# Class Uq_engines.poll_process_engine

    class poll_process_engine : ?period:float -> pid:int -> Unixqueue.event_system -> [Unix.process_status] engine

This class is deprecated! Use the classes in `Shell_uq` instead.

This engine waits until the process with the ID `pid` terminates. When this happens, the state of the engine changes to ``Done`, and the argument of ``Done` is the process status.

The engine does not catch stopped processes.

The engine checks the process status every `period` seconds, and whenever there is a `Signal` event on the queue. The idea of the latter is that the user of this engine can increase the responsiveness by defining a signal handler for SIGCHLD signals (the handler need not to perform any special action, it must just be defined). When the sub process terminates, a SIGCHLD signal is sent to the current process. If the event loop happens to wait for new conditions (which is usually very likely), a `Signal` event will be generated, and the engine will check the process status very soon. Note that it is not guaranteed that a terminating process triggers a `Signal` event, although it is very likely.

You can define an empty SIGCHLD handler with:

     Sys.set_signal Sys.sigchld (Sys.Signal_handle (fun _ -> ()))

`period` : Every `period` seconds the process status is checked. Defaults to 0.1 seconds.