[sdljava-users] JNI pitfall

[Robert S. <the...@gm...>]

Hi list,
I was writing on a small demo app which at some place included these lines:

if (!measureFPS) {
            SDLMixer.openAudio(44100, SDLMixer.AUDIO_S16SYS, 2, 2048);

            System.out.println("Loading song.");

            MixMusic song = SDLMixer.loadMUS(Thread.currentThread()
                    .getContextClassLoader()
                    .getResourceAsStream("memesong.ogg"));

            System.out.println("Playing song: " + song);
            SDLMixer.playMusic(song, 0);
}

The code does not look very special but at runtime something odd will 
happen: You will hear a small bit of music and then it stops. The reason 
for this is that the MixMusic instance 'song' gets garbage collected 
when the if-block ends. I describe this here because this behavior is 
caused by the way Swig handles native pointers and can be a pitfall for 
others as it was for me.

You can work around this problem by assigning an instance like MixMusic 
(which in the above example is a local variable) to an instance or class 
variable.

@Ivan: If you are going to write a FAQ for SDLJava sometime it would be 
good to add this issue to it.

cu
Robert