getLengthFromFile() : fix pthread conditions

don't use static variables when we can avoid
it might be true that we only have one Media instance in the program but we never know
also we must check for the condition because of spurious wakeups

vlc-android/jni/libvlcjni.c

@@ -416,52 +416,66 @@ jboolean Java_org_videolan_vlc_android_LibVLC_hasVideoTrack(JNIEnv *env, jobject
     return 0;
 }
 
-static pthread_mutex_t doneMutex;
-static pthread_cond_t doneCondVar;
+struct length_change_monitor {
+    pthread_mutex_t doneMutex;
+    pthread_cond_t doneCondVar;
+    bool length_changed;
+};
 
 static void length_changed_callback(const libvlc_event_t *ev, void *data)
 {
-    pthread_mutex_lock(&doneMutex);
-    pthread_cond_signal(&doneCondVar);
-    pthread_mutex_unlock(&doneMutex);
+    struct length_change_monitor *monitor = data;
+    pthread_mutex_lock(&monitor->doneMutex);
+    monitor->length_changed = true;
+    pthread_cond_signal(&monitor->doneCondVar);
+    pthread_mutex_unlock(&monitor->doneMutex);
 }
 
 jlong Java_org_videolan_vlc_android_LibVLC_getLengthFromFile(JNIEnv *env, jobject thiz,
                                                         jint i_instance, jstring filePath)
 {
-    libvlc_media_t *m;
-    libvlc_media_player_t *mp;
+    jlong length = 0;
+    struct length_change_monitor *monitor;
+    monitor = malloc(sizeof(*monitor));
+    if (!monitor)
+        return 0;
 
     /* Initialize pthread variables. */
-    pthread_mutex_init(&doneMutex, NULL);
-    pthread_cond_init(&doneCondVar, NULL);
+    pthread_mutex_init(&monitor->doneMutex, NULL);
+    pthread_cond_init(&monitor->doneCondVar, NULL);
+    monitor->length_changed = false;
 
     libvlc_instance_t *p_instance = (libvlc_instance_t *)i_instance;
     const char *psz_filePath = (*env)->GetStringUTFChars(env, filePath, 0);
 
     /* Create a new item and assign it to the media player. */
-    m = libvlc_media_new_path(p_instance, psz_filePath);
+    libvlc_media_t *m = libvlc_media_new_path(p_instance, psz_filePath);
     if (m == NULL)
     {
         LOGE("Couldn't create the media to play!");
-        return 0;
+        goto end;
     }
 
     /* Create a media player playing environment */
-    mp = libvlc_media_player_new_from_media (m);
+    libvlc_media_player_t *mp = libvlc_media_player_new_from_media (m);
     libvlc_event_manager_t *ev = libvlc_media_player_event_manager(mp);
-    libvlc_event_attach(ev, libvlc_MediaPlayerLengthChanged, length_changed_callback, NULL);
+    libvlc_event_attach(ev, libvlc_MediaPlayerLengthChanged, length_changed_callback, monitor);
     libvlc_media_release (m);
     libvlc_media_player_play( mp );
-    pthread_mutex_lock(&doneMutex);
-    pthread_cond_wait(&doneCondVar, &doneMutex);
-    pthread_mutex_unlock(&doneMutex);
-    jlong length = (jlong)libvlc_media_player_get_length( mp );
+
+    pthread_mutex_lock(&monitor->doneMutex);
+    while (!monitor->length_changed)
+        pthread_cond_wait(&monitor->doneCondVar, &monitor->doneMutex);
+    pthread_mutex_unlock(&monitor->doneMutex);
+
+    length = libvlc_media_player_get_length( mp );
     libvlc_media_player_stop( mp );
     libvlc_media_player_release( mp );
 
-    pthread_mutex_destroy(&doneMutex);
-    pthread_cond_destroy(&doneCondVar);
+end:
+    pthread_mutex_destroy(&monitor->doneMutex);
+    pthread_cond_destroy(&monitor->doneCondVar);
+    free(monitor);
 
     return length;
 }