Fix race conditions with signal handlers and errno.

Be more systematic about preserving errno whenever a signal
handler returns, even if it's not in the main thread.  Do this by
renaming signal handlers to distinguish between signal delivery
and signal handling.  All uses changed.
* atimer.c (deliver_alarm_signal): Rename from alarm_signal_handler.
* data.c (deliver_arith_signal): Rename from arith_error.
* dispnew.c (deliver_window_change_signal): Rename from
window_change_signal.
* emacs.c (deliver_error_signal): Rename from fatal_error_signal.
(deliver_danger_signal) [SIGDANGER]: Rename from memory_warning_signal.
* keyboard.c (deliver_input_available_signal): Rename from
input_available_signal.
(deliver_user_signal): Rename from handle_user_signal.
(deliver_interrupt_signal): Rename from interrupt_signal.
* process.c (deliver_pipe_signal): Rename from send_process_trap.
(deliver_child_signal): Rename from sigchld_handler.
* atimer.c (handle_alarm_signal):
* data.c (handle_arith_signal):
* dispnew.c (handle_window_change_signal):
* emacs.c (handle_fatal_signal, handle_danger_signal):
* keyboard.c (handle_input_available_signal):
* keyboard.c (handle_user_signal, handle_interrupt_signal):
* process.c (handle_pipe_signal, handle_child_signal):
New functions, with the actual signal-handling code taken from the
original respective signal handlers, sans the sporadic attempts to
preserve errno, since that's now done by handle_on_main_thread.
* atimer.c (alarm_signal_handler): Remove unnecessary decl.
* emacs.c, floatfns.c, lisp.h: Remove unused FLOAT_CATCH_SIGKILL cruft.
* emacs.c (main_thread) [FORWARD_SIGNAL_TO_MAIN_THREAD]:
Move to sysdep.c.
(main) [FORWARD_SIGNAL_TO_MAIN_THREAD]:
Move initialization of main_thread to sysdep.c's init_signals.
* process.c (waitpid) [!WNOHANG]: #define to wait; that's good enough for
our usage, and simplifies the mainline code.
(record_child_status_change): New static function, as a helper
for handle_child_signal, and with most of the old child handler's
contents.
(CAN_HANDLE_MULTIPLE_CHILDREN): New constant.
(handle_child_signal): Use the above.
* sysdep.c (main_thread) [FORWARD_SIGNAL_TO_MAIN_THREAD]:
Moved here from emacs.c.
(init_signals) [FORWARD_SIGNAL_TO_MAIN_THREAD]: Initialize it;
code moved here from emacs.c's main function.
* sysdep.c, syssignal.h (handle_on_main_thread): New function,
replacing the old SIGNAL_THREAD_CHECK.  All uses changed.  This
lets callers save and restore errno properly.

1 files changed, 12 insertions, 12 deletions

diff --git a/src/atimer.c b/src/atimer.c
index eb3136ae55d..060dead9b17 100644
--- a/src/atimer.c
+++ b/src/atimer.c
@@ -41,7 +41,7 @@ static struct atimer *stopped_atimers;
 
 static struct atimer *atimers;
 
-/* Non-zero means alarm_signal_handler has found ripe timers but
+/* Non-zero means alarm signal handler has found ripe timers but
    interrupt_input_blocked was non-zero.  In this case, timer
    functions are not called until the next UNBLOCK_INPUT because timer
    functions are expected to call X, and X cannot be assumed to be
@@ -60,8 +60,6 @@ static void set_alarm (void);
 static void schedule_atimer (struct atimer *);
 static struct atimer *append_atimer_lists (struct atimer *,
                                            struct atimer *);
-static void alarm_signal_handler (int signo);
-
 
 /* Start a new atimer of type TYPE.  TIME specifies when the timer is
    ripe.  FN is the function to call when the timer fires.
@@ -374,13 +372,9 @@ run_timers (void)
 /* Signal handler for SIGALRM.  SIGNO is the signal number, i.e.
    SIGALRM.  */
 
-void
-alarm_signal_handler (int signo)
+static void
+handle_alarm_signal (int sig)
 {
-#ifndef SYNC_INPUT
-  SIGNAL_THREAD_CHECK (signo);
-#endif
-
   pending_atimers = 1;
 #ifdef SYNC_INPUT
   pending_signals = 1;
@@ -389,8 +383,14 @@ alarm_signal_handler (int signo)
 #endif
 }
 
+static void
+deliver_alarm_signal (int sig)
+{
+  handle_on_main_thread (sig, handle_alarm_signal);
+}
+
 
-/* Call alarm_signal_handler for pending timers.  */
+/* Call alarm signal handler for pending timers.  */
 
 void
 do_pending_atimers (void)
@@ -412,7 +412,7 @@ turn_on_atimers (bool on)
 {
   if (on)
     {
-      signal (SIGALRM, alarm_signal_handler);
+      signal (SIGALRM, deliver_alarm_signal);
       set_alarm ();
     }
   else
@@ -426,5 +426,5 @@ init_atimer (void)
   free_atimers = stopped_atimers = atimers = NULL;
   pending_atimers = 0;
   /* pending_signals is initialized in init_keyboard.*/
-  signal (SIGALRM, alarm_signal_handler);
+  signal (SIGALRM, deliver_alarm_signal);
 }