On Sun, Sep 2, 2012 at 2:41 AM, Alan Gauld <alan.ga...@btinternet.com> wrote: > >> if __name__ == '__main__': # <-- required for Windows > > Why? > What difference does that make in Windows?
It's a hack to get around the fact that Win32 doesn't fork(). Windows calls CreateProcess(), which loads a fresh interpreter. multiprocessing then loads the module under a different name (i.e. not '__main__'). Otherwise another processing Pool would be created, etc, etc. This is also why you can't share global data in Windows. A forked process in Linux uses copy on write, so you can load a large block of data before calling fork() and share it. In Windows the module is executed separately for each process, so each has its own copy. To share data in Windows, I think the fastest option is to use a ctypes shared Array. The example I wrote is just using the default Pool setup that serializes (pickle) over pipes. FYI, the Win32 API imposes the requirement to use CreateProcess(). The native NT kernel has no problem forking (e.g. for the POSIX subsystem). I haven't looked closely enough to know why they didn't implement fork() in Win32. _______________________________________________ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
