MythPlayer: Fix a Live TV channel change deadlock.

This recognises that the decoder loop effectively has 3 different states
- running, partially paused and completely paused. The partial pause
state still allows the playback thread to decode a single frame on
demand, seek and perform position map syncs. Allowing these while the
decoder is changing adds various complications - hence add a new member
state variable, totalDecoderPause, that ensures the decoder loop does
nothing other than check its own pause state when completely paused.

Aside from fixing a deadlock on channel changes, this should also
speedup decoder changes under certain situations and probably prevents a
couple of even more obscure bugs (e.g. if a seek is triggered at the
same time as a channel change).

mythtv/libs/libmythtv/mythplayer.cpp

@@ -130,7 +130,8 @@ MythPlayer::MythPlayer(bool muted)
       parentWidget(NULL), embedid(0),
       embx(-1), emby(-1), embw(-1), embh(-1),
       // State
-      decoderPaused(false), pauseDecoder(false), unpauseDecoder(false),
+      totalDecoderPause(false), decoderPaused(false),
+      pauseDecoder(false), unpauseDecoder(false),
       killdecoder(false),   decoderSeek(-1),     decodeOneFrame(false),
       needNewPauseFrame(false),
       bufferPaused(false),  videoPaused(false),
@@ -2779,6 +2780,12 @@ void MythPlayer::DecoderLoop(bool pause)
     {
         DecoderPauseCheck();
 
+        if (totalDecoderPause)
+        {
+            usleep(1000);
+            continue;
+        }
+
         if (!decoder_change_lock.tryLock(1))
             continue;
         if (decoder)
@@ -4493,6 +4500,7 @@ bool MythPlayer::SetVideoByComponentTag(int tag)
  */
 void MythPlayer::SetDecoder(DecoderBase *dec)
 {
+    totalDecoderPause = true;
     PauseDecoder();
 
     {
@@ -4509,6 +4517,8 @@ void MythPlayer::SetDecoder(DecoderBase *dec)
         }
         decoder_change_lock.unlock();
     }
+
+    totalDecoderPause = false;
 }
 
 bool MythPlayer::PosMapFromEnc(unsigned long long start,

mythtv/libs/libmythtv/mythplayer.h

@@ -532,6 +532,7 @@ class MPUBLIC MythPlayer
     QWaitCondition decoderThreadUnpause;
     mutable QMutex decoderPauseLock;
     mutable QMutex decoderSeekLock;
+    bool           totalDecoderPause;
     bool           decoderPaused;
     bool           pauseDecoder;
     bool           unpauseDecoder;