I thought that maybe sys_unlock should be called before sys_send_dacs, because thats the only place that pd waits under linux. didn't doublecheck though.
I tried that yesterday and it works well (i also posted a patch at the patch tracker), although i'm not sure that this is really safe - what about [; pd dsp 0( posted during that time? (ok, maybe that's pathological)
best greetings, Thomas