Don't let call-process be a zombie factory.

[bpt/emacs.git] / src / ChangeLog

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 2012-12-03  Paul Eggert  <eggert@cs.ucla.edu>
 
+       Don't let call-process be a zombie factory (Bug#12980).
+       Fixing this bug required some cleanup of the signal-handling code.
+       As a side effect, this change also fixes a longstanding rare race
+       condition whereby Emacs could mistakenly kill unrelated processes,
+       and it fixes a bug where a second C-g does not kill a recalcitrant
+       synchronous process in GNU/Linux and similar platforms.
+       The patch should also fix the last vestiges of Bug#9488,
+       a bug which has mostly been fixed on the trunk by other changes.
+       * callproc.c, process.h (synch_process_alive, synch_process_death)
+       (synch_process_termsig, sync_process_retcode):
+       Remove.  All uses removed, to simplify analysis and so that
+       less consing is done inside critical sections.
+       * callproc.c (call_process_exited): Remove.  All uses replaced
+       with !synch_process_pid.
+       * callproc.c (synch_process_pid, synch_process_fd): New static vars.
+       These take the role of what used to be in unwind-protect arg.
+       All uses changed.
+       (block_child_signal, unblock_child_signal):
+       New functions, to avoid races that could kill innocent-victim processes.
+       (call_process_kill, call_process_cleanup, Fcall_process): Use them.
+       (call_process_kill): Record killed processes as deleted, so that
+       zombies do not clutter up the system.  Do this inside a critical
+       section, to avoid a race that would allow the clutter.
+       (call_process_cleanup): Fix code so that the second C-g works again
+       on common platforms such as GNU/Linux.
+       (Fcall_process): Create the child process in a critical section,
+       to fix a race condition.  If creating an asynchronous process,
+       record it as deleted so that zombies do not clutter up the system.
+       Do unwind-protect for WINDOWSNT too, as that's simpler in the
+       light of these changes.  Omit unnecessary call to emacs_close
+       before failure, as the unwind-protect code does that.
+       * callproc.c (call_process_cleanup):
+       * w32proc.c (waitpid): Simplify now that synch_process_alive is gone.
+       * process.c (record_deleted_pid): New function, containing
+       code refactored out of Fdelete_process.
+       (Fdelete_process): Use it.
+       (process_status_retrieved): Remove.  All callers changed to use
+       child_status_change.
+       (record_child_status_change): Remove, folding its contents into ...
+       (handle_child_signal): ... this signal handler.  Now, this
+       function is purely a handler for SIGCHLD, and is not called after
+       a synchronous waitpid returns; the synchronous code is moved to
+       wait_for_termination.  There is no need to worry about reaping
+       more than one child now.
+       * sysdep.c (get_child_status, child_status_changed): New functions.
+       (wait_for_termination): Now takes int * status and bool
+       interruptible arguments, too.  Do not record child status change;
+       that's now the caller's responsibility.  All callers changed.
+       Reimplement in terms of get_child_status.
+       (wait_for_termination_1, interruptible_wait_for_termination):
+       Remove.  All callers changed to use wait_for_termination.
+       * syswait.h: Include <stdbool.h>, for bool.
+       (record_child_status_change, interruptible_wait_for_termination):
+       Remove decls.
+       (record_deleted_pid, child_status_changed): New decls.
+       (wait_for_termination): Adjust to API changes noted above.
+
        * bytecode.c, lisp.h (Qbytecode): Remove.
        No longer needed after 2012-11-20 interactive-p changes.