Simplify and avoid signal-handling races.

* nt/inc/ms-w32.h (emacs_raise): New macro.
* src/alloc.c (die):
* src/sysdep.c (emacs_abort) [HAVE_NTGUI]:
Avoid recursive loop if there's a fatal error in the function itself.
* src/atimer.c (pending_atimers):
* src/blockinput.h: Don't include "atimer.h"; no longer needed.
(interrupt_input_pending): Remove.  All uses removed.
pending_signals now counts both atimers and ordinary interrupts.
This is less racy than having three separate pending-signal flags.
(block_input, unblock_input, totally_unblock_input, unblock_input_to)
(input_blocked_p):
Rename from their upper-case counterparts BLOCK_INPUT,
UNBLOCK_INPUT, TOTALLY_UNBLOCK_INPUT, UNBLOCK_INPUT_TO,
INPUT_BLOCKED_P, and turn into functions.  All uses changed.
This makes it easier to access volatile variables more accurately.
(BLOCK_INPUT_RESIGNAL): Remove.  All uses replaced by unblock_input ().
(input_blocked_p): Prefer this to 'interrupt_input_blocked', as
that's more reliable if the code is buggy and sets
interrupt_input_blocked to a negative value.  All uses changed.
* src/atimer.c (deliver_alarm_signal):
Remove.  No need to deliver this to the parent; any thread can
handle this signal now.  All uses replaced by underlying handler.
* src/atimer.c (turn_on_atimers):
* src/dispnew.c (handle_window_change_signal):
* src/emacs.c (handle_danger_signal):
* src/keyboard.c (kbd_buffer_get_event):
Don't reestablish signal handler; not needed with sigaction.
* src/blockinput.h (UNBLOCK_INPUT_TO, TOTALLY_UNBLOCK_INPUT)
(UNBLOCK_INPUT_TO):
Rework to avoid unnecessary accesses to volatile variables.
(UNBLOCK_INPUT_TO): Now a function.
(totally_unblock_input, unblock_input): New decls.
* src/data.c (handle_arith_signal, deliver_arith_signal): Move to sysdep.c
(init_data): Remove.  Necessary stuff now done in init_signal.
* src/emacs.c, src/xdisp.c: Include "atimer.h", since we invoke atimer functions.
* src/emacs.c (handle_fatal_signal, deliver_fatal_signal): Move to sysdep.c.
(fatal_error_code): Remove; no longer needed.
(terminate_due_to_signal): Rename from fatal_error_backtrace, since
it doesn't always backtrace.  All uses changed.  No need to reset
signal to default, since sigaction and/or die does that for us now.
Use emacs_raise (FOO), not kill (getpid (), FOO).
(main): Check more-accurately whether we're dumping.
Move fatal-error setup to sysdep.c
* src/floatfns.c: Do not include "syssignal.h"; no longer needed.
* src/gtkutil.c (xg_get_file_name, xg_get_font):
Remove no-longer-needed signal-mask manipulation.
* src/keyboard.c, src/process.c (POLL_FOR_INPUT):
Don't depend on USE_ASYNC_EVENTS, a symbol that is never defined.
* src/keyboard.c (read_avail_input): Remove.
All uses replaced by gobble_input.
(Ftop_level): Use TOTALLY_UNBLOCK_INPUT rather than open code.
(kbd_buffer_store_event_hold, gobble_input):
(record_asynch_buffer_change) [USABLE_SIGIO]:
(store_user_signal_events):
No need to mess with signal mask.
(gobble_input): If blocking input and there are terminals, simply
set pending_signals to 1 and return.  All hooks changed to not
worry about whether input is blocked.
(process_pending_signals): Clear pending_signals before processing
them, in case a signal comes in while we're processing.
By convention callers now test pending_signals before calling us.
(UNBLOCK_INPUT_TO, unblock_input, totally_unblock_input):
New functions, to support changes to blockinput.h.
(handle_input_available_signal): Now extern.
(reinvoke_input_signal): Remove.  All uses replaced by
handle_async_input.
(quit_count): Now volatile, since a signal handler uses it.
(handle_interrupt): Now takes bool IN_SIGNAL_HANDLER as arg.  All
callers changed.  Block SIGINT only if not already blocked.
Clear sigmask reliably, even if Fsignal returns, which it can.
Omit unnecessary accesses to volatile var.
(quit_throw_to_read_char): No need to restore sigmask.
* src/keyboard.c (gobble_input, handle_user_signal):
* src/process.c (wait_reading_process_output):
Call signal-handling code rather than killing ourselves.
* src/lisp.h: Include <float.h>, for...
(IEEE_FLOATING_POINT): New macro, moved here to avoid duplication.
(pending_signals): Now volatile.
(syms_of_data): Now const if IEEE floating point.
(handle_input_available_signal) [USABLE_SIGIO]:
(terminate_due_to_signal, record_child_status_change): New decls.
* src/process.c (create_process): Avoid disaster if memory is exhausted
while we're processing a vfork, by tightening the critical section
around the vfork.
(send_process_frame, process_sent_to, handle_pipe_signal)
(deliver_pipe_signal): Remove.  No longer needed, as Emacs now
ignores SIGPIPE.
(send_process): No need for setjmp/longjmp any more, since the
SIGPIPE stuff is now gone.  Instead, report an error if errno
is EPIPE.
(record_child_status_change): Now extern.  PID and W are now args.
Return void, not bool.  All callers changed.
* src/sysdep.c (wait_debugging) [(BSD_SYSTEM || HPUX) && !defined (__GNU__)]:
Remove.  All uses removed.  This bug should be fixed now in a
different way.
(wait_for_termination_1): Use waitpid rather than sigsuspend,
and record the child status change directly.  This avoids the
need to futz with the signal mask.
(process_fatal_action): Move here from emacs.c.
(emacs_sigaction_flags): New function, containing
much of what used to be in emacs_sigaction_init.
(emacs_sigaction_init): Use it.  Block nonfatal system signals that are
caught by emacs, to make races less likely.
(deliver_process_signal): Rename from handle_on_main_thread.
All uses changed.
(BACKTRACE_LIMIT_MAX): Now at top level.
(thread_backtrace_buffer, threadback_backtrace_pointers):
New static vars.
(deliver_thread_signal, deliver_fatal_thread_signal):
New functions, for more-accurate delivery of thread-specific signals.
(handle_fatal_signal, deliver_fatal_signal): Move here from emacs.c.
(deliver_arith_signal): Handle in this thread, not
in the main thread, since it's triggered by this thread.
(maybe_fatal_sig): New function.
(init_signals): New arg DUMPING so that we can be more accurate
about whether we're dumping.  Caller changed.
Treat thread-specific signals differently from process-general signals.
Block all signals while handling fatal error; that's safer.
xsignal from SIGFPE only on non-IEEE hosts, treating it as fatal
on IEEE hosts.
When batch, ignore SIGHUP, SIGINT, SIGTERM if they were already ignored.
Ignore SIGPIPE unless batch.
(emacs_backtrace): Output backtrace for the appropriate thread,
which is not necessarily the main thread.
* src/syssignal.h: Include <stdbool.h>.
(emacs_raise): New macro.
* src/xterm.c (x_connection_signal): Remove; no longer needed
now that we use sigaction.
(x_connection_closed): No need to mess with sigmask now.
(x_initialize): No need to reset SIGPIPE handler here, since
init_signals does this for us now.

Fixes: debbugs:12471

1 files changed, 36 insertions, 82 deletions

diff --git a/src/blockinput.h b/src/blockinput.h
index 7501bfc91a0..70822e29be7 100644
--- a/src/blockinput.h
+++ b/src/blockinput.h
@@ -19,103 +19,57 @@ along with GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.  */
 #ifndef EMACS_BLOCKINPUT_H
 #define EMACS_BLOCKINPUT_H
 
-#include "atimer.h"
+INLINE_HEADER_BEGIN
+#ifndef BLOCKINPUT_INLINE
+# define BLOCKINPUT_INLINE INLINE
+#endif
 
-/* When Emacs is using signal-driven input, the processing of those
-   input signals can get pretty hairy.  For example, when Emacs is
-   running under X windows, handling an input signal can entail
-   retrieving events from the X event queue, or making other X calls.
-
-   If an input signal occurs while Emacs is in the midst of some
-   non-reentrant code, and the signal processing invokes that same
-   code, we lose.  For example, malloc and the Xlib functions aren't
-   usually re-entrant, and both are used by the X input signal handler
-   - if we try to process an input signal in the midst of executing
-   any of these functions, we'll lose.
+/* Emacs should avoid doing anything hairy in a signal handler, because
+   so many system functions are non-reentrant.  For example, malloc
+   and the Xlib functions aren't usually re-entrant, so if they were
+   used by the SIGIO handler, we'd lose.
 
    To avoid this, we make the following requirements:
 
-   * Everyone must evaluate BLOCK_INPUT before entering these functions,
-   and then call UNBLOCK_INPUT after performing them.  Calls
-   BLOCK_INPUT and UNBLOCK_INPUT may be nested.
+   * Everyone must evaluate BLOCK_INPUT before performing actions that
+   might conflict with a signal handler, and then call UNBLOCK_INPUT
+   after performing them.  Calls BLOCK_INPUT and UNBLOCK_INPUT may be
+   nested.
 
    * Any complicated interrupt handling code should test
-   interrupt_input_blocked, and put off its work until later.
+   INPUT_BLOCKED_P, and put off its work until later.
 
    * If the interrupt handling code wishes, it may set
-   interrupt_input_pending to a non-zero value.  If that flag is set
-   when input becomes unblocked, UNBLOCK_INPUT will send a new SIGIO.  */
-
-extern volatile int interrupt_input_blocked;
-
-/* Nonzero means an input interrupt has arrived
-   during the current critical section.  */
-extern int interrupt_input_pending;
+   pending_signals to a non-zero value.  If that flag is set
+   when input becomes unblocked, UNBLOCK_INPUT will then read
+   input and process timers.
 
+   Historically, Emacs signal handlers did much more than they do now,
+   and this caused many BLOCK_INPUT calls to be sprinkled around the code.
+   FIXME: Remove calls that aren't needed now.  */
 
-/* Non-zero means asynchronous timers should be run when input is
-   unblocked.  */
+extern volatile int interrupt_input_blocked;
 
-extern int pending_atimers;
+/* Begin critical section. */
 
+BLOCKINPUT_INLINE void
+block_input (void)
+{
+  interrupt_input_blocked++;
+}
 
-/* Begin critical section. */
-#define BLOCK_INPUT (interrupt_input_blocked++)
-
-/* End critical section.
-
-   If doing signal-driven input, and a signal came in when input was
-   blocked, reinvoke the signal handler now to deal with it.
-
-   Always test interrupt_input_pending; that's not too expensive, and
-   it'll never get set if we don't need to resignal.  This is simpler
-   than dealing here with every configuration option that might affect
-   whether interrupt_input_pending can be nonzero.  */
-
-#define UNBLOCK_INPUT                           \
-  do                                            \
-    {                                           \
-      --interrupt_input_blocked;                \
-      if (interrupt_input_blocked == 0)         \
-        {                                       \
-          if (interrupt_input_pending)          \
-            reinvoke_input_signal ();           \
-          if (pending_atimers)                  \
-            do_pending_atimers ();              \
-        }                                       \
-      else if (interrupt_input_blocked < 0)     \
-        emacs_abort ();                         \
-    }                                           \
-  while (0)
-
-/* Undo any number of BLOCK_INPUT calls,
-   and also reinvoke any pending signal.  */
-
-#define TOTALLY_UNBLOCK_INPUT                   \
-  do if (interrupt_input_blocked != 0)          \
-    {                                           \
-      interrupt_input_blocked = 1;              \
-      UNBLOCK_INPUT;                            \
-    }                                           \
-  while (0)
-
-/* Undo any number of BLOCK_INPUT calls down to level LEVEL,
-   and also (if the level is now 0) reinvoke any pending signal.  */
-
-#define UNBLOCK_INPUT_TO(LEVEL)                         \
-  do                                                    \
-    {                                                   \
-      interrupt_input_blocked = (LEVEL) + 1;            \
-      UNBLOCK_INPUT;                                    \
-    }                                                   \
-  while (0)
-
-#define UNBLOCK_INPUT_RESIGNAL UNBLOCK_INPUT
+extern void unblock_input (void);
+extern void totally_unblock_input (void);
+extern void unblock_input_to (int);
 
 /* In critical section ? */
-#define INPUT_BLOCKED_P (interrupt_input_blocked > 0)
 
-/* Defined in keyboard.c */
-extern void reinvoke_input_signal (void);
+BLOCKINPUT_INLINE bool
+input_blocked_p (void)
+{
+  return 0 < interrupt_input_blocked;
+}
+
+INLINE_HEADER_END
 
 #endif /* EMACS_BLOCKINPUT_H */