• Paul Eggert's avatar
    Don't let call-process be a zombie factory. · bb5f74ee
    Paul Eggert authored
    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.
    
    Fixes: debbugs:12980
    bb5f74ee
process.h 7.19 KB