Question

I have some CAD software I’ve written. Each component being drawn has a set of vertex buffer objects. If the component gets deleted, I have to free the vertex buffer objects in the finalize method such as:

    if (gl != null) {
        Integer[] keys = vbos.keySet().toArray(new Integer[0]);
        for (int i = 0; i < keys.length; i++) {
            Integer tmp = keys[i];
            if (tmp != null) {
                if (gl.glIsBufferARB(tmp.intValue()));
                gl.glDeleteBuffersARB(1, new int[]{tmp.intValue()}, 0);
            }
        }
    }

however I sometimes get a SIGSEV and JVM crash. The hs_err log file points to gl.glIsBufferArb(tmp.intValue()).

I believe this means my gl object is no longer valid?

It should have been still valid I think. The program was still operating up until the crash. Is there a way to free a glbuffer without having stored a reference to the GL object?

Thank you!

Answer 1

The most obvious issue you’re going to run into here is that an OpenGL context can only be referenced in the thread it is active in. Generally speaking this will be your rendering thread, which means that the OpenGL context will not be available in the JVM’s finalizer thread. That, to me, seems the most likely cause of your errors. I would recommend that you keep a global list of invalidated VBOs, and have the finalize method add ids to that list. You can then process that list periodically from your rendering threads, making the OpenGL calls necessary to actually delete the VBOs.

You can find a quick rundown on OpenGL’s behavior in a multi-threaded environment here.