Playback: Start playback and seek in the background

Perform playback start and seeking operations in the background, instead
of on the main thread, which should help prevent them from stalling the
user interface.

Signed-off-by: Christopher Snowhill <kode54@gmail.com>

Application/PlaybackController.m

@@ -23,6 +23,35 @@
 
 extern BOOL kAppControllerShuttingDown;
 
+@implementation NSObject (NxAdditions)
+
+-(void)performSelectorInBackground:(SEL)selector withObjects:(id)object, ...
+{
+	NSMethodSignature *signature = [self methodSignatureForSelector:selector];
+
+	// Setup the invocation
+	NSInvocation *invocation = [NSInvocation invocationWithMethodSignature:signature];
+	invocation.target = self;
+	invocation.selector = selector;
+
+	// Associate the arguments
+	va_list objects;
+	va_start(objects, object);
+	unsigned int objectCounter = 2;
+	for (id obj = object; obj != nil; obj = va_arg(objects, id))
+	{
+		[invocation setArgument:&obj atIndex:objectCounter++];
+	}
+	va_end(objects);
+
+	// Make sure to invoke on a background queue
+	NSInvocationOperation *operation = [[NSInvocationOperation alloc] initWithInvocation:invocation];
+	NSOperationQueue *backgroundQueue = [[NSOperationQueue alloc] init];
+	[backgroundQueue addOperation:operation];
+}
+
+@end
+
 @implementation PlaybackController
 
 #define DEFAULT_SEEK 5
@@ -241,7 +270,7 @@ - (void)playEntry:(PlaylistEntry *)pe startPaused:(BOOL)paused andSeekTo:(id)off
 
 	double seekTime = pe.seekable ? [offset doubleValue] : 0.0;
 
-	[audioPlayer play:pe.url withUserInfo:pe withRGInfo:makeRGInfo(pe) startPaused:paused andSeekTo:seekTime];
+	[audioPlayer performSelectorInBackground:@selector(playBG:withUserInfo:withRGInfo:startPaused:andSeekTo:) withObjects:pe.url, pe, makeRGInfo(pe), @(paused), @(seekTime), nil];
 }
 
 - (IBAction)next:(id)sender {
@@ -272,7 +301,7 @@ - (void)updatePosition:(id)sender {
 - (IBAction)seek:(id)sender {
 	double time = [sender doubleValue];
 
-	[audioPlayer seekToTime:time];
+	[audioPlayer performSelectorInBackground:@selector(seekToTimeBG:) withObject:@(time)];
 
 	lastPosition = -10;
 
@@ -289,7 +318,7 @@ - (IBAction)seek:(id)sender toTime:(NSTimeInterval)position {
 
 	lastPosition = -10;
 
-	[audioPlayer seekToTime:time];
+	[audioPlayer performSelectorInBackground:@selector(seekToTimeBG:) withObject:@(time)];
 
 	[self setPosition:time];
 
@@ -321,7 +350,7 @@ - (void)seekForward:(double)amount {
 		[self next:self];
 	} else {
 		lastPosition = -10;
-		[audioPlayer seekToTime:seekTo];
+		[audioPlayer performSelectorInBackground:@selector(seekToTimeBG:) withObject:@(seekTo)];
 		[self setPosition:seekTo];
 	}
 }
@@ -338,7 +367,7 @@ - (void)seekBackward:(double)amount {
 
 	lastPosition = -10;
 
-	[audioPlayer seekToTime:seekTo];
+	[audioPlayer performSelectorInBackground:@selector(seekToTimeBG:) withObject:@(seekTo)];
 	[self setPosition:seekTo];
 }
 
@@ -704,7 +733,7 @@ - (void)audioPlayer:(AudioPlayer *)player restartPlaybackAtCurrentPosition:(id)u
 	PlaylistEntry *pe = [playlistController currentEntry];
 	BOOL paused = playbackStatus == CogStatusPaused;
 	[[FIRCrashlytics crashlytics] logWithFormat:@"Restarting playback of track: %@", pe.url];
-	[player play:pe.url withUserInfo:pe withRGInfo:makeRGInfo(pe) startPaused:paused andSeekTo:pe.seekable ? pe.currentPosition : 0.0];
+	[player performSelectorInBackground:@selector(playBG:withUserInfo:withRGInfo:startPaused:andSeekTo:) withObjects:pe.url, pe, makeRGInfo(pe), @(paused), @(pe.seekable ? pe.currentPosition : 0.0), nil];
 }
 
 - (void)audioPlayer:(AudioPlayer *)player pushInfo:(NSDictionary *)info toTrack:(id)userInfo {

Audio/AudioPlayer.h

@@ -61,12 +61,14 @@
 - (void)play:(NSURL *)url withUserInfo:(id)userInfo withRGInfo:(NSDictionary *)rgi;
 - (void)play:(NSURL *)url withUserInfo:(id)userInfo withRGInfo:(NSDictionary *)rgi startPaused:(BOOL)paused;
 - (void)play:(NSURL *)url withUserInfo:(id)userInfo withRGInfo:(NSDictionary *)rgi startPaused:(BOOL)paused andSeekTo:(double)time;
+- (void)playBG:(NSURL *)url withUserInfo:(id)userInfo withRGInfo:(NSDictionary *)rgi startPaused:(NSNumber *)paused andSeekTo:(NSNumber *)time;
 
 - (void)stop;
 - (void)pause;
 - (void)resume;
 
 - (void)seekToTime:(double)time;
+- (void)seekToTimeBG:(NSNumber *)time;
 - (void)setVolume:(double)v;
 - (double)volume;
 - (double)volumeUp:(double)amount;

Audio/AudioPlayer.m

@@ -56,6 +56,10 @@ - (void)play:(NSURL *)url withUserInfo:(id)userInfo withRGInfo:(NSDictionary *)r
 	[self play:url withUserInfo:userInfo withRGInfo:rgi startPaused:paused andSeekTo:0.0];
 }
 
+- (void)playBG:(NSURL *)url withUserInfo:(id)userInfo withRGInfo:(NSDictionary *)rgi startPaused:(NSNumber *)paused andSeekTo:(NSNumber *)time {
+	[self play:url withUserInfo:userInfo withRGInfo:rgi startPaused:[paused boolValue] andSeekTo:[time doubleValue]];
+}
+
 - (void)play:(NSURL *)url withUserInfo:(id)userInfo withRGInfo:(NSDictionary *)rgi startPaused:(BOOL)paused andSeekTo:(double)time {
 	ALog(@"Opening file for playback: %@ at seek offset %f%@", url, time, (paused) ? @", starting paused" : @"");
 
@@ -165,6 +169,10 @@ - (void)resume {
 	[self setPlaybackStatus:CogStatusPlaying waitUntilDone:YES];
 }
 
+- (void)seekToTimeBG:(NSNumber *)time {
+	[self seekToTime:[time doubleValue]];
+}
+
 - (void)seekToTime:(double)time {
 	if(endOfInputReached) {
 		// This is a dirty hack in case the playback has finished with the track