types are overrated anyway
85 Semaphore::Semaphore(unsigned initial)
87 if (semaphore_create(mach_task_self(), &_sem, SYNC_POLICY_FIFO, initial)) {
88 throw failed_constructor();
93 Semaphore::~Semaphore()
95 semaphore_destroy(mach_task_self(), _sem);
101 semaphore_signal(_sem);
107 if (semaphore_wait(_sem) != KERN_SUCCESS) {
114 Semaphore::try_wait()
116 const mach_timespec_t zero = { 0, 0 };
117 return semaphore_timedwait(_sem, zero) == KERN_SUCCESS;
120 #elif defined(PLATFORM_WINDOWS)
123 Semaphore::Semaphore(unsigned initial)
125 if (!(_sem = CreateSemaphore(NULL, initial, LONG_MAX, NULL))) {
126 throw failed_constructor();
131 Semaphore::~Semaphore()
139 ReleaseSemaphore(_sem, 1, NULL);
145 if (WaitForSingleObject(_sem, INFINITE) != WAIT_OBJECT_0) {
152 Semaphore::try_wait()
154 return WaitForSingleObject(_sem, 0) == WAIT_OBJECT_0;
157 #else /* !defined(__APPLE__) && !defined(PLATFORM_WINDOWS) */
159 Semaphore::Semaphore(unsigned initial)
161 if (sem_init(&_sem, 0, initial)) {
162 throw failed_constructor();
167 Semaphore::~Semaphore()
181 while (sem_wait(&_sem)) {
182 if (errno != EINTR) {
183 return false; // We are all doomed
185 /* Otherwise, interrupted (rare/weird), so try again. */
192 Semaphore::try_wait()
194 return (sem_trywait(&_sem) == 0);
201 #endif /* __pbd_semaphore_h__ */