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-rw-r--r--src/pulsecore/lock-autospawn.c330
1 files changed, 330 insertions, 0 deletions
diff --git a/src/pulsecore/lock-autospawn.c b/src/pulsecore/lock-autospawn.c
new file mode 100644
index 00000000..d36b669e
--- /dev/null
+++ b/src/pulsecore/lock-autospawn.c
@@ -0,0 +1,330 @@
+/***
+ This file is part of PulseAudio.
+
+ Copyright 2008 Lennart Poettering
+
+ 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 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 <fcntl.h>
+#include <errno.h>
+#include <string.h>
+#include <sys/poll.h>
+#include <signal.h>
+#include <pthread.h>
+
+#include <pulse/i18n.h>
+#include <pulse/xmalloc.h>
+
+#include <pulsecore/mutex.h>
+#include <pulsecore/thread.h>
+#include <pulsecore/core-util.h>
+
+#include "lock-autospawn.h"
+
+/* So, why do we have this complex code here with threads and pipes
+ * and stuff? For two reasons: POSIX file locks are per-process, not
+ * per-file descriptor. That means that two contexts within the same
+ * process that try to create the autospawn lock might end up assuming
+ * they both managed to lock the file. And then, POSIX locking
+ * operations are synchronous. If two contexts run from the same event
+ * loop it must be made sure that they do not block each other, but
+ * that the locking operation can happen asynchronously. */
+
+#define AUTOSPAWN_LOCK "autospawn.lock"
+
+static pa_mutex *mutex;
+
+static unsigned n_ref = 0;
+static int lock_fd = -1;
+static pa_mutex *lock_fd_mutex = NULL;
+static pa_bool_t taken = FALSE;
+static pa_thread *thread;
+static int pipe_fd[2] = { -1, -1 };
+
+static void destroy_mutex(void) PA_GCC_DESTRUCTOR;
+
+static int ref(void) {
+
+ if (n_ref > 0) {
+
+ pa_assert(pipe_fd[0] >= 0);
+ pa_assert(pipe_fd[1] >= 0);
+
+ n_ref++;
+
+ return 0;
+ }
+
+ pa_assert(lock_fd < 0);
+ pa_assert(!lock_fd_mutex);
+ pa_assert(!taken);
+ pa_assert(!thread);
+ pa_assert(pipe_fd[0] < 0);
+ pa_assert(pipe_fd[1] < 0);
+
+ if (pipe(pipe_fd) < 0)
+ return -1;
+
+ lock_fd_mutex = pa_mutex_new(FALSE, FALSE);
+
+ pa_make_fd_cloexec(pipe_fd[0]);
+ pa_make_fd_cloexec(pipe_fd[1]);
+
+ pa_make_fd_nonblock(pipe_fd[1]);
+ pa_make_fd_nonblock(pipe_fd[0]);
+
+ n_ref = 1;
+ return 0;
+}
+
+static void unref(pa_bool_t after_fork) {
+
+ pa_assert(n_ref > 0);
+ pa_assert(pipe_fd[0] >= 0);
+ pa_assert(pipe_fd[1] >= 0);
+ pa_assert(lock_fd_mutex);
+
+ n_ref--;
+
+ if (n_ref > 0)
+ return;
+
+ pa_assert(!taken);
+
+ if (thread) {
+ pa_thread_free(thread);
+ thread = NULL;
+ }
+
+ pa_mutex_lock(lock_fd_mutex);
+ if (lock_fd >= 0) {
+
+ if (after_fork)
+ pa_close(lock_fd);
+ else {
+ char *lf;
+
+ if (!(lf = pa_runtime_path(AUTOSPAWN_LOCK)))
+ pa_log_warn(_("Cannot access autospawn lock."));
+
+ pa_unlock_lockfile(lf, lock_fd);
+ pa_xfree(lf);
+
+ lock_fd = -1;
+ }
+ }
+ pa_mutex_unlock(lock_fd_mutex);
+
+ pa_mutex_free(lock_fd_mutex);
+ lock_fd_mutex = NULL;
+
+ pa_close(pipe_fd[0]);
+ pa_close(pipe_fd[1]);
+ pipe_fd[0] = pipe_fd[1] = -1;
+}
+
+static void ping(void) {
+ ssize_t s;
+
+ pa_assert(pipe_fd[1] >= 0);
+
+ for (;;) {
+ char x = 'x';
+
+ if ((s = write(pipe_fd[1], &x, 1)) == 1)
+ break;
+
+ pa_assert(s < 0);
+
+ if (errno == EAGAIN)
+ break;
+
+ pa_assert(errno == EINTR);
+ }
+}
+
+static void wait_for_ping(void) {
+ ssize_t s;
+ char x;
+ struct pollfd pfd;
+ int k;
+
+ pa_assert(pipe_fd[0] >= 0);
+
+ memset(&pfd, 0, sizeof(pfd));
+ pfd.fd = pipe_fd[0];
+ pfd.events = POLLIN;
+
+ if ((k = poll(&pfd, 1, -1)) != 1) {
+ pa_assert(k < 0);
+ pa_assert(errno == EINTR);
+ } else if ((s = read(pipe_fd[0], &x, 1)) != 1) {
+ pa_assert(s < 0);
+ pa_assert(errno == EAGAIN);
+ }
+}
+
+static void empty_pipe(void) {
+ char x[16];
+ ssize_t s;
+
+ pa_assert(pipe_fd[0] >= 0);
+
+ if ((s = read(pipe_fd[0], &x, sizeof(x))) < 1) {
+ pa_assert(s < 0);
+ pa_assert(errno == EAGAIN);
+ }
+}
+
+static void thread_func(void *u) {
+ int fd;
+ char *lf;
+ sigset_t fullset;
+
+ /* No signals in this thread please */
+ sigfillset(&fullset);
+ pthread_sigmask(SIG_BLOCK, &fullset, NULL);
+
+ if (!(lf = pa_runtime_path(AUTOSPAWN_LOCK))) {
+ pa_log_warn(_("Cannot access autospawn lock."));
+ goto finish;
+ }
+
+ if ((fd = pa_lock_lockfile(lf)) < 0)
+ goto finish;
+
+ pa_mutex_lock(lock_fd_mutex);
+ pa_assert(lock_fd < 0);
+ lock_fd = fd;
+ pa_mutex_unlock(lock_fd_mutex);
+
+finish:
+ pa_xfree(lf);
+
+ ping();
+}
+
+static int start_thread(void) {
+
+ if (!thread)
+ if (!(thread = pa_thread_new(thread_func, NULL)))
+ return -1;
+
+ return 0;
+}
+
+static void create_mutex(void) {
+ PA_ONCE_BEGIN {
+ mutex = pa_mutex_new(FALSE, FALSE);
+ } PA_ONCE_END;
+}
+
+static void destroy_mutex(void) {
+
+ if (mutex)
+ pa_mutex_free(mutex);
+}
+
+
+int pa_autospawn_lock_init(void) {
+ int ret = -1;
+
+ create_mutex();
+ pa_mutex_lock(mutex);
+
+ if (ref() < 0)
+ ret = -1;
+ else
+ ret = pipe_fd[0];
+
+ pa_mutex_unlock(mutex);
+
+ return ret;
+}
+
+int pa_autospawn_lock_acquire(pa_bool_t block) {
+ int ret = -1;
+
+ create_mutex();
+ pa_mutex_lock(mutex);
+ pa_assert(n_ref >= 1);
+
+ pa_mutex_lock(lock_fd_mutex);
+
+ for (;;) {
+
+ empty_pipe();
+
+ if (lock_fd >= 0 && !taken) {
+ taken = TRUE;
+ ret = 1;
+ break;
+ }
+
+ if (lock_fd < 0)
+ if (start_thread() < 0)
+ break;
+
+ if (!block) {
+ ret = 0;
+ break;
+ }
+
+ pa_mutex_unlock(lock_fd_mutex);
+ pa_mutex_unlock(mutex);
+
+ wait_for_ping();
+
+ pa_mutex_lock(mutex);
+ pa_mutex_lock(lock_fd_mutex);
+ }
+
+ pa_mutex_unlock(lock_fd_mutex);
+
+ pa_mutex_unlock(mutex);
+
+ return ret;
+}
+
+void pa_autospawn_lock_release(void) {
+
+ create_mutex();
+ pa_mutex_lock(mutex);
+ pa_assert(n_ref >= 1);
+
+ pa_assert(taken);
+ taken = FALSE;
+
+ ping();
+
+ pa_mutex_unlock(mutex);
+}
+
+void pa_autospawn_lock_done(pa_bool_t after_fork) {
+
+ create_mutex();
+ pa_mutex_lock(mutex);
+ pa_assert(n_ref >= 1);
+
+ unref(after_fork);
+
+ pa_mutex_unlock(mutex);
+}