This is a reimplementation of `semaphore-osx.c` from PulseAudio to use POSIX named semaphores. See [this bug](https://bugs.freedesktop.org/show_bug.cgi?id=63014). It is also used by the Homebrew PulseAudio formular, see [this report](https://github.com/mxcl/homebrew/pull/18838).

semaphore-osx.c

/***
  This file is part of PulseAudio.

  Copyright 2006 Lennart Poettering
  Copyright 2013 Albert Zeyer

  PulseAudio is free software; 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 2.1 of the License,
  or (at your option) any later version.

  PulseAudio 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
  General Public License for more details.

  You should have received a copy of the GNU Lesser General Public License
  along with PulseAudio; if not, write to the Free Software
  Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307
  USA.
***/

#ifdef HAVE_CONFIG_H
#include <config.h>
#endif

#include <stdio.h>
#include <errno.h>
#include <pthread.h>
#include <semaphore.h>
#include <sys/types.h>
#include <unistd.h>

#include <pulse/xmalloc.h>
#include <pulsecore/macro.h>
#include <pulsecore/atomic.h>
#include <pulsecore/core-util.h>

#include "semaphore.h"

/*
OSX doesn't support unnamed semaphores (via sem_init).
Thus, we use a counter to give them enumerated names.
*/

static pa_atomic_t id_counter = PA_ATOMIC_INIT(0);

struct pa_semaphore {
    sem_t* sem;
    int id;
};

static char *sem_name(char *fn, size_t l, int id) {
    pa_snprintf(fn, l, "/pulse-sem-%u-%u", getpid(), id);
    return fn;
}

pa_semaphore* pa_semaphore_new(unsigned value) {
    pa_semaphore *s;

    s = pa_xnew(pa_semaphore, 1);
    s->id = pa_atomic_inc(&id_counter);
    char fn[32]; sem_name(fn, sizeof(fn), s->id);
    sem_unlink(fn); // in case it already exists
    if((s->sem = sem_open(fn, O_CREAT|O_EXCL, 0700, value)) == SEM_FAILED) {
        perror("pa_semaphore_new: sem_open");
        abort();
    }
    return s;
}

void pa_semaphore_free(pa_semaphore *s) {
    pa_assert(s);
    pa_assert_se(sem_close(s->sem) == 0);
    char fn[32]; sem_name(fn, sizeof(fn), s->id);
    if(sem_unlink(fn) != 0)
        perror("pa_semaphore_free: sem_unlink");
    pa_xfree(s);
}

void pa_semaphore_post(pa_semaphore *s) {
    pa_assert(s);
    pa_assert_se(sem_post(s->sem) == 0);
}

void pa_semaphore_wait(pa_semaphore *s) {
    int ret;
    pa_assert(s);

    do {
        ret = sem_wait(s->sem);
    } while (ret < 0 && errno == EINTR);

    pa_assert(ret == 0);
}