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-rw-r--r--src/pulsecore/once.c96
1 files changed, 96 insertions, 0 deletions
diff --git a/src/pulsecore/once.c b/src/pulsecore/once.c
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index 00000000..a358cf65
--- /dev/null
+++ b/src/pulsecore/once.c
@@ -0,0 +1,96 @@
+/* $Id$ */
+
+/***
+ This file is part of PulseAudio.
+
+ Copyright 2006 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 <pulsecore/macro.h>
+#include <pulsecore/mutex.h>
+
+#include "once.h"
+
+int pa_once_begin(pa_once *control) {
+ pa_mutex *m;
+
+ pa_assert(control);
+
+ if (pa_atomic_load(&control->done))
+ return 0;
+
+ pa_atomic_inc(&control->ref);
+
+ /* Caveat: We have to make sure that the once func has completed
+ * before returning, even if the once func is not actually
+ * executed by us. Hence the awkward locking. */
+
+ for (;;) {
+
+ if ((m = pa_atomic_ptr_load(&control->mutex))) {
+
+ /* The mutex is stored in locked state, hence let's just
+ * wait until it is unlocked */
+ pa_mutex_lock(m);
+
+ pa_once_end(control);
+ return 0;
+ }
+
+ pa_assert_se(m = pa_mutex_new(FALSE, FALSE));
+ pa_mutex_lock(m);
+
+ if (pa_atomic_ptr_cmpxchg(&control->mutex, NULL, m))
+ return 1;
+
+ pa_mutex_unlock(m);
+ pa_mutex_free(m);
+ }
+}
+
+void pa_once_end(pa_once *control) {
+ pa_mutex *m;
+
+ pa_assert(control);
+
+ pa_atomic_store(&control->done, 1);
+
+ pa_assert_se(m = pa_atomic_ptr_load(&control->mutex));
+ pa_mutex_unlock(m);
+
+ if (pa_atomic_dec(&control->ref) <= 1) {
+ pa_assert_se(pa_atomic_ptr_cmpxchg(&control->mutex, m, NULL));
+ pa_mutex_free(m);
+ }
+}
+
+/* Not reentrant -- how could it be? */
+void pa_run_once(pa_once *control, pa_once_func_t func) {
+ pa_assert(control);
+ pa_assert(func);
+
+ if (pa_once_begin(control)) {
+ func();
+ pa_once_end(control);
+ }
+}
+