merge 'lennart' branch back into trunk.

git-svn-id: file:///home/lennart/svn/public/pulseaudio/trunk@1971 fefdeb5f-60dc-0310-8127-8f9354f1896f

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);
+    }
+}
+