Another problem with the thread but I think I did something wrong. In my plugin, I have one thread that send messages to Pd and processes the DSP chain. I have another thread that manages the GUI. From this thread, I also send messages to Pd but to avoid thread concurrency issues I use "sys_lock" and "sys_unlock". But this seems to produce artifacts (small cracks). When I remove the GUI, there is no more artifacts. And previously when I used a timer (attached to a specific thread) for each GUI object there were a lot of artifacts. So I think the thread context and the artifacts are linked but I can't figure out the real problem. My ideas are a bit going in circle for now so do you think there would be something that I forgot or something goes beyond my knowledge? Should I try to synchronize all the messages on the "main" DSP thread?

Cheers, Pierre