rework pa_once once again, because the once function needs to have terminated before pa_once returns, regardless whether the local call executes it or another thread does.

With the previous code it might happen that an long-running initializing in a once function is not terminated yet when another thread thinks it already is.


git-svn-id: file:///home/lennart/svn/public/pulseaudio/trunk@1387 fefdeb5f-60dc-0310-8127-8f9354f1896f

src/pulsecore/once-posix.c

@@ -0,0 +1,69 @@
+/* $Id$ */
+
+/***
+  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.
+***/
+
+#ifdef HAVE_CONFIG_H
+#include <config.h>
+#endif
+
+#include <pthread.h>
+#include <assert.h>
+
+#include <pulsecore/mutex.h>
+
+#include "once.h"
+
+#define ASSERT_SUCCESS(x) do { \
+    int _r = (x); \
+    assert(_r == 0); \
+} while(0)
+
+static pa_mutex *global_mutex; 
+static pthread_once_t global_mutex_once = PTHREAD_ONCE_INIT;
+
+static void global_mutex_once_func(void) { 
+    global_mutex = pa_mutex_new(0); 
+} 
+
+void pa_once(pa_once_t *control, pa_once_func_t func) { 
+    assert(control); 
+    assert(func); 
+    
+    /* Create the global mutex */
+    ASSERT_SUCCESS(pthread_once(&global_mutex_once, global_mutex_once_func)); 
+
+    /* Create the local mutex */
+    pa_mutex_lock(global_mutex); 
+    if (!control->mutex)
+        control->mutex = pa_mutex_new(1);
+    pa_mutex_unlock(global_mutex);
+
+    /* Execute function */
+    pa_mutex_lock(control->mutex);
+    if (!control->once_value) {
+        control->once_value = 1;
+        func();
+    }
+    pa_mutex_unlock(control->mutex); 
+
+    /* 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. */
+} 

src/pulsecore/once.h

@@ -22,21 +22,17 @@
   USA.
 ***/
 
-#include <pulsecore/atomic.h>
+#include <pulsecore/mutex.h>
 
 typedef struct pa_once {
-    pa_atomic_int_t atomic;
+    unsigned int once_value;
+    pa_mutex *mutex;
 } pa_once_t;
 
-#define PA_ONCE_INIT { PA_ATOMIC_INIT(0) }
+#define PA_ONCE_INIT { .once_value = 0, .mutex = NULL }
-
-#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) {
+void pa_once(pa_once_t *o, pa_once_func_t f);
-    if (pa_once_test(o))
-        f();
-}
 
 #endif