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