added a lock/unlock_lib pair to allow extern progs to serialize access to lavc.

Originally committed as revision 3899 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/beosthread.c

@@ -33,6 +33,25 @@ typedef struct ThreadContext{
     int ret;
 }ThreadContext;
 
+// it's odd Be never patented that :D
+struct benaphore {
+	vint32 atom;
+	sem_id sem;
+};
+static inline int lock_ben(struct benaphore *ben)
+{
+	if (atomic_add(&ben->atom, 1) > 0)
+		return acquire_sem(ben->sem);
+	return B_OK;
+}
+static inline int unlock_ben(struct benaphore *ben)
+{
+	if (atomic_add(&ben->atom, -1) > 1)
+		return release_sem(ben->sem);
+	return B_OK;
+}
+
+static struct benaphore av_thread_lib_ben;
 
 static int32 ff_thread_func(void *v){
     ThreadContext *c= v;
@@ -131,3 +150,31 @@ fail:
     avcodec_thread_free(s);
     return -1;
 }
+
+/* provide a mean to serialize calls to avcodec_*() for thread safety. */
+
+int avcodec_thread_lock_lib(void)
+{
+	return lock_ben(&av_thread_lib_ben);
+}
+
+int avcodec_thread_unlock_lib(void)
+{
+	return unlock_ben(&av_thread_lib_ben);
+}
+
+/* our versions of _init and _fini (which are called by those actually from crt.o) */
+
+void initialize_after(void)
+{
+	av_thread_lib_ben.atom = 0;
+	av_thread_lib_ben.sem = create_sem(0, "libavcodec benaphore");
+}
+
+void uninitialize_before(void)
+{
+	delete_sem(av_thread_lib_ben.sem);
+}
+
+
+