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'.

4 files changed, 47 insertions, 4 deletions

diff --git a/nt/ChangeLog b/nt/ChangeLog
index f11f1fc5fc5..b4537de0d4f 100644
--- a/nt/ChangeLog
+++ b/nt/ChangeLog
@@ -1,3 +1,16 @@
+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>
+
+	* inc/sys/wait.h: New file, with prototype of waitpid and
+	definitions of macros it needs.
+	* inc/ms-w32.h (wait): Don't define, 'wait' is not used anymore.
+	(sys_wait): Remove prototype.
+	* config.nt (HAVE_SYS_WAIT_H): Define to 1.
+
 2012-11-20  Eli Zaretskii  <eliz@gnu.org>
 
 	* nmake.defs: Use !if, not !ifdef.  See
diff --git a/nt/config.nt b/nt/config.nt
index ed1cddf1e12..7e82283b41a 100644
--- a/nt/config.nt
+++ b/nt/config.nt
@@ -963,7 +963,7 @@ along with GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.  */
 #undef HAVE_SYS_VLIMIT_H
 
 /* Define to 1 if you have <sys/wait.h> that is POSIX.1 compatible. */
-#undef HAVE_SYS_WAIT_H
+#define HAVE_SYS_WAIT_H 1
 
 /* Define to 1 if you have the <term.h> header file. */
 #undef HAVE_TERM_H
diff --git a/nt/inc/ms-w32.h b/nt/inc/ms-w32.h
index dd2ae781cb8..a9a3049f9b0 100644
--- a/nt/inc/ms-w32.h
+++ b/nt/inc/ms-w32.h
@@ -185,15 +185,12 @@ extern char *getenv ();
 
 /* Subprocess calls that are emulated.  */
 #define spawnve sys_spawnve
-#define wait    sys_wait
 #define kill    sys_kill
 #define signal  sys_signal
 
 /* Internal signals.  */
 #define emacs_raise(sig) emacs_abort()
 
-extern int sys_wait (int *);
-
 /* termcap.c calls that are emulated.  */
 #define tputs   sys_tputs
 #define tgetstr sys_tgetstr
diff --git a/nt/inc/sys/wait.h b/nt/inc/sys/wait.h
new file mode 100644
index 00000000000..8d890c9e175
--- /dev/null
+++ b/nt/inc/sys/wait.h
@@ -0,0 +1,33 @@
+/* A limited emulation of sys/wait.h on Posix systems.
+
+Copyright (C) 2012  Free Software Foundation, Inc.
+
+This file is part of GNU Emacs.
+
+GNU Emacs is free software: you can redistribute it and/or modify
+it under the terms of the GNU General Public License as published by
+the Free Software Foundation, either version 3 of the License, or
+(at your option) any later version.
+
+GNU Emacs is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+GNU General Public License for more details.
+
+You should have received a copy of the GNU General Public License
+along with GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.  */
+
+#ifndef INC_SYS_WAIT_H_
+#define INC_SYS_WAIT_H_
+
+#define WNOHANG    1
+#define WUNTRACED  2
+#define WSTOPPED   2	/* same as WUNTRACED */
+#define WEXITED    4
+#define WCONTINUED 8
+
+/* The various WIF* macros are defined in src/syswait.h.  */
+
+extern pid_t waitpid (pid_t, int *, int);
+
+#endif	/* INC_SYS_WAIT_H_ */