=== modified file 'src/ChangeLog' --- src/ChangeLog 2012-10-28 17:42:52 +0000 +++ src/ChangeLog 2012-10-29 01:25:53 +0000 @@ -1,3 +1,31 @@ +2012-10-28 Paul Eggert + + Fix a race condition that causes Emacs to mess up glib (Bug#8855). + 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. + Perhaps this bug fix can be made more efficient by invoking + waitpid once on a process group instead of invoking it on each + known child, but at least this code fixes the bug. + * 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. + (process_status_retrieved): New function. + (record_child_status_change): Use it. Return bool. + Accept negative 1st argument, which means to wait for one of + the processes that Emacs already knows about. + (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. + * syswait.h: Adjust to above API changes. + 2012-10-28 Eli Zaretskii * w32proc.c (TIMER_TICKS_PER_SEC): New macro. === modified file 'src/process.c' --- src/process.c 2012-10-19 19:25:18 +0000 +++ src/process.c 2012-10-29 01:25:53 +0000 @@ -795,9 +795,8 @@ #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 @@ -1704,16 +1703,7 @@ 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); @@ -6279,9 +6269,30 @@ return process; } -/* 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) + { + 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 a known child process + of Emacs whose status has changed. If one is found, record its new + status and return true; otherwise, return false. 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 @@ -6304,8 +6315,7 @@ ** 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 +bool record_child_status_change (pid_t pid, int w) { #ifdef SIGCHLD @@ -6319,11 +6329,18 @@ for (tail = deleted_pid_list; CONSP (tail); tail = XCDR (tail)) { Lisp_Object xpid = XCAR (tail); - if ((INTEGERP (xpid) && pid == XINT (xpid)) - || (FLOATP (xpid) && pid == XFLOAT_DATA (xpid))) + bool all_pids_are_fixnums + = (MOST_NEGATIVE_FIXNUM <= TYPE_MINIMUM (pid_t) + && TYPE_MAXIMUM (pid_t) <= MOST_POSITIVE_FIXNUM); + pid_t deleted_pid; + if (all_pids_are_fixnums || INTEGERP (xpid)) + deleted_pid = XINT (xpid); + else + deleted_pid = XFLOAT_DATA (xpid); + if (process_status_retrieved (deleted_pid, pid, &w)) { XSETCAR (tail, Qnil); - return; + return 1; } } @@ -6333,23 +6350,11 @@ { proc = XCDR (XCAR (tail)); p = XPROCESS (proc); - if (EQ (p->type, Qreal) && p->pid == pid) + if (EQ (p->type, Qreal) && process_status_retrieved (p->pid, pid, &w)) 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; - } - /* Change the status of the process that was found. */ if (p) { @@ -6375,11 +6380,14 @@ look around. */ if (input_available_clear_time) *input_available_clear_time = make_emacs_time (0, 0); + + return 1; } - /* There was no asynchronous process found for that pid: we have - a synchronous process. */ - else + 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. */ @@ -6392,8 +6400,12 @@ look around. */ if (input_available_clear_time) *input_available_clear_time = make_emacs_time (0, 0); + + return 1; } #endif + + return 0; } #ifdef SIGCHLD @@ -6413,23 +6425,8 @@ 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); + while (record_child_status_change (-1, 0) && CAN_HANDLE_MULTIPLE_CHILDREN) + continue; } static void === modified file 'src/syswait.h' --- src/syswait.h 2012-09-23 22:25:22 +0000 +++ src/syswait.h 2012-10-25 05:29:40 +0000 @@ -23,6 +23,7 @@ #ifndef EMACS_SYSWAIT_H #define EMACS_SYSWAIT_H +#include #include #ifdef HAVE_SYS_WAIT_H /* We have sys/wait.h with POSIXoid definitions. */ @@ -52,7 +53,7 @@ #endif /* Defined in process.c. */ -extern void record_child_status_change (pid_t, int); +extern bool record_child_status_change (pid_t, int); /* Defined in sysdep.c. */ extern void wait_for_termination (pid_t);