Fix a race condition with glib (Bug#8855).

This is a backport from the trunk, consisting of:

2012-11-17  Eli Zaretskii  <eliz@gnu.org>

* nt/inc/sys/wait.h: New file, with prototype of waitpid and
definitions of macros it needs.
* nt/inc/ms-w32.h (wait): Don't define, 'wait' is not used anymore.
(sys_wait): Remove prototype.
* nt/config.nt (HAVE_SYS_WAIT_H): Define to 1.
* src/w32proc.c (create_child): Don't clip the PID of the child
process to fit into an Emacs integer, as this is no longer a
restriction.
(waitpid): Rename from sys_wait.  Emulate a Posix 'waitpid' by
reaping only the process specified by PID argument, if that is
positive.  Use PID instead of dead_child to know which process to
reap.  Wait for the child to die only if WNOHANG is not in
OPTIONS.
(sys_select): Don't set dead_child.
* src/sysdep.c (wait_for_termination_1): Remove the WINDOWSNT portion,
as it is no longer needed.
* src/process.c (waitpid, WUNTRACED) [!WNOHANG]: Remove definitions,
no longer needed.
(record_child_status_change): Remove the setting of
record_at_most_one_child for the !WNOHANG case.

2012-11-03  Paul Eggert  <eggert@cs.ucla.edu>

Fix a race condition that causes Emacs to mess up glib (Bug#8855).
This is a backport from the trunk.
The symptom is a diagnostic "GLib-WARNING **: In call to
g_spawn_sync(), exit status of a child process was requested but
SIGCHLD action was set to SIG_IGN and ECHILD was received by
waitpid(), so exit status can't be returned."  The diagnostic
is partly wrong, as the SIGCHLD action is not set to SIG_IGN.
The real bug is a race condition between Emacs and glib: Emacs
does a waitpid (-1, ...) and reaps glib's subprocess by mistake,
so that glib can't find it.  Work around the bug by invoking
waitpid only on subprocesses that Emacs itself creates.
* src/process.c (create_process, record_child_status_change):
Don't use special value -1 in pid field, as the caller now must
know the pid rather than having the callee infer it.  The
inference was sometimes incorrect anyway, due to another race.
(create_process): Set new 'alive' member if child is created.
(process_status_retrieved): New function.
(record_child_status_change): Use it.
Accept negative 1st argument, which means to wait for the
processes that Emacs already knows about.  Move special-case code
for DOS_NT (which lacks WNOHANG) here, from caller.  Keep track of
processes that have already been waited for, by testing and
clearing new 'alive' member.
(CAN_HANDLE_MULTIPLE_CHILDREN): Remove, as record_child_status_change
now does this internally.
(handle_child_signal): Let record_child_status_change do all
the work, since we do not want to reap all exited child processes,
only the child processes that Emacs itself created.
* src/process.h (Lisp_Process): New boolean member 'alive'.

1 files changed, 57 insertions, 0 deletions

diff --git a/src/ChangeLog b/src/ChangeLog
index 88fbf7a99f2..655eb1595c0 100644
--- a/src/ChangeLog
+++ b/src/ChangeLog
@@ -1,3 +1,60 @@
+2012-11-23  Paul Eggert  <eggert@cs.ucla.edu>
+
+        Fix a race condition with glib (Bug#8855).
+        This is a backport from the trunk, consisting of:
+
+        2012-11-17  Eli Zaretskii  <eliz@gnu.org>
+
+        * w32proc.c (create_child): Don't clip the PID of the child
+        process to fit into an Emacs integer, as this is no longer a
+        restriction.
+        (waitpid): Rename from sys_wait.  Emulate a Posix 'waitpid' by
+        reaping only the process specified by PID argument, if that is
+        positive.  Use PID instead of dead_child to know which process to
+        reap.  Wait for the child to die only if WNOHANG is not in
+        OPTIONS.
+        (sys_select): Don't set dead_child.
+
+        * sysdep.c (wait_for_termination_1): Remove the WINDOWSNT portion,
+        as it is no longer needed.
+
+        * process.c (waitpid, WUNTRACED) [!WNOHANG]: Remove definitions,
+        no longer needed.
+        (record_child_status_change): Remove the setting of
+        record_at_most_one_child for the !WNOHANG case.
+
+        2012-11-03  Paul Eggert  <eggert@cs.ucla.edu>
+
+        Fix a race condition that causes Emacs to mess up glib (Bug#8855).
+        This is a backport from the trunk.
+        The symptom is a diagnostic "GLib-WARNING **: In call to
+        g_spawn_sync(), exit status of a child process was requested but
+        SIGCHLD action was set to SIG_IGN and ECHILD was received by
+        waitpid(), so exit status can't be returned."  The diagnostic
+        is partly wrong, as the SIGCHLD action is not set to SIG_IGN.
+        The real bug is a race condition between Emacs and glib: Emacs
+        does a waitpid (-1, ...) and reaps glib's subprocess by mistake,
+        so that glib can't find it.  Work around the bug by invoking
+        waitpid only on subprocesses that Emacs itself creates.
+        * process.c (create_process, record_child_status_change):
+        Don't use special value -1 in pid field, as the caller now must
+        know the pid rather than having the callee infer it.  The
+        inference was sometimes incorrect anyway, due to another race.
+        (create_process): Set new 'alive' member if child is created.
+        (process_status_retrieved): New function.
+        (record_child_status_change): Use it.
+        Accept negative 1st argument, which means to wait for the
+        processes that Emacs already knows about.  Move special-case code
+        for DOS_NT (which lacks WNOHANG) here, from caller.  Keep track of
+        processes that have already been waited for, by testing and
+        clearing new 'alive' member.
+        (CAN_HANDLE_MULTIPLE_CHILDREN): Remove, as record_child_status_change
+        now does this internally.
+        (handle_child_signal): Let record_child_status_change do all
+        the work, since we do not want to reap all exited child processes,
+        only the child processes that Emacs itself created.
+        * process.h (Lisp_Process): New boolean member 'alive'.
+
 2012-11-23  Eli Zaretskii  <eliz@gnu.org>
 
         * xdisp.c (set_cursor_from_row): Skip step 2 only if point is not