output/Multiple: move Wait() to struct PlayerControl

Eliminate a dependency from MultipleOutputs on PlayerControl.

src/player/Control.cxx

@@ -21,6 +21,7 @@
 #include "Control.hxx"
 #include "Idle.hxx"
 #include "DetachedSong.hxx"
+#include "output/MultipleOutputs.hxx"
 
 #include <algorithm>
 
@@ -46,6 +47,18 @@ PlayerControl::~PlayerControl()
 	delete tagged_song;
 }
 
+bool
+PlayerControl::WaitOutputConsumed(unsigned threshold)
+{
+	bool result = outputs.Check() < threshold;
+	if (!result && command == PlayerCommand::NONE) {
+		Wait();
+		result = outputs.Check() < threshold;
+	}
+
+	return result;
+}
+
 void
 PlayerControl::Play(DetachedSong *song)
 {

src/player/Control.hxx

@@ -280,6 +280,23 @@ struct PlayerControl {
 		CommandFinished();
 	}
 
+	/**
+	 * Checks if the size of the #MusicPipe is below the #threshold.  If
+	 * not, it attempts to synchronize with all output threads, and waits
+	 * until another #MusicChunk is finished.
+	 *
+	 * Caller must lock the mutex.
+	 *
+	 * @param threshold the maximum number of chunks in the pipe
+	 * @return true if there are less than #threshold chunks in the pipe
+	 */
+	bool WaitOutputConsumed(unsigned threshold);
+
+	bool LockWaitOutputConsumed(unsigned threshold) {
+		const ScopeLock protect(mutex);
+		return WaitOutputConsumed(threshold);
+	}
+
 private:
 	/**
 	 * Wait for the command to be finished by the player thread.

src/player/Thread.cxx

@@ -500,7 +500,7 @@ Player::CheckDecoderStartup()
 		pc.Unlock();
 
 		if (output_open &&
-		    !pc.outputs.Wait(pc, 1))
+		    !pc.LockWaitOutputConsumed(1))
 			/* the output devices havn't finished playing
 			   all chunks yet - wait for that */
 			return true;
@@ -813,7 +813,7 @@ play_chunk(PlayerControl &pc,
 inline bool
 Player::PlayNextChunk()
 {
-	if (!pc.outputs.Wait(pc, 64))
+	if (!pc.LockWaitOutputConsumed(64))
 		/* the output pipe is still large enough, don't send
 		   another chunk */
 		return true;