extmidi: Do not continuously retry if execvp fails

See: #478

src/music/extmidi.cpp

@@ -101,8 +101,10 @@ void MusicDriver_ExtMidi::StopSong()
 
 bool MusicDriver_ExtMidi::IsSongPlaying()
 {
-	if (this->pid != -1 && waitpid(this->pid, nullptr, WNOHANG) == this->pid) {
+	int status = 0;
+	if (this->pid != -1 && waitpid(this->pid, &status, WNOHANG) == this->pid) {
 		this->pid = -1;
+		if (WIFEXITED(status) && WEXITSTATUS(status) == 255) this->failed = true;
 	}
 	if (this->pid == -1 && this->song[0] != '\0') this->DoPlay();
 	return this->pid != -1;
@@ -115,6 +117,7 @@ void MusicDriver_ExtMidi::SetVolume(byte vol)
 
 void MusicDriver_ExtMidi::DoPlay()
 {
+	this->failed = false;
 	this->pid = fork();
 	switch (this->pid) {
 		case 0: {
@@ -123,7 +126,7 @@ void MusicDriver_ExtMidi::DoPlay()
 			if (d != -1 && dup2(d, 1) != -1 && dup2(d, 2) != -1) {
 				execvp(this->params[0], this->params);
 			}
-			_exit(1);
+			_exit(255);
 		}
 
 		case -1:

src/music/extmidi.h

@@ -17,6 +17,7 @@ private:
 	char **params;
 	char song[MAX_PATH];
 	pid_t pid;
+	bool failed = false;
 
 	void DoPlay();
 	void DoStop();
@@ -34,6 +35,8 @@ public:
 
 	void SetVolume(byte vol) override;
 	const char *GetName() const override { return "extmidi"; }
+
+	bool IsInFailedState() override { return this->failed; }
 };
 
 class FMusicDriver_ExtMidi : public DriverFactoryBase {

src/music/music_driver.hpp

@@ -40,6 +40,12 @@ public:
 	 */
 	virtual void SetVolume(byte vol) = 0;
 
+	/**
+	 * Is playback in a failed state?
+	 * @return True if playback is in a failed state.
+	 */
+	virtual bool IsInFailedState() { return false; }
+
 	/**
 	 * Get the currently active instance of the music driver.
 	 */

src/music_gui.cpp

@@ -262,7 +262,13 @@ void MusicSystem::CheckStatus()
 	}
 	if (this->active_playlist.empty()) return;
 	/* If we were supposed to be playing, but music has stopped, move to next song */
-	if (this->IsPlaying() && !MusicDriver::GetInstance()->IsSongPlaying()) this->Next();
+	if (this->IsPlaying() && !MusicDriver::GetInstance()->IsSongPlaying()) {
+		if (MusicDriver::GetInstance()->IsInFailedState()) {
+			this->Stop();
+		} else {
+			this->Next();
+		}
+	}
 }
 
 /** Is the player getting music right now? */