osxvideosink: add code to optionally run the cocoa main runloop in a separate thread

Add a little hack to run the cocoa main runloop from a separate thread _when_
the main runloop is not being run (which means that the app doesn't use cocoa).
Runloops are thread specific, so the hack boils down to getting the runloop for
the main thread and setting it as the runloop for our dedicated thread.

sys/osxvideo/osxvideosink.h

@@ -31,6 +31,7 @@
 
 #include <string.h>
 #include <math.h>
+#include <objc/runtime.h>
 #include <Cocoa/Cocoa.h>
 
 #include <QuickTime/QuickTime.h>
@@ -72,10 +73,14 @@ struct _GstOSXVideoSink {
   /* Our element stuff */
   GstVideoSink videosink;
   GstOSXWindow *osxwindow;
-  gboolean app_started;
   void *osxvideosinkobject;
   NSView *superview;
+#ifdef RUN_NS_APP_THREAD
+  GThread *ns_app_thread;
+#else
   guint cocoa_timeout;
+  gboolean app_started;
+#endif
   gboolean keep_par;
   gboolean embed;
 };
@@ -118,6 +123,9 @@ GType gst_osx_video_sink_get_type(void);
   GstOSXVideoSink *osxvideosink;
 }
 
+#ifdef RUN_NS_APP_THREAD
++ (BOOL) isMainThread;
+#endif
 -(id) initWithSink: (GstOSXVideoSink *) sink;
 -(void) createInternalWindow;
 -(void) resize;

sys/osxvideo/osxvideosink.m

@@ -47,6 +47,11 @@
 GST_DEBUG_CATEGORY (gst_debug_osx_video_sink);
 #define GST_CAT_DEFAULT gst_debug_osx_video_sink
 
+#ifdef RUN_NS_APP_THREAD
+extern  void _CFRunLoopSetCurrent(CFRunLoopRef rl);
+extern pthread_t _CFMainPThread;
+#endif
+
 static GstStaticPadTemplate gst_osx_video_sink_sink_template_factory =
 GST_STATIC_PAD_TEMPLATE ("sink",
     GST_PAD_SINK,
@@ -87,44 +92,100 @@ gst_osx_video_sink_call_from_main_thread(NSObject * object, SEL function,
 
 /* Poll for cocoa events */
 static void
-cocoa_poll_events (void) {
+run_ns_app_loop (void) {
   NSEvent *event;
   NSAutoreleasePool *pool =[[NSAutoreleasePool alloc] init];
+  NSDate *pollTime = nil;
+
+#ifdef RUN_NS_APP_THREAD
+  /* when running the loop in a thread we want to sleep as long as possible */
+  pollTime = [NSDate distantFuture];
+#else
+  pollTime = [NSDate distantPast];
+#endif
 
   do {
-      event =[NSApp nextEventMatchingMask: NSAnyEventMask untilDate:
-          [NSDate distantPast] inMode:
-          NSDefaultRunLoopMode dequeue:YES];
+      event = [NSApp nextEventMatchingMask:NSAnyEventMask untilDate:pollTime
+          inMode:NSDefaultRunLoopMode dequeue:YES];
       [NSApp sendEvent:event];
     }
   while (event != nil);
   [pool release];
 }
 
+#ifdef RUN_NS_APP_THREAD
+static gpointer
+ns_app_loop_thread (gpointer data)
+{
+  NSAutoreleasePool *pool;
+
+  /* set the main runloop as the runloop for the current thread. This has the
+   * effect that calling NSApp nextEventMatchingMask:untilDate:inMode:dequeue
+   * runs the main runloop.
+   */
+  _CFRunLoopSetCurrent(CFRunLoopGetMain());
+
+  /* this is needed to make IsMainThread checks in core foundation work from the
+   * current thread
+   */
+  _CFMainPThread = pthread_self();
+
+  pool = [[NSAutoreleasePool alloc] init];
+
+  [NSApplication sharedApplication];
+  [NSApp finishLaunching];
+
+  /* run the loop */
+  run_ns_app_loop ();
+
+  [pool release];
+
+  return NULL;
+}
+#endif
+
 static void
 gst_osx_video_sink_run_cocoa_loop (GstOSXVideoSink * osxvideosink )
 {
-  /* Cocoa applications require a main run loop running to dispatch UI
+  /* Cocoa applications require a main runloop running to dispatch UI
    * events and process deferred calls to the main thread through
    * perfermSelectorOnMainThread.
    * Since the sink needs to create it's own Cocoa window when no
    * external NSView is passed to the sink through the GstXOverlay API,
-   * we need to replace cocoa's main run loop with a poller.
-   * We are also assuming that when the main run loop is not running
-   * (nor native Cocoa, nor GTK, nor QT), there is at least glib's main
-   * loop running.
+   * we need to run the cocoa mainloop somehow.
    */
   if ([[NSRunLoop mainRunLoop] currentMode] == nil) {
+#ifdef RUN_NS_APP_THREAD
+  /* run the main runloop in a separate thread */
+
+  /* override [NSThread isMainThread] with our own implementation so that we can
+   * make it believe our dedicated thread is the main thread 
+   */
+  Method origIsMainThread = class_getClassMethod([NSThread class],
+      NSSelectorFromString(@"isMainThread"));
+  Method ourIsMainThread = class_getClassMethod([GstOSXVideoSinkObject class],
+      NSSelectorFromString(@"isMainThread"));
+
+  method_exchangeImplementations(origIsMainThread, ourIsMainThread);
+
+  osxvideosink->ns_app_thread = g_thread_new ("GstNSAppThread",
+      ns_app_loop_thread, NULL);
+#else
+  /* assume that there is a GMainLoop and iterate the main runloop from there
+   */
   osxvideosink->cocoa_timeout = g_timeout_add (10,
-        (GSourceFunc) cocoa_poll_events, NULL);
+      (GSourceFunc) run_ns_app_loop, NULL);
+#endif
   }
 }
 
 static void
 gst_osx_video_sink_stop_cocoa_loop (GstOSXVideoSink * osxvideosink)
 {
+#ifndef RUN_NS_APP_THREAD
   if (osxvideosink->cocoa_timeout)
     g_source_remove(osxvideosink->cocoa_timeout);
+#endif
 }
 
 /* This function handles osx window creation */
@@ -416,7 +477,9 @@ gst_osx_video_sink_init (GstOSXVideoSink * osxvideosink)
   osxvideosink->superview = NULL;
   osxvideosink->osxvideosinkobject = [[GstOSXVideoSinkObject alloc]
     initWithSink:osxvideosink];
+#ifndef RUN_NS_APP_THREAD
   osxvideosink->app_started = FALSE;
+#endif
   osxvideosink->keep_par = FALSE;
 }
 
@@ -716,11 +779,13 @@ gst_osx_video_sink_get_type (void)
   rect.size.width = (float) osxwindow->width;
   rect.size.height = (float) osxwindow->height;
 
+#ifndef RUN_NS_APP_THREAD
   if (!osxvideosink->app_started) {
     [NSApplication sharedApplication];
     [NSApp finishLaunching];
     osxvideosink->app_started = TRUE;
   }
+#endif
 
   if (!GetCurrentProcess(&psn)) {
       TransformProcessType(&psn, kProcessTransformToForegroundApplication);
@@ -741,6 +806,14 @@ gst_osx_video_sink_get_type (void)
 
 }
 
+#ifdef RUN_NS_APP_THREAD
++ (BOOL) isMainThread
+{
+  /* FIXME: ideally we should return YES only for ->ns_app_thread here */
+  return YES;
+}
+#endif
+
 - (void) resize
 {
   GstOSXWindow *osxwindow = osxvideosink->osxwindow;