On Wed, Apr 05, 2006 at 06:03:31AM -0400, [EMAIL PROTECTED] wrote: > It's no different from a file descriptor on UNIX. > > Neither UNIX nor Windows promise that a process identifier is valid > beyond the life of the process. UNIX avoids it from happening, as it > is necessary to avoid races with system calls such as kill(). Windows > does not have this problem.
But consider, why is the process id there? (Amongst other reasons) so that users can monitor pg_stat_activity and kill a backend that's out of control. The equivalent to this in windows would be to. 1. Get HANDLE from the process ID. 2. TerminateProcess with that HANDLE. Presumably users have a little GUI app that displays processes on the system with the process ID so they can kill it. If a process ID is quickly reused, they may end up killing the wrong one. The race condition in this case involves the user and you can't solve that programmatically. The non-reuse of pids is more for user-friendlyness than anything else. The Window use of HANDLE doesn't solve this problem at all. > Sure. Serial. Allocate on process start. > > Or, back to another topic from months ago - UUID generation... :-) Neither of which solve the "I'm a user and want to kill *that* backend" problem. Because even on windows you'll have to get the process id, convert it to a handle an kill it. Same race condition. > Process identifier should not be used beyond the life of the process. > As soon as wait() removes the process on UNIX, the process identifier > is no longer valid, and could be reused. That the operating system tries > to prevent problems by avoiding recycling isn't necessarily a good > reason to exploit this capability. Yeah, but it's very useful as a user. Consider this scenerio: <process 1234 goes AWOL> kill -INT 1234 <check if process still there> kill -TERM 1234 <process still there, damn it!> kill -9 1234 There gone. With no quick PID reuse I can be sure I won't kill the wrong one. This is presumably why recent versions of windows don't reuse pids quickly either... It for *users* not programs. -- Martijn van Oosterhout <kleptog@svana.org> http://svana.org/kleptog/ > Patent. n. Genius is 5% inspiration and 95% perspiration. A patent is a > tool for doing 5% of the work and then sitting around waiting for someone > else to do the other 95% so you can sue them.
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