implement trival pa_once API based on atomic operations

git-svn-id: file:///home/lennart/svn/public/pulseaudio/trunk@1385 fefdeb5f-60dc-0310-8127-8f9354f1896f

src/pulsecore/once.h

@@ -0,0 +1,42 @@
+#ifndef foopulseoncehfoo
+#define foopulseoncehfoo
+
+/* $Id$ */
+
+/***
+  This file is part of PulseAudio.
+ 
+  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.
+***/
+
+#include <pulsecore/atomic.h>
+
+typedef struct pa_once {
+    pa_atomic_int_t atomic;
+} pa_once_t;
+
+#define PA_ONCE_INIT { PA_ATOMIC_INIT(0) }
+
+#define pa_once_test(o) (pa_atomic_cmpxchg(&(o)->atomic, 0, 1))
+
+typedef void (*pa_once_func_t) (void);
+
+static inline void pa_once(pa_once_t *o, pa_once_func_t f) {
+    if (pa_once_test(o))
+        f();
+}
+
+#endif