I might have missed something obvious but there seems to be a race condition 
resulting in a deadlock in libpulse 0.9.22 (Debian).

I have stream with prebuf disabled (zero). When the Close() function below 
gets called, if the stream is not corked, the pa_stream_drain() callback 
never gets called, so pa_threaded_mainloop_wait() never returns and the whole 
process jams.

This seems timing dependent: if I put a gdb breakpoint on 
pa_operation_get_state() then continue, the callback does get called and the 
process does not get stuck on the condition variable. There is also no problem 
if the stream is corked, in which case we use pa_stream_flush() instead of 
pa_stream_drain().

The code follows:

static void stream_success_cb(pa_stream *s, int success, void *userdata)
{
    pa_threaded_mainloop *mainloop = userdata;

    fprintf(stderr, "DONE: %d\n", success);
    pa_threaded_mainloop_signal(mainloop, 0);
    (void) s;
    (void) success;
}

/* ... */

static void Close(vlc_object_t *obj)
{
    aout_instance_t *aout = (aout_instance_t *)obj;
    aout_sys_t *sys = aout->output.p_sys;
    pa_threaded_mainloop *mainloop = sys->mainloop;
    pa_context *ctx = sys->context;
    pa_stream *s = sys->stream;

    /* ... */

    pa_threaded_mainloop_lock(mainloop);
    if (s != NULL) {
        pa_operation *op;

        if (pa_stream_is_corked(s) > 0)
            /* Stream paused: discard all buffers */
            op = pa_stream_flush(s, stream_success_cb, mainloop);
        else
            /* Stream playing: wait until buffers are played */
            op = pa_stream_drain(s, stream_success_cb, mainloop);
        if (likely(op != NULL)) {
            while (pa_operation_get_state(op) == PA_OPERATION_RUNNING) {
                fprintf(stderr, "waiting\n");
                pa_threaded_mainloop_wait(mainloop);
            }
            pa_operation_unref(op);
        }

        pa_stream_disconnect(s);
        pa_stream_unref(s);
    }
    if (ctx != NULL)
        pa_context_unref(ctx);
    pa_threaded_mainloop_unlock(mainloop);
    pa_threaded_mainloop_free(mainloop);
    free(sys);
}