+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
#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
/* 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
--- /dev/null
+/* 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_ */
+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
EMACS_TIME *, void *);
#endif
-#ifndef WNOHANG
-# undef waitpid
-# define waitpid(pid, status, options) wait (status)
-#endif
-#ifndef WUNTRACED
-# define WUNTRACED 0
-#endif
-
/* Work around GCC 4.7.0 bug with strict overflow checking; see
<http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52904>.
These lines can be removed once the GCC bug is fixed. */
#ifdef SIGCHLD
/* Fdelete_process promises to immediately forget about the process, but in
reality, Emacs needs to remember those processes until they have been
- treated by the SIGCHLD handler; otherwise this handler would consider the
- process as being synchronous and say that the synchronous process is
- dead. */
+ treated by the SIGCHLD handler and waitpid has been invoked on them;
+ otherwise they might fill up the kernel's process table. */
static Lisp_Object deleted_pid_list;
#endif
if (inchannel > max_process_desc)
max_process_desc = inchannel;
- /* Until we store the proper pid, enable the SIGCHLD handler
- to recognize an unknown pid as standing for this process.
- It is very important not to let this `marker' value stay
- in the table after this function has returned; if it does
- it might cause call-process to hang and subsequent asynchronous
- processes to get their return values scrambled. */
- XPROCESS (process)->pid = -1;
-
- /* This must be called after the above line because it may signal an
- error. */
+ /* This may signal an error. */
setup_process_coding_systems (process);
encoded_current_dir = ENCODE_FILE (current_dir);
#endif
XPROCESS (process)->pid = pid;
+ if (0 <= pid)
+ XPROCESS (process)->alive = 1;
/* Stop blocking signals in the parent. */
#ifdef SIGCHLD
return process;
}
\f
-/* On receipt of a signal that a child status has changed, loop asking
- about children with changed statuses until the system says there
- are no more.
+/* If the status of the process DESIRED has changed, return true and
+ set *STATUS to its exit status; otherwise, return false.
+ If HAVE is nonnegative, assume that HAVE = waitpid (HAVE, STATUS, ...)
+ has already been invoked, and do not invoke waitpid again. */
+
+static bool
+process_status_retrieved (pid_t desired, pid_t have, int *status)
+{
+ if (have < 0)
+ {
+ /* Invoke waitpid only with a known process ID; do not invoke
+ waitpid with a nonpositive argument. Otherwise, Emacs might
+ reap an unwanted process by mistake. For example, invoking
+ waitpid (-1, ...) can mess up glib by reaping glib's subprocesses,
+ so that another thread running glib won't find them. */
+ do
+ have = waitpid (desired, status, WNOHANG | WUNTRACED);
+ while (have < 0 && errno == EINTR);
+ }
+
+ return have == desired;
+}
+
+/* If PID is nonnegative, the child process PID with wait status W has
+ changed its status; record this and return true.
+
+ If PID is negative, ignore W, and look for known child processes
+ of Emacs whose status have changed. For each one found, record its new
+ status.
All we do is change the status; we do not run sentinels or print
notifications. That is saved for the next time keyboard input is
** Malloc WARNING: This should never call malloc either directly or
indirectly; if it does, that is a bug */
-/* Record the changed status of the child process PID with wait status W. */
void
record_child_status_change (pid_t pid, int w)
{
#ifdef SIGCHLD
- Lisp_Object proc;
- struct Lisp_Process *p;
+
+ /* On POSIXish hosts, record at most one child only if we already
+ know one child that has exited. */
+ bool record_at_most_one_child = 0 <= pid;
+
Lisp_Object tail;
/* Find the process that signaled us, and record its status. */
/* The process can have been deleted by Fdelete_process. */
for (tail = deleted_pid_list; CONSP (tail); tail = XCDR (tail))
{
+ bool all_pids_are_fixnums
+ = (MOST_NEGATIVE_FIXNUM <= TYPE_MINIMUM (pid_t)
+ && TYPE_MAXIMUM (pid_t) <= MOST_POSITIVE_FIXNUM);
Lisp_Object xpid = XCAR (tail);
- if ((INTEGERP (xpid) && pid == XINT (xpid))
- || (FLOATP (xpid) && pid == XFLOAT_DATA (xpid)))
+ if (all_pids_are_fixnums ? INTEGERP (xpid) : NUMBERP (xpid))
{
- XSETCAR (tail, Qnil);
- return;
+ pid_t deleted_pid;
+ if (INTEGERP (xpid))
+ deleted_pid = XINT (xpid);
+ else
+ deleted_pid = XFLOAT_DATA (xpid);
+ if (process_status_retrieved (deleted_pid, pid, &w))
+ {
+ XSETCAR (tail, Qnil);
+ if (record_at_most_one_child)
+ return;
+ }
}
}
/* Otherwise, if it is asynchronous, it is in Vprocess_alist. */
- p = 0;
for (tail = Vprocess_alist; CONSP (tail); tail = XCDR (tail))
{
- proc = XCDR (XCAR (tail));
- p = XPROCESS (proc);
- if (EQ (p->type, Qreal) && p->pid == pid)
- break;
- p = 0;
- }
-
- /* Look for an asynchronous process whose pid hasn't been filled
- in yet. */
- if (! p)
- for (tail = Vprocess_alist; CONSP (tail); tail = XCDR (tail))
- {
- proc = XCDR (XCAR (tail));
- p = XPROCESS (proc);
- if (p->pid == -1)
- break;
- p = 0;
- }
+ Lisp_Object proc = XCDR (XCAR (tail));
+ struct Lisp_Process *p = XPROCESS (proc);
+ if (p->alive && process_status_retrieved (p->pid, pid, &w))
+ {
+ /* Change the status of the process that was found. */
+ p->tick = ++process_tick;
+ p->raw_status = w;
+ p->raw_status_new = 1;
- /* Change the status of the process that was found. */
- if (p)
- {
- int clear_desc_flag = 0;
+ /* If process has terminated, stop waiting for its output. */
+ if (WIFSIGNALED (w) || WIFEXITED (w))
+ {
+ int clear_desc_flag = 0;
+ p->alive = 0;
+ if (p->infd >= 0)
+ clear_desc_flag = 1;
- p->tick = ++process_tick;
- p->raw_status = w;
- p->raw_status_new = 1;
+ /* clear_desc_flag avoids a compiler bug in Microsoft C. */
+ if (clear_desc_flag)
+ {
+ FD_CLR (p->infd, &input_wait_mask);
+ FD_CLR (p->infd, &non_keyboard_wait_mask);
+ }
+ }
- /* If process has terminated, stop waiting for its output. */
- if ((WIFSIGNALED (w) || WIFEXITED (w))
- && p->infd >= 0)
- clear_desc_flag = 1;
+ /* Tell wait_reading_process_output that it needs to wake up and
+ look around. */
+ if (input_available_clear_time)
+ *input_available_clear_time = make_emacs_time (0, 0);
- /* We use clear_desc_flag to avoid a compiler bug in Microsoft C. */
- if (clear_desc_flag)
- {
- FD_CLR (p->infd, &input_wait_mask);
- FD_CLR (p->infd, &non_keyboard_wait_mask);
+ if (record_at_most_one_child)
+ return;
}
-
- /* Tell wait_reading_process_output that it needs to wake up and
- look around. */
- if (input_available_clear_time)
- *input_available_clear_time = make_emacs_time (0, 0);
}
- /* There was no asynchronous process found for that pid: we have
- a synchronous process. */
- else
+
+ if (0 <= pid)
{
+ /* The caller successfully waited for a pid but no asynchronous
+ process was found for it, so this is a synchronous process. */
+
synch_process_alive = 0;
/* Report the status of the synchronous process. */
#ifdef SIGCHLD
-/* On some systems, the SIGCHLD handler must return right away. If
- any more processes want to signal us, we will get another signal.
- Otherwise, loop around to use up all the processes that have
- something to tell us. */
-#if (defined WINDOWSNT \
- || (defined USG && !defined GNU_LINUX \
- && !(defined HPUX && defined WNOHANG)))
-enum { CAN_HANDLE_MULTIPLE_CHILDREN = 0 };
-#else
-enum { CAN_HANDLE_MULTIPLE_CHILDREN = 1 };
-#endif
-
static void
handle_child_signal (int sig)
{
- do
- {
- pid_t pid;
- int status;
-
- do
- pid = waitpid (-1, &status, WNOHANG | WUNTRACED);
- while (pid < 0 && errno == EINTR);
-
- /* PID == 0 means no processes found, PID == -1 means a real failure.
- Either way, we have done all our job. */
- if (pid <= 0)
- break;
-
- record_child_status_change (pid, status);
- }
- while (CAN_HANDLE_MULTIPLE_CHILDREN);
+ record_child_status_change (-1, 0);
}
static void
/* Flag to set coding-system of the process buffer from the
coding_system used to decode process output. */
unsigned int inherit_coding_system_flag : 1;
+ /* Whether the process is alive, i.e., can be waited for. Running
+ processes can be waited for, but exited and fake processes cannot. */
+ unsigned int alive : 1;
/* Record the process status in the raw form in which it comes from `wait'.
This is to avoid consing in a signal handler. The `raw_status_new'
flag indicates that `raw_status' contains a new status that still
{
while (1)
{
-#ifdef WINDOWSNT
- wait (0);
- break;
-#else /* not WINDOWSNT */
int status;
int wait_result = waitpid (pid, &status, 0);
if (wait_result < 0)
break;
}
-#endif /* not WINDOWSNT */
+ /* Note: the MS-Windows emulation of waitpid calls QUIT
+ internally. */
if (interruptible)
QUIT;
}
/* Child process management list. */
int child_proc_count = 0;
child_process child_procs[ MAX_CHILDREN ];
-child_process *dead_child = NULL;
static DWORD WINAPI reader_thread (void *arg);
if (cp->pid < 0)
cp->pid = -cp->pid;
- /* pid must fit in a Lisp_Int */
- cp->pid = cp->pid & INTMASK;
-
*pPid = cp->pid;
return TRUE;
delete_child (cp);
}
-/* Wait for any of our existing child processes to die
- When it does, close its handle
- Return the pid and fill in the status if non-NULL. */
+/* Wait for a child process specified by PID, or for any of our
+ existing child processes (if PID is nonpositive) to die. When it
+ does, close its handle. Return the pid of the process that died
+ and fill in STATUS if non-NULL. */
-int
-sys_wait (int *status)
+pid_t
+waitpid (pid_t pid, int *status, int options)
{
DWORD active, retval;
int nh;
- int pid;
child_process *cp, *cps[MAX_CHILDREN];
HANDLE wait_hnd[MAX_CHILDREN];
+ DWORD timeout_ms;
+ int dont_wait = (options & WNOHANG) != 0;
nh = 0;
- if (dead_child != NULL)
+ /* According to Posix:
+
+ PID = -1 means status is requested for any child process.
+
+ PID > 0 means status is requested for a single child process
+ whose pid is PID.
+
+ PID = 0 means status is requested for any child process whose
+ process group ID is equal to that of the calling process. But
+ since Windows has only a limited support for process groups (only
+ for console processes and only for the purposes of passing
+ Ctrl-BREAK signal to them), and since we have no documented way
+ of determining whether a given process belongs to our group, we
+ treat 0 as -1.
+
+ PID < -1 means status is requested for any child process whose
+ process group ID is equal to the absolute value of PID. Again,
+ since we don't support process groups, we treat that as -1. */
+ if (pid > 0)
{
- /* We want to wait for a specific child */
- wait_hnd[nh] = dead_child->procinfo.hProcess;
- cps[nh] = dead_child;
- if (!wait_hnd[nh]) emacs_abort ();
- nh++;
- active = 0;
- goto get_result;
+ int our_child = 0;
+
+ /* We are requested to wait for a specific child. */
+ for (cp = child_procs + (child_proc_count-1); cp >= child_procs; cp--)
+ {
+ /* Some child_procs might be sockets; ignore them. Also
+ ignore subprocesses whose output is not yet completely
+ read. */
+ if (CHILD_ACTIVE (cp)
+ && cp->procinfo.hProcess
+ && cp->pid == pid)
+ {
+ our_child = 1;
+ break;
+ }
+ }
+ if (our_child)
+ {
+ if (cp->fd < 0 || (fd_info[cp->fd].flags & FILE_AT_EOF) != 0)
+ {
+ wait_hnd[nh] = cp->procinfo.hProcess;
+ cps[nh] = cp;
+ nh++;
+ }
+ else if (dont_wait)
+ {
+ /* PID specifies our subprocess, but its status is not
+ yet available. */
+ return 0;
+ }
+ }
+ if (nh == 0)
+ {
+ /* No such child process, or nothing to wait for, so fail. */
+ errno = ECHILD;
+ return -1;
+ }
}
else
{
for (cp = child_procs + (child_proc_count-1); cp >= child_procs; cp--)
- /* some child_procs might be sockets; ignore them */
- if (CHILD_ACTIVE (cp) && cp->procinfo.hProcess
- && (cp->fd < 0 || (fd_info[cp->fd].flags & FILE_AT_EOF) != 0))
- {
- wait_hnd[nh] = cp->procinfo.hProcess;
- cps[nh] = cp;
- nh++;
- }
+ {
+ if (CHILD_ACTIVE (cp)
+ && cp->procinfo.hProcess
+ && (cp->fd < 0 || (fd_info[cp->fd].flags & FILE_AT_EOF) != 0))
+ {
+ wait_hnd[nh] = cp->procinfo.hProcess;
+ cps[nh] = cp;
+ nh++;
+ }
+ }
+ if (nh == 0)
+ {
+ /* Nothing to wait on, so fail. */
+ errno = ECHILD;
+ return -1;
+ }
}
- if (nh == 0)
- {
- /* Nothing to wait on, so fail */
- errno = ECHILD;
- return -1;
- }
+ if (dont_wait)
+ timeout_ms = 0;
+ else
+ timeout_ms = 1000; /* check for quit about once a second. */
do
{
- /* Check for quit about once a second. */
QUIT;
- active = WaitForMultipleObjects (nh, wait_hnd, FALSE, 1000);
+ active = WaitForMultipleObjects (nh, wait_hnd, FALSE, timeout_ms);
} while (active == WAIT_TIMEOUT);
if (active == WAIT_FAILED)
}
if (retval == STILL_ACTIVE)
{
- /* Should never happen */
+ /* Should never happen. */
DebPrint (("Wait.WaitForMultipleObjects returned an active process\n"));
+ if (pid > 0 && dont_wait)
+ return 0;
errno = EINVAL;
return -1;
}
else
retval <<= 8;
+ if (pid > 0 && active != 0)
+ emacs_abort ();
cp = cps[active];
pid = cp->pid;
#ifdef FULL_DEBUG
DebPrint (("select calling SIGCHLD handler for pid %d\n",
cp->pid));
#endif
- dead_child = cp;
sig_handlers[SIGCHLD] (SIGCHLD);
- dead_child = NULL;
}
}
else if (fdindex[active] == -1)
projects / emacs.git / commitdiff