Why not have the parent call setsid() / setpgid() at the beginning? This should prevent the PID from getting recycled until every process in the process group exits.
Julian Hsiao mad...@nyanisore.net On Apr 2, 2010, at 8:10 PM, Michael Ash wrote: > On Thu, Apr 1, 2010 at 7:19 PM, Dave Keck <davek...@gmail.com> wrote: >>>> Look like a race condition. The man page says getppid() will not fail, but >>>> not what happens after the parent dies. I will test this. >>> >>> If the parent dies, the process becomes the child of launchd. For a quick >>> fix I checked for the parent PID greater than 1. >>> >>> A better fix, the parent process passed its PID to the child process as an >>> argument. In the child process, if getppid() does not return the PID from >>> the parent process, exit. >> >> Another problem is if the parent dies after the getppid(), and another >> process starts with the same PID as the old parent, all before the >> call to kevent(). In this scenario you'll now be waiting for an >> unrelated process to die. This situation is likely impossible >> currently with incrementing PIDs, but there's been mention of PID >> randomization on darwin-dev: >> >> http://lists.apple.com/archives/darwin-dev/2009/Oct/msg00056.html >> >> I only mention this because I use this kevent method to detect a >> parent's death, and have been looking for a better technique that >> also doesn't require the parent's cooperation... > > Call getppid, set up the kevent listener, then before you actually > block in kevent, call getppid *again*. If the answer matches the first > call, then you can go ahead and call kevent. If the answer doesn't > match, you've hit the race condition you outline here, your parent is > dead, and you can exit immediately. If the parent quits after the > second getppid but before the call to kevent, you should still get the > exit notification because you registered it before the parent quit. > > Mike _______________________________________________ Cocoa-dev mailing list (Cocoa-dev@lists.apple.com) Please do not post admin requests or moderator comments to the list. Contact the moderators at cocoa-dev-admins(at)lists.apple.com Help/Unsubscribe/Update your Subscription: http://lists.apple.com/mailman/options/cocoa-dev/archive%40mail-archive.com This email sent to arch...@mail-archive.com
