Fix a race condition with glib (Bug#8855).
This is a backport from the trunk, consisting of: 2012-11-17 Eli Zaretskii <email@example.com> * 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 <firstname.lastname@example.org> 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'.
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