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Postings from April 2007
Jan Dubois wrote: > On Tue, 17 Apr 2007, Steve Hay wrote: >> Picking a PID that you know exists is easy, but how do you pick a PID >> that you know doesn't exist? PID 0 currently doesn't exist on my >> (WinXP) system, and it probably never does, but I've no idea how >> portable that might be. > > PID 0 is used by the "System Idle Process". Doh! Yes, I see it in my Task manager now. I wonder why I didn't notice it before. Not enough coffee, obviously. > It is also used under POSIX > to indicate the current process group: > > http://www.opengroup.org/onlinepubs/009695399/functions/kill.html > > Note that with the current implementation of kill() and killpg() we can > only kill() processes that are running under the same uid as the perl > process itself. This limitation also applies to kill(0, $pid), so even > though pid 0 may exist, you don't see it because it is owned by the > system account. > > This limitation is true even when you are running with Administrator > rights. We can fix this by trying to acquire the SeDebugPrivilege > privilege for the current perl process. I just didn't want to have this > privilege turned on permanently. I'll try to come up with a patch that > just turns it on for the OpenProcess() call and then turns it off again. That would be useful. It would at least have saved me kidding myself that there wasn't a PID 0 when there is! > > As for finding a non-existing PID, I was thinking about just running it > over a huge list of integers (1..30_000) and see if *all* the processes > seem to exist, which seems rather unlikely. Anyways, that test would > have caught the specific failure I fixed with this patch. The attached works OK for me (and fails OK if I revert your fix). Is this all right now? --Thread Previous | Thread Next