- apply the ZMusic mutex a bit more finely grained.

It should only guard the critical parts, like calling Stop() but can let Update and IsPlaying method work unhindered otherwise.

libraries/zmusic/musicformats/music_midi.cpp

@@ -570,10 +570,12 @@ bool MIDIStreamer::IsPlaying()
 {
 	if (m_Status != STATE_Stopped && (MIDI == NULL || (EndQueued != 0 && EndQueued < 4)))
 	{
+		std::lock_guard<std::mutex> lock(CritSec);
 		Stop();
 	}
 	if (m_Status != STATE_Stopped && !MIDI->IsOpen())
 	{
+		std::lock_guard<std::mutex> lock(CritSec);
 		Stop();
 	}
 	return m_Status != STATE_Stopped;
@@ -695,7 +697,11 @@ void MIDIStreamer::Callback(void *userdata)
 
 void MIDIStreamer::Update()
 {
-	if (MIDI != nullptr && !MIDI->Update()) Stop();
+	if (MIDI != nullptr && !MIDI->Update())
+	{
+		std::lock_guard<std::mutex> lock(CritSec);
+		Stop();
+	}
 }
 
 //==========================================================================

libraries/zmusic/zmusic/zmusic.cpp

@@ -340,28 +340,24 @@ void ZMusic_Start(MusInfo *song, int subsong, bool loop)
 void ZMusic_Pause(MusInfo *song)
 {
 	if (!song) return;
-	std::lock_guard<std::mutex> lock(song->CritSec);
 	song->Pause();
 }
 
 void ZMusic_Resume(MusInfo *song)
 {
 	if (!song) return;
-	std::lock_guard<std::mutex> lock(song->CritSec);
 	song->Resume();
 }
 
 void ZMusic_Update(MusInfo *song)
 {
 	if (!song) return;
-	std::lock_guard<std::mutex> lock(song->CritSec);
 	song->Update();
 }
 
 bool ZMusic_IsPlaying(MusInfo *song)
 {
 	if (!song) return false;
-	std::lock_guard<std::mutex> lock(song->CritSec);
 	return song->IsPlaying();
 }