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/libpbd_visibility.h"
33 #include "pbd/failed_constructor.h"
38 Unnamed (process local) counting semaphore.
40 The civilized person's synchronisation primitive. A counting semaphore is
41 an integer which is always non-negative, so, an attempted decrement (or
42 "wait") will block if the value is 0, until another thread does an increment
45 At least on Lignux, the main advantage of this is that it is fast and the
46 only safe way to reliably signal from a real-time audio thread. The
47 counting semantics also complement ringbuffers of events nicely.
49 class LIBPBD_API Semaphore
53 Create a new semaphore.
55 Chances are you want 1 wait() per 1 post(), an initial value of 0.
57 inline Semaphore(unsigned initial);
61 /** Post/Increment/Signal */
64 /** Wait/Decrement. Returns false on error. */
67 /** Attempt Wait/Decrement. Returns true iff a decrement occurred. */
68 inline bool try_wait();
71 #if defined(__APPLE__)
72 semaphore_t _sem; // sem_t is a worthless broken mess on OSX
74 HANDLE _sem; // types are overrated anyway
83 Semaphore::Semaphore(unsigned initial)
85 if (semaphore_create(mach_task_self(), &_sem, SYNC_POLICY_FIFO, initial)) {
86 throw failed_constructor();
91 Semaphore::~Semaphore()
93 semaphore_destroy(mach_task_self(), _sem);
99 semaphore_signal(_sem);
105 if (semaphore_wait(_sem) != KERN_SUCCESS) {
112 Semaphore::try_wait()
114 const mach_timespec_t zero = { 0, 0 };
115 return semaphore_timedwait(_sem, zero) == KERN_SUCCESS;
118 #elif defined(_WIN32)
121 Semaphore::Semaphore(unsigned initial)
123 if (!(_sem = CreateSemaphore(NULL, initial, LONG_MAX, NULL))) {
124 throw failed_constructor();
129 Semaphore::~Semaphore()
137 ReleaseSemaphore(_sem, 1, NULL);
143 if (WaitForSingleObject(_sem, INFINITE) != WAIT_OBJECT_0) {
150 Semaphore::try_wait()
152 return WaitForSingleObject(_sem, 0) == WAIT_OBJECT_0;
155 #else /* !defined(__APPLE__) && !defined(_WIN32) */
157 Semaphore::Semaphore(unsigned initial)
159 if (sem_init(&_sem, 0, initial)) {
160 throw failed_constructor();
165 Semaphore::~Semaphore()
179 while (sem_wait(&_sem)) {
180 if (errno != EINTR) {
181 return false; // We are all doomed
183 /* Otherwise, interrupted (rare/weird), so try again. */
190 Semaphore::try_wait()
192 return (sem_trywait(&_sem) == 0);
199 #endif /* __pbd_semaphore_h__ */