Hi, I don't know if this issue is due to me, Racket, Xlib FFI or Xlib in itself, but I'm struggling with it. Hopefully someone knows. In a multi-threaded application using Jon's Xlib FFI ( <a href="https://github.com/kazzmir/x11-racket">https://github.com/kazzmir/x11-racket</a> ), I'm using one thread for processing X events with XNextEvent, which is a blocking call (apparently on a socket). I have another thread that listens to a tcp port, and does not need to do any X call. The problem is that the second thread blocks on 'read' even if there is something in the queue to read, unless some X event unblocks XNextEvent, in which case both threads run, until there is no X event left (and XNextEvent blocks again). I have called XInitThreads prior to any other X call to enable threads (and the return values says it's ok). Any idea anyone? Thanks, Laurent