On 16/03/2007 1.06, Greg Ewing wrote: >> Can you suggest any use-cases for thread termination which will *not* >> result in a completely broken and unpredictable heap after the thread >> has died? > > Suppose you have a GUI and you want to launch a > long-running computation without blocking the > user interface. You don't know how long it will > take, so you want the user to be able to cancel > it if he gets bored. > > There's no single place in the code where you > could put in a check for cancellation. Sprinkling > such checks all over the place would be tedious, > or even impossible if large amounts of time are > spent in calls to a third-party library that > wasn't designed for such things. > > Interaction with the rest of the program is > extremely limited -- some data is passed in, > it churns away, and some data is returned. It > doesn't matter what happens to its internal > state if it gets interrupted, as it's all going > to be thrown away. > > In that situation, it doesn't seem unreasonable > to me to want to be able to just kill the thread. > I don't see how it could do any more harm than > using KeyboardInterrupt to kill a program, > because that's all it is -- a subprogram running > inside your main program. > > How would you handle this situation?
It's really simple: don't use threads, use processes! Spawn an external process which does the calculation, pass data to it through pipe/socket/namedpipe/xmlrpc/whatever and read data back from it when it's done. If you need to kill it, just kill it away, at any asynchronous time: the OS will clean up after it. After many years working with these issues, I came to the personal conclusion of avoiding threads as much as possible. Threads are processes with shared memory, but in many real-world use cases I faced, there is really only a very little chunk of memory which is shared, and Python makes it incredibly easy to marshal data to a process (pickle or whatever). So in many cases there's really little excuses for going mad with threads. -- Giovanni Bajo _______________________________________________ Python-Dev mailing list Python-Dev@python.org http://mail.python.org/mailman/listinfo/python-dev Unsubscribe: http://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
