1 files changed, 75 insertions, 0 deletions
diff --git a/src/pulsecore/once.c b/src/pulsecore/once.c
new file mode 100644
index 0000000..6e52801
--- /dev/null
+++ b/src/pulsecore/once.c
@@ -0,0 +1,75 @@
+/***
+  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 2.1 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, see <http://www.gnu.org/licenses/>.
+***/
+
+#ifdef HAVE_CONFIG_H
+#include <config.h>
+#endif
+
+#include <pulsecore/macro.h>
+
+#include "once.h"
+
+/* See http://www.hpl.hp.com/research/linux/atomic_ops/example.php4 for the
+ * reference algorithm used here. */
+
+bool pa_once_begin(pa_once *control) {
+    pa_mutex *m;
+
+    pa_assert(control);
+
+    if (pa_atomic_load(&control->done))
+        return false;
+
+    /* 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. */
+
+    m = pa_static_mutex_get(&control->mutex, false, false);
+    pa_mutex_lock(m);
+
+    if (pa_atomic_load(&control->done)) {
+        pa_mutex_unlock(m);
+        return false;
+    }
+
+    return true;
+}
+
+void pa_once_end(pa_once *control) {
+    pa_mutex *m;
+
+    pa_assert(control);
+
+    pa_assert(!pa_atomic_load(&control->done));
+    pa_atomic_store(&control->done, 1);
+
+    m = pa_static_mutex_get(&control->mutex, false, false);
+    pa_mutex_unlock(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);
+    }
+}