Hi all, This is a followup to a report back in 2011 about essentially the same issue:
https://cygwin.com/ml/cygwin/2011-04/msg00031.html The same test program in that report demonstrates the issue, but with kill sending any non-zero signal. To reiterate, the problem here is POSIX compliance with respect to sending signals to zombie processes: > Existing implementations vary on the result of a kill() with pid indicating > an inactive process (a > terminated process that has not been waited for by its parent). Some indicate > success on such a > call (subject to permission checking), while others give an error of [ESRCH]. > Since the definition > of process lifetime in this volume of POSIX.1-2008 covers inactive processes, > the [ESRCH] error > as described is inappropriate in this case. In particular, this means that an > application cannot > have a parent process check for termination of a particular child with > kill(). (Usually this is done > with the null signal; this can be done reliably with waitpid().) In response to the originally issue, this was fixed *specifically* for the case of kill(pid, 0). But my reading of the above is that kill() should return 0 in this case regardless of the signal (modulo permissions, etc.). On Linux, for example, when calling kill with pid of a zombie process the kernel will happily deliver the signal to the relevant task_struct; it will just never be acted on since the task will never run again. The below (untested) patch demonstrates the change I'm suggesting, though I don't know what other code, if any, might be involved in this. Please CC me on any replies since I'm not subscribed to the list. Thanks, Erik diff --git a/winsup/cygwin/signal.cc b/winsup/cygwin/signal.cc index ff101e3..d819e77 100644 --- a/winsup/cygwin/signal.cc +++ b/winsup/cygwin/signal.cc @@ -260,7 +260,7 @@ _pinfo::kill (siginfo_t& si) } this_pid = pid; } - else if (si.si_signo == 0 && this && process_state == PID_EXITED) + else if (this && process_state == PID_EXITED) { this_process_state = process_state; this_pid = pid; -- Problem reports: http://cygwin.com/problems.html FAQ: http://cygwin.com/faq/ Documentation: http://cygwin.com/docs.html Unsubscribe info: http://cygwin.com/ml/#unsubscribe-simple
