Func. wait() should wait until all work is completed, but should not exit when block is locked()/unlocked() for flow-graph reconfiguration. It is unprobable, but during unlock() thread context might be switched after stop() is called but before new thread are executed by scheduller. This can cause exit from wait() when it is called (eg. from Python wrapper). Call of stop() is moved into lock(), no new work should be started on locked block and this gives threads some time to finish before join() is called from unlock().