Steven D'Aprano wrote: > I have a problem and I don't know where to start looking for a solution. > > I have a class that needs to call an arbitrary function and wait for a > result. The function, being completely arbitrary and not under my control, > may be very time consuming and possibly may not even halt. My class needs > to be able to give up waiting for a result after a specified amount of > time. > > I'm thinking something conceptually like this: > > # pseudo-code: > set time out to 30 seconds > try: > result = somefunction() > except TimeOut: > # 30 second time out happened > print "somefunction() timed out without returning" > else: > print "somefunction() returned %s" % result > > > The easy (for some definition of easy) solution would be to code > somefunction() so that it raised an exception if it hadn't returned a > result within a certain time. Unfortunately, I can't do rely on that -- I > only have control over the calling code, not the called somefunction(), > which may be any arbitrary function. > > How do others handle something like this? What should I be looking for? > I'm after a lightweight solution, if any such thing exists.
For simple cases, I would use signal.alarm() with a SIGALARM handler that raises a TimeOut exception. However, this is by no means foolproof; you have to rely on the called function not to mess with your signal handler. Plus, if your alarm occurs within a try-except block that catches the TimeOut, it'll still be dropped. And to the best of my knowledge, you can't otherwise forcibly terminate the execution of a Python thread or block of code. If you're going to be running untrusted code, I would use the subprocess module to invoke a separate Python instance which takes the code to be executed on stdin, and returns a pickled copy of the return value on stdout. Then you can start it running, wait 30 seconds, and then kill it if it hasn't already returned. -- David -- http://mail.python.org/mailman/listinfo/python-list
