Remove configure's --without-sync-input option.

When auditing signal-handling in preparation for cleaning it up,
I found that SYNC_INPUT has race conditions and would be a real
pain to fix.  Since it's an undocumented and deprecated
configure-time option, now seems like a good time to remove it.
Also see <http://bugs.gnu.org/11080#16>.
* configure.ac (SYNC_INPUT, BROKEN_SA_RESTART): Remove.
* admin/CPP-DEFINES (BROKEN_SA_RESTART, SA_RESTART): Remove.
* etc/TODO (Make SYNC_INPUT the default): Remove, as the code now
behaves as if SYNC_INPUT is always true.
* src/alloc.c (_bytes_used, __malloc_extra_blocks, _malloc_internal)
(_free_internal) [!DOUG_LEA_MALLOC]: Remove decls.
(alloc_mutex) [!SYSTEM_MALLOC && !SYNC_INPUT && HAVE_PTHREAD]:
(malloc_hysteresis):
(check_depth) [XMALLOC_OVERRUN_CHECK]:
(MALLOC_BLOCK_INPUT, MALLOC_UNBLOCK_INPUT):
(__malloc_hook, __realloc_hook, __free_hook, BYTES_USED)
(dont_register_blocks, bytes_used_when_reconsidered)
(bytes_used_when_full, emacs_blocked_free, emacs_blocked_malloc)
(emacs_blocked_realloc, reset_malloc_hooks, uninterrupt_malloc):
[!SYSTEM_MALLOC && !SYNC_INPUT]:
Remove. All uses removed.
(MALLOC_BLOCK_INPUT, MALLOC_UNBLOCK_INPUT): Use a different
implementation, one that depends on whether the new macro
XMALLOC_BLOCK_INPUT_CHECK is defined, not on whether SYNC_INPUT
is defined.
* src/atimer.c (run_timers, handle_alarm_signal):
* src/keyboard.c (pending_signal, poll_for_input_1, poll_for_input)
(handle_async_input, process_pending_signals)
(handle_input_available_signal, init_keyboard):
* src/nsterm.m (ns_read_socket):
* src/process.c (wait_reading_process_output):
* src/regex.c (immediate_quit, IMMEDIATE_QUIT_CHECK):
* src/sysdep.c (emacs_sigaction_init) [SA_RESTART]:
(emacs_write):
* src/xterm.c (XTread_socket):
Assume SYNC_INPUT.
* src/conf_post.h (SA_RESTART) [IRIX6_5]: Do not #undef.
* src/eval.c (handling_signal): Remove.  All uses removed.
* src/lisp.h (ELSE_PENDING_SIGNALS): Remove.
All uses replaced with the SYNC_INPUT version.
(reset_malloc_hooks, uninterrupt_malloc, handling_signal):
Remove decls.
* src/sysdep.c, src/syssignal.h (main_thread) [FORWARD_SIGNAL_TO_MAIN_THREAD]:
Now static.

Fixes: debbugs:12450

18 files changed, 97 insertions, 525 deletions

diff --git a/src/ChangeLog b/src/ChangeLog
index 32cd7b3e813..f21395d9632 100644
--- a/src/ChangeLog
+++ b/src/ChangeLog
@@ -1,5 +1,47 @@
 2012-09-16  Paul Eggert  <eggert@cs.ucla.edu>
 
+        Remove configure's --without-sync-input option (Bug#12450).
+        When auditing signal-handling in preparation for cleaning it up,
+        I found that SYNC_INPUT has race conditions and would be a real
+        pain to fix.  Since it's an undocumented and deprecated
+        configure-time option, now seems like a good time to remove it.
+        Also see <http://bugs.gnu.org/11080#16>.
+        * alloc.c (_bytes_used, __malloc_extra_blocks, _malloc_internal)
+        (_free_internal) [!DOUG_LEA_MALLOC]: Remove decls.
+        (alloc_mutex) [!SYSTEM_MALLOC && !SYNC_INPUT && HAVE_PTHREAD]:
+        (malloc_hysteresis):
+        (check_depth) [XMALLOC_OVERRUN_CHECK]:
+        (MALLOC_BLOCK_INPUT, MALLOC_UNBLOCK_INPUT):
+        (__malloc_hook, __realloc_hook, __free_hook, BYTES_USED)
+        (dont_register_blocks, bytes_used_when_reconsidered)
+        (bytes_used_when_full, emacs_blocked_free, emacs_blocked_malloc)
+        (emacs_blocked_realloc, reset_malloc_hooks, uninterrupt_malloc):
+        [!SYSTEM_MALLOC && !SYNC_INPUT]:
+        Remove. All uses removed.
+        (MALLOC_BLOCK_INPUT, MALLOC_UNBLOCK_INPUT): Use a different
+        implementation, one that depends on whether the new macro
+        XMALLOC_BLOCK_INPUT_CHECK is defined, not on whether SYNC_INPUT
+        is defined.
+        * atimer.c (run_timers, handle_alarm_signal):
+        * keyboard.c (pending_signal, poll_for_input_1, poll_for_input)
+        (handle_async_input, process_pending_signals)
+        (handle_input_available_signal, init_keyboard):
+        * nsterm.m (ns_read_socket):
+        * process.c (wait_reading_process_output):
+        * regex.c (immediate_quit, IMMEDIATE_QUIT_CHECK):
+        * sysdep.c (emacs_sigaction_init) [SA_RESTART]:
+        (emacs_write):
+        * xterm.c (XTread_socket):
+        Assume SYNC_INPUT.
+        * conf_post.h (SA_RESTART) [IRIX6_5]: Do not #undef.
+        * eval.c (handling_signal): Remove.  All uses removed.
+        * lisp.h (ELSE_PENDING_SIGNALS): Remove.
+        All uses replaced with the SYNC_INPUT version.
+        (reset_malloc_hooks, uninterrupt_malloc, handling_signal):
+        Remove decls.
+        * sysdep.c, syssignal.h (main_thread) [FORWARD_SIGNAL_TO_MAIN_THREAD]:
+        Now static.
+
         * font.c (Ffont_shape_gstring): Remove unused local.
 
 2012-09-16  Glenn Morris  <rgm@gnu.org>
diff --git a/src/alloc.c b/src/alloc.c
index 0bfbb0c88b1..fb7d35b5590 100644
--- a/src/alloc.c
+++ b/src/alloc.c
@@ -85,68 +85,8 @@ extern void *sbrk ();
 
 #define MMAP_MAX_AREAS 100000000
 
-#else /* not DOUG_LEA_MALLOC */
-
-/* The following come from gmalloc.c.  */
-
-extern size_t _bytes_used;
-extern size_t __malloc_extra_blocks;
-extern void *_malloc_internal (size_t);
-extern void _free_internal (void *);
-
 #endif /* not DOUG_LEA_MALLOC */
 
-#if ! defined SYSTEM_MALLOC && ! defined SYNC_INPUT
-#ifdef HAVE_PTHREAD
-
-# include "syssignal.h"
-
-/* When GTK uses the file chooser dialog, different backends can be loaded
-   dynamically.  One such a backend is the Gnome VFS backend that gets loaded
-   if you run Gnome.  That backend creates several threads and also allocates
-   memory with malloc.
-
-   Also, gconf and gsettings may create several threads.
-
-   If Emacs sets malloc hooks (! SYSTEM_MALLOC) and the emacs_blocked_*
-   functions below are called from malloc, there is a chance that one
-   of these threads preempts the Emacs main thread and the hook variables
-   end up in an inconsistent state.  So we have a mutex to prevent that (note
-   that the backend handles concurrent access to malloc within its own threads
-   but Emacs code running in the main thread is not included in that control).
-
-   When UNBLOCK_INPUT is called, reinvoke_input_signal may be called.  If this
-   happens in one of the backend threads we will have two threads that tries
-   to run Emacs code at once, and the code is not prepared for that.
-   To prevent that, we only call BLOCK/UNBLOCK from the main thread.  */
-
-static pthread_mutex_t alloc_mutex;
-
-#define BLOCK_INPUT_ALLOC                               \
-  do                                                    \
-    {                                                   \
-      if (pthread_equal (pthread_self (), main_thread)) \
-        BLOCK_INPUT;                                    \
-      pthread_mutex_lock (&alloc_mutex);                \
-    }                                                   \
-  while (0)
-#define UNBLOCK_INPUT_ALLOC                             \
-  do                                                    \
-    {                                                   \
-      pthread_mutex_unlock (&alloc_mutex);              \
-      if (pthread_equal (pthread_self (), main_thread)) \
-        UNBLOCK_INPUT;                                  \
-    }                                                   \
-  while (0)
-
-#else /* ! defined HAVE_PTHREAD */
-
-#define BLOCK_INPUT_ALLOC BLOCK_INPUT
-#define UNBLOCK_INPUT_ALLOC UNBLOCK_INPUT
-
-#endif /* ! defined HAVE_PTHREAD */
-#endif /* ! defined SYSTEM_MALLOC && ! defined SYNC_INPUT */
-
 /* Mark, unmark, query mark bit of a Lisp string.  S must be a pointer
    to a struct Lisp_String.  */
 
@@ -205,10 +145,6 @@ static char *spare_memory[7];
 
 #define SPARE_MEMORY (1 << 14)
 
-/* Number of extra blocks malloc should get when it needs more core.  */
-
-static int malloc_hysteresis;
-
 /* Initialize it to a nonzero value to force it into data space
    (rather than bss space).  That way unexec will remap it into text
    space (pure), on some systems.  We have not implemented the
@@ -413,12 +349,12 @@ static void mark_memory (void *, void *);
 static void mem_init (void);
 static struct mem_node *mem_insert (void *, void *, enum mem_type);
 static void mem_insert_fixup (struct mem_node *);
-#endif
 static void mem_rotate_left (struct mem_node *);
 static void mem_rotate_right (struct mem_node *);
 static void mem_delete (struct mem_node *);
 static void mem_delete_fixup (struct mem_node *);
 static inline struct mem_node *mem_find (void *);
+#endif
 
 
 #if GC_MARK_STACK == GC_MARK_STACK_CHECK_GCPROS
@@ -587,39 +523,17 @@ xmalloc_get_size (unsigned char *ptr)
 }
 
 
-/* The call depth in overrun_check functions.  For example, this might happen:
-   xmalloc()
-     overrun_check_malloc()
-       -> malloc -> (via hook)_-> emacs_blocked_malloc
-          -> overrun_check_malloc
-             call malloc  (hooks are NULL, so real malloc is called).
-             malloc returns 10000.
-             add overhead, return 10016.
-      <- (back in overrun_check_malloc)
-      add overhead again, return 10032
-   xmalloc returns 10032.
-
-   (time passes).
-
-   xfree(10032)
-     overrun_check_free(10032)
-       decrease overhead
-       free(10016)  <-  crash, because 10000 is the original pointer.  */
-
-static ptrdiff_t check_depth;
-
 /* Like malloc, but wraps allocated block with header and trailer.  */
 
 static void *
 overrun_check_malloc (size_t size)
 {
   register unsigned char *val;
-  int overhead = ++check_depth == 1 ? XMALLOC_OVERRUN_CHECK_OVERHEAD : 0;
-  if (SIZE_MAX - overhead < size)
+  if (SIZE_MAX - XMALLOC_OVERRUN_CHECK_OVERHEAD < size)
     emacs_abort ();
 
-  val = malloc (size + overhead);
-  if (val && check_depth == 1)
+  val = malloc (size + XMALLOC_OVERRUN_CHECK_OVERHEAD);
+  if (val)
     {
       memcpy (val, xmalloc_overrun_check_header, XMALLOC_OVERRUN_CHECK_SIZE);
       val += XMALLOC_OVERRUN_CHECK_SIZE + XMALLOC_OVERRUN_SIZE_SIZE;
@@ -627,7 +541,6 @@ overrun_check_malloc (size_t size)
       memcpy (val + size, xmalloc_overrun_check_trailer,
               XMALLOC_OVERRUN_CHECK_SIZE);
     }
-  --check_depth;
   return val;
 }
 
@@ -639,12 +552,10 @@ static void *
 overrun_check_realloc (void *block, size_t size)
 {
   register unsigned char *val = (unsigned char *) block;
-  int overhead = ++check_depth == 1 ? XMALLOC_OVERRUN_CHECK_OVERHEAD : 0;
-  if (SIZE_MAX - overhead < size)
+  if (SIZE_MAX - XMALLOC_OVERRUN_CHECK_OVERHEAD < size)
     emacs_abort ();
 
   if (val
-      && check_depth == 1
       && memcmp (xmalloc_overrun_check_header,
                  val - XMALLOC_OVERRUN_CHECK_SIZE - XMALLOC_OVERRUN_SIZE_SIZE,
                  XMALLOC_OVERRUN_CHECK_SIZE) == 0)
@@ -658,9 +569,9 @@ overrun_check_realloc (void *block, size_t size)
       memset (val, 0, XMALLOC_OVERRUN_CHECK_SIZE + XMALLOC_OVERRUN_SIZE_SIZE);
     }
 
-  val = realloc (val, size + overhead);
+  val = realloc (val, size + XMALLOC_OVERRUN_CHECK_OVERHEAD);
 
-  if (val && check_depth == 1)
+  if (val)
     {
       memcpy (val, xmalloc_overrun_check_header, XMALLOC_OVERRUN_CHECK_SIZE);
       val += XMALLOC_OVERRUN_CHECK_SIZE + XMALLOC_OVERRUN_SIZE_SIZE;
@@ -668,7 +579,6 @@ overrun_check_realloc (void *block, size_t size)
       memcpy (val + size, xmalloc_overrun_check_trailer,
               XMALLOC_OVERRUN_CHECK_SIZE);
     }
-  --check_depth;
   return val;
 }
 
@@ -679,9 +589,7 @@ overrun_check_free (void *block)
 {
   unsigned char *val = (unsigned char *) block;
 
-  ++check_depth;
   if (val
-      && check_depth == 1
       && memcmp (xmalloc_overrun_check_header,
                  val - XMALLOC_OVERRUN_CHECK_SIZE - XMALLOC_OVERRUN_SIZE_SIZE,
                  XMALLOC_OVERRUN_CHECK_SIZE) == 0)
@@ -701,7 +609,6 @@ overrun_check_free (void *block)
     }
 
   free (val);
-  --check_depth;
 }
 
 #undef malloc
@@ -712,14 +619,33 @@ overrun_check_free (void *block)
 #define free overrun_check_free
 #endif
 
-#ifdef SYNC_INPUT
-/* When using SYNC_INPUT, we don't call malloc from a signal handler, so
-   there's no need to block input around malloc.  */
-#define MALLOC_BLOCK_INPUT   ((void)0)
-#define MALLOC_UNBLOCK_INPUT ((void)0)
+/* If compiled with XMALLOC_BLOCK_INPUT_CHECK, define a symbol
+   BLOCK_INPUT_IN_MEMORY_ALLOCATORS that is visible to the debugger.
+   If that variable is set, block input while in one of Emacs's memory
+   allocation functions.  There should be no need for this debugging
+   option, since signal handlers do not allocate memory, but Emacs
+   formerly allocated memory in signal handlers and this compile-time
+   option remains as a way to help debug the issue should it rear its
+   ugly head again.  */
+#ifdef XMALLOC_BLOCK_INPUT_CHECK
+bool block_input_in_memory_allocators EXTERNALLY_VISIBLE;
+static void
+malloc_block_input (void)
+{
+  if (block_input_in_memory_allocators)
+    BLOCK_INPUT;
+}
+static void
+malloc_unblock_input (void)
+{
+  if (block_input_in_memory_allocators)
+    UNBLOCK_INPUT;
+}
+# define MALLOC_BLOCK_INPUT malloc_block_input ()
+# define MALLOC_UNBLOCK_INPUT malloc_unblock_input ()
 #else
-#define MALLOC_BLOCK_INPUT   BLOCK_INPUT
-#define MALLOC_UNBLOCK_INPUT UNBLOCK_INPUT
+# define MALLOC_BLOCK_INPUT ((void) 0)
+# define MALLOC_UNBLOCK_INPUT ((void) 0)
 #endif
 
 /* Like malloc but check for no memory and block interrupt input..  */
@@ -788,8 +714,7 @@ xfree (void *block)
   free (block);
   MALLOC_UNBLOCK_INPUT;
   /* We don't call refill_memory_reserve here
-     because that duplicates doing so in emacs_blocked_free
-     and the criterion should go there.  */
+     because in practice the call in r_alloc_free seems to suffice.  */
 }
 
 
@@ -1216,256 +1141,6 @@ lisp_align_free (void *block)
 }
 
 
-#ifndef SYSTEM_MALLOC
-
-/* Arranging to disable input signals while we're in malloc.
-
-   This only works with GNU malloc.  To help out systems which can't
-   use GNU malloc, all the calls to malloc, realloc, and free
-   elsewhere in the code should be inside a BLOCK_INPUT/UNBLOCK_INPUT
-   pair; unfortunately, we have no idea what C library functions
-   might call malloc, so we can't really protect them unless you're
-   using GNU malloc.  Fortunately, most of the major operating systems
-   can use GNU malloc.  */
-
-#ifndef SYNC_INPUT
-/* When using SYNC_INPUT, we don't call malloc from a signal handler, so
-   there's no need to block input around malloc.  */
-
-#ifndef DOUG_LEA_MALLOC
-extern void * (*__malloc_hook) (size_t, const void *);
-extern void * (*__realloc_hook) (void *, size_t, const void *);
-extern void (*__free_hook) (void *, const void *);
-/* Else declared in malloc.h, perhaps with an extra arg.  */
-#endif /* DOUG_LEA_MALLOC */
-static void * (*old_malloc_hook) (size_t, const void *);
-static void * (*old_realloc_hook) (void *,  size_t, const void*);
-static void (*old_free_hook) (void*, const void*);
-
-#ifdef DOUG_LEA_MALLOC
-#  define BYTES_USED (mallinfo ().uordblks)
-#else
-#  define BYTES_USED _bytes_used
-#endif
-
-#ifdef GC_MALLOC_CHECK
-static bool dont_register_blocks;
-#endif
-
-static size_t bytes_used_when_reconsidered;
-
-/* Value of _bytes_used, when spare_memory was freed.  */
-
-static size_t bytes_used_when_full;
-
-/* This function is used as the hook for free to call.  */
-
-static void
-emacs_blocked_free (void *ptr, const void *ptr2)
-{
-  BLOCK_INPUT_ALLOC;
-
-#ifdef GC_MALLOC_CHECK
-  if (ptr)
-    {
-      struct mem_node *m;
-
-      m = mem_find (ptr);
-      if (m == MEM_NIL || m->start != ptr)
-        {
-          fprintf (stderr,
-                   "Freeing `%p' which wasn't allocated with malloc\n", ptr);
-          emacs_abort ();
-        }
-      else
-        {
-          /* fprintf (stderr, "free %p...%p (%p)\n", m->start, m->end, ptr); */
-          mem_delete (m);
-        }
-    }
-#endif /* GC_MALLOC_CHECK */
-
-  __free_hook = old_free_hook;
-  free (ptr);
-
-  /* If we released our reserve (due to running out of memory),
-     and we have a fair amount free once again,
-     try to set aside another reserve in case we run out once more.  */
-  if (! NILP (Vmemory_full)
-      /* Verify there is enough space that even with the malloc
-         hysteresis this call won't run out again.
-         The code here is correct as long as SPARE_MEMORY
-         is substantially larger than the block size malloc uses.  */
-      && (bytes_used_when_full
-          > ((bytes_used_when_reconsidered = BYTES_USED)
-             + max (malloc_hysteresis, 4) * SPARE_MEMORY)))
-    refill_memory_reserve ();
-
-  __free_hook = emacs_blocked_free;
-  UNBLOCK_INPUT_ALLOC;
-}
-
-
-/* This function is the malloc hook that Emacs uses.  */
-
-static void *
-emacs_blocked_malloc (size_t size, const void *ptr)
-{
-  void *value;
-
-  BLOCK_INPUT_ALLOC;
-  __malloc_hook = old_malloc_hook;
-#ifdef DOUG_LEA_MALLOC
-  /* Segfaults on my system.  --lorentey */
-  /* mallopt (M_TOP_PAD, malloc_hysteresis * 4096); */
-#else
-    __malloc_extra_blocks = malloc_hysteresis;
-#endif
-
-  value = malloc (size);
-
-#ifdef GC_MALLOC_CHECK
-  {
-    struct mem_node *m = mem_find (value);
-    if (m != MEM_NIL)
-      {
-        fprintf (stderr, "Malloc returned %p which is already in use\n",
-                 value);
-        fprintf (stderr, "Region in use is %p...%p, %td bytes, type %d\n",
-                 m->start, m->end, (char *) m->end - (char *) m->start,
-                 m->type);
-        emacs_abort ();
-      }
-
-    if (!dont_register_blocks)
-      {
-        mem_insert (value, (char *) value + max (1, size), allocated_mem_type);
-        allocated_mem_type = MEM_TYPE_NON_LISP;
-      }
-  }
-#endif /* GC_MALLOC_CHECK */
-
-  __malloc_hook = emacs_blocked_malloc;
-  UNBLOCK_INPUT_ALLOC;
-
-  /* fprintf (stderr, "%p malloc\n", value); */
-  return value;
-}
-
-
-/* This function is the realloc hook that Emacs uses.  */
-
-static void *
-emacs_blocked_realloc (void *ptr, size_t size, const void *ptr2)
-{
-  void *value;
-
-  BLOCK_INPUT_ALLOC;
-  __realloc_hook = old_realloc_hook;
-
-#ifdef GC_MALLOC_CHECK
-  if (ptr)
-    {
-      struct mem_node *m = mem_find (ptr);
-      if (m == MEM_NIL || m->start != ptr)
-        {
-          fprintf (stderr,
-                   "Realloc of %p which wasn't allocated with malloc\n",
-                   ptr);
-          emacs_abort ();
-        }
-
-      mem_delete (m);
-    }
-
-  /* fprintf (stderr, "%p -> realloc\n", ptr); */
-
-  /* Prevent malloc from registering blocks.  */
-  dont_register_blocks = 1;
-#endif /* GC_MALLOC_CHECK */
-
-  value = realloc (ptr, size);
-
-#ifdef GC_MALLOC_CHECK
-  dont_register_blocks = 0;
-
-  {
-    struct mem_node *m = mem_find (value);
-    if (m != MEM_NIL)
-      {
-        fprintf (stderr, "Realloc returns memory that is already in use\n");
-        emacs_abort ();
-      }
-
-    /* Can't handle zero size regions in the red-black tree.  */
-    mem_insert (value, (char *) value + max (size, 1), MEM_TYPE_NON_LISP);
-  }
-
-  /* fprintf (stderr, "%p <- realloc\n", value); */
-#endif /* GC_MALLOC_CHECK */
-
-  __realloc_hook = emacs_blocked_realloc;
-  UNBLOCK_INPUT_ALLOC;
-
-  return value;
-}
-
-
-#ifdef HAVE_PTHREAD
-/* Called from Fdump_emacs so that when the dumped Emacs starts, it has a
-   normal malloc.  Some thread implementations need this as they call
-   malloc before main.  The pthread_self call in BLOCK_INPUT_ALLOC then
-   calls malloc because it is the first call, and we have an endless loop.  */
-
-void
-reset_malloc_hooks (void)
-{
-  __free_hook = old_free_hook;
-  __malloc_hook = old_malloc_hook;
-  __realloc_hook = old_realloc_hook;
-}
-#endif /* HAVE_PTHREAD */
-
-
-/* Called from main to set up malloc to use our hooks.  */
-
-void
-uninterrupt_malloc (void)
-{
-#ifdef HAVE_PTHREAD
-#ifdef DOUG_LEA_MALLOC
-  pthread_mutexattr_t attr;
-
-  /*  GLIBC has a faster way to do this, but let's keep it portable.
-      This is according to the Single UNIX Specification.  */
-  pthread_mutexattr_init (&attr);
-  pthread_mutexattr_settype (&attr, PTHREAD_MUTEX_RECURSIVE);
-  pthread_mutex_init (&alloc_mutex, &attr);
-#else  /* !DOUG_LEA_MALLOC */
-  /* Some systems such as Solaris 2.6 don't have a recursive mutex,
-     and the bundled gmalloc.c doesn't require it.  */
-  pthread_mutex_init (&alloc_mutex, NULL);
-#endif /* !DOUG_LEA_MALLOC */
-#endif /* HAVE_PTHREAD */
-
-  if (__free_hook != emacs_blocked_free)
-    old_free_hook = __free_hook;
-  __free_hook = emacs_blocked_free;
-
-  if (__malloc_hook != emacs_blocked_malloc)
-    old_malloc_hook = __malloc_hook;
-  __malloc_hook = emacs_blocked_malloc;
-
-  if (__realloc_hook != emacs_blocked_realloc)
-    old_realloc_hook = __realloc_hook;
-  __realloc_hook = emacs_blocked_realloc;
-}
-
-#endif /* not SYNC_INPUT */
-#endif /* not SYSTEM_MALLOC */
-
-
-
 /***********************************************************************
                          Interval Allocation
  ***********************************************************************/
@@ -1511,8 +1186,6 @@ make_interval (void)
 {
   INTERVAL val;
 
-  /* eassert (!handling_signal); */
-
   MALLOC_BLOCK_INPUT;
 
   if (interval_free_list)
@@ -1896,8 +1569,6 @@ allocate_string (void)
 {
   struct Lisp_String *s;
 
-  /* eassert (!handling_signal); */
-
   MALLOC_BLOCK_INPUT;
 
   /* If the free-list is empty, allocate a new string_block, and
@@ -2589,8 +2260,6 @@ make_float (double float_value)
 {
   register Lisp_Object val;
 
-  /* eassert (!handling_signal); */
-
   MALLOC_BLOCK_INPUT;
 
   if (float_free_list)
@@ -2698,8 +2367,6 @@ DEFUN ("cons", Fcons, Scons, 2, 2, 0,
 {
   register Lisp_Object val;
 
-  /* eassert (!handling_signal); */
-
   MALLOC_BLOCK_INPUT;
 
   if (cons_free_list)
@@ -3205,9 +2872,6 @@ allocate_vectorlike (ptrdiff_t len)
 
   MALLOC_BLOCK_INPUT;
 
-  /* This gets triggered by code which I haven't bothered to fix.  --Stef  */
-  /* eassert (!handling_signal); */
-
   if (len == 0)
     p = XVECTOR (zero_vector);
   else
@@ -3492,8 +3156,6 @@ Its value and function definition are void, and its property list is nil.  */)
 
   CHECK_STRING (name);
 
-  /* eassert (!handling_signal); */
-
   MALLOC_BLOCK_INPUT;
 
   if (symbol_free_list)
@@ -3578,8 +3240,6 @@ allocate_misc (enum Lisp_Misc_Type type)
 {
   Lisp_Object val;
 
-  /* eassert (!handling_signal); */
-
   MALLOC_BLOCK_INPUT;
 
   if (marker_free_list)
@@ -3799,12 +3459,6 @@ memory_full (size_t nbytes)
               lisp_free (spare_memory[i]);
             spare_memory[i] = 0;
           }
-
-      /* Record the space now used.  When it decreases substantially,
-         we can refill the memory reserve.  */
-#if !defined SYSTEM_MALLOC && !defined SYNC_INPUT
-      bytes_used_when_full = BYTES_USED;
-#endif
     }
 
   /* This used to call error, but if we've run out of memory, we could
@@ -3942,7 +3596,7 @@ mem_insert (void *start, void *end, enum mem_type type)
 
   /* Create a new node.  */
 #ifdef GC_MALLOC_CHECK
-  x = _malloc_internal (sizeof *x);
+  x = malloc (sizeof *x);
   if (x == NULL)
     emacs_abort ();
 #else
@@ -4166,7 +3820,7 @@ mem_delete (struct mem_node *z)
     mem_delete_fixup (x);
 
 #ifdef GC_MALLOC_CHECK
-  _free_internal (y);
+  free (y);
 #else
   xfree (y);
 #endif
@@ -6767,12 +6421,6 @@ init_alloc_once (void)
   init_strings ();
   init_vectors ();
 
-#ifdef REL_ALLOC
-  malloc_hysteresis = 32;
-#else
-  malloc_hysteresis = 0;
-#endif
-
   refill_memory_reserve ();
   gc_cons_threshold = GC_DEFAULT_THRESHOLD;
 }
diff --git a/src/atimer.c b/src/atimer.c
index 80b813fe4fe..5dbd807872a 100644
--- a/src/atimer.c
+++ b/src/atimer.c
@@ -369,7 +369,6 @@ run_timers (void)
   if (! atimers)
     pending_atimers = 0;
 
-#ifdef SYNC_INPUT
   if (pending_atimers)
     pending_signals = 1;
   else
@@ -377,10 +376,6 @@ run_timers (void)
       pending_signals = interrupt_input_pending;
       set_alarm ();
     }
-#else
-  if (! pending_atimers)
-    set_alarm ();
-#endif
 }
 
 
@@ -391,11 +386,7 @@ static void
 handle_alarm_signal (int sig)
 {
   pending_atimers = 1;
-#ifdef SYNC_INPUT
   pending_signals = 1;
-#else
-  run_timers ();
-#endif
 }
 
 static void
diff --git a/src/bytecode.c b/src/bytecode.c
index b151078f60f..5f4fdcc5eff 100644
--- a/src/bytecode.c
+++ b/src/bytecode.c
@@ -458,7 +458,8 @@ unmark_byte_stack (void)
         Fsignal (Qquit, Qnil);                          \
         AFTER_POTENTIAL_GC ();                          \
       }                                                 \
-    ELSE_PENDING_SIGNALS                                \
+    else if (pending_signals)                           \
+      process_pending_signals ();                       \
   } while (0)
 
 
diff --git a/src/conf_post.h b/src/conf_post.h
index 94934ffeadf..0c4d029bc5d 100644
--- a/src/conf_post.h
+++ b/src/conf_post.h
@@ -90,7 +90,6 @@ along with GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.  */
 char *_getpty();
 #endif
 
-#undef SA_RESTART     /* not the same as defining BROKEN_SA_RESTART */
 #endif /* IRIX6_5 */
 
 #ifdef MSDOS
diff --git a/src/emacs.c b/src/emacs.c
index 1416bf76c43..233c0e68a14 100644
--- a/src/emacs.c
+++ b/src/emacs.c
@@ -848,14 +848,10 @@ main (int argc, char **argv)
   /* Arrange to get warning messages as memory fills up.  */
   memory_warnings (0, malloc_warning);
 
-  /* Call malloc at least once, to run the initial __malloc_hook.
+  /* Call malloc at least once, to run malloc_initialize_hook.
      Also call realloc and free for consistency.  */
   free (realloc (malloc (4), 4));
 
-# ifndef SYNC_INPUT
-  /* Arrange to disable interrupt input inside malloc etc.  */
-  uninterrupt_malloc ();
-# endif /* not SYNC_INPUT */
 #endif  /* not SYSTEM_MALLOC */
 
 #if defined (MSDOS) || defined (WINDOWSNT)
@@ -2143,12 +2139,6 @@ You must run Emacs in batch mode in order to dump it.  */)
     memory_warnings (my_edata, malloc_warning);
   }
 #endif /* not WINDOWSNT */
-#if defined (HAVE_PTHREAD) && !defined SYNC_INPUT
-  /* Pthread may call malloc before main, and then we will get an endless
-     loop, because pthread_self (see alloc.c) calls malloc the first time
-     it is called on some systems.  */
-  reset_malloc_hooks ();
-#endif
 #endif /* not SYSTEM_MALLOC */
 #ifdef DOUG_LEA_MALLOC
   malloc_state_ptr = malloc_get_state ();
diff --git a/src/eval.c b/src/eval.c
index 6cca13a8fda..1c565e233c6 100644
--- a/src/eval.c
+++ b/src/eval.c
@@ -117,12 +117,6 @@ static EMACS_INT when_entered_debugger;
 
 Lisp_Object Vsignaling_function;
 
-/* Set to non-zero while processing X events.  Checked in Feval to
-   make sure the Lisp interpreter isn't called from a signal handler,
-   which is unsafe because the interpreter isn't reentrant.  */
-
-int handling_signal;
-
 /* If non-nil, Lisp code must not be run since some part of Emacs is
    in an inconsistent state.  Currently, x-create-frame uses this to
    avoid triggering window-configuration-change-hook while the new
@@ -1106,7 +1100,6 @@ unwind_to_catch (struct catchtag *catch, Lisp_Object value)
   /* Restore certain special C variables.  */
   set_poll_suppress_count (catch->poll_suppress_count);
   UNBLOCK_INPUT_TO (catch->interrupt_input_blocked);
-  handling_signal = 0;
   immediate_quit = 0;
 
   do
@@ -1486,7 +1479,7 @@ See also the function `condition-case'.  */)
   struct handler *h;
   struct backtrace *bp;
 
-  immediate_quit = handling_signal = 0;
+  immediate_quit = 0;
   abort_on_gc = 0;
   if (gc_in_progress || waiting_for_input)
     emacs_abort ();
@@ -2039,9 +2032,6 @@ eval_sub (Lisp_Object form)
   struct backtrace backtrace;
   struct gcpro gcpro1, gcpro2, gcpro3;
 
-  if (handling_signal)
-    emacs_abort ();
-
   if (SYMBOLP (form))
     {
       /* Look up its binding in the lexical environment.
@@ -3104,8 +3094,6 @@ specbind (Lisp_Object symbol, Lisp_Object value)
 {
   struct Lisp_Symbol *sym;
 
-  eassert (!handling_signal);
-
   CHECK_SYMBOL (symbol);
   sym = XSYMBOL (symbol);
   if (specpdl_ptr == specpdl + specpdl_size)
@@ -3199,8 +3187,6 @@ specbind (Lisp_Object symbol, Lisp_Object value)
 void
 record_unwind_protect (Lisp_Object (*function) (Lisp_Object), Lisp_Object arg)
 {
-  eassert (!handling_signal);
-
   if (specpdl_ptr == specpdl + specpdl_size)
     grow_specpdl ();
   specpdl_ptr->func = function;
diff --git a/src/intervals.c b/src/intervals.c
index 5a47cacb2dd..584ee1e923d 100644
--- a/src/intervals.c
+++ b/src/intervals.c
@@ -673,8 +673,7 @@ find_interval (register INTERVAL tree, register ptrdiff_t position)
 
   eassert (relative_position <= TOTAL_LENGTH (tree));
 
-  if (!handling_signal)
-    tree = balance_possible_root_interval (tree);
+  tree = balance_possible_root_interval (tree);
 
   while (1)
     {
diff --git a/src/keyboard.c b/src/keyboard.c
index d164083fb86..01644b3832d 100644
--- a/src/keyboard.c
+++ b/src/keyboard.c
@@ -84,9 +84,7 @@ int interrupt_input_pending;
    pending_atimers separately, to reduce code size.  So, any code that
    changes interrupt_input_pending or pending_atimers should update
    this too.  */
-#ifdef SYNC_INPUT
 int pending_signals;
-#endif
 
 #define KBD_BUFFER_SIZE 4096
 
@@ -2010,17 +2008,9 @@ static struct atimer *poll_timer;
 void
 poll_for_input_1 (void)
 {
-/* Tell ns_read_socket() it is being called asynchronously so it can avoid
-   doing anything dangerous.  */
-#ifdef HAVE_NS
-  ++handling_signal;
-#endif
   if (interrupt_input_blocked == 0
       && !waiting_for_input)
     read_avail_input (0);
-#ifdef HAVE_NS
-  --handling_signal;
-#endif
 }
 
 /* Timer callback function for poll_timer.  TIMER is equal to
@@ -2031,12 +2021,8 @@ poll_for_input (struct atimer *timer)
 {
   if (poll_suppress_count == 0)
     {
-#ifdef SYNC_INPUT
       interrupt_input_pending = 1;
       pending_signals = 1;
-#else
-      poll_for_input_1 ();
-#endif
     }
 }
 
@@ -7176,19 +7162,12 @@ tty_read_avail_input (struct terminal *terminal,
   return nread;
 }
 
-#if defined SYNC_INPUT || defined USABLE_SIGIO
 static void
 handle_async_input (void)
 {
   interrupt_input_pending = 0;
-#ifdef SYNC_INPUT
   pending_signals = pending_atimers;
-#endif
-/* Tell ns_read_socket() it is being called asynchronously so it can avoid
-   doing anything dangerous.  */
-#ifdef HAVE_NS
-  ++handling_signal;
-#endif
+
   while (1)
     {
       int nread;
@@ -7199,13 +7178,8 @@ handle_async_input (void)
       if (nread <= 0)
         break;
     }
-#ifdef HAVE_NS
-  --handling_signal;
-#endif
 }
-#endif /* SYNC_INPUT || USABLE_SIGIO */
 
-#ifdef SYNC_INPUT
 void
 process_pending_signals (void)
 {
@@ -7213,24 +7187,17 @@ process_pending_signals (void)
     handle_async_input ();
   do_pending_atimers ();
 }
-#endif
 
 #ifdef USABLE_SIGIO
 
 static void
 handle_input_available_signal (int sig)
 {
-#ifdef SYNC_INPUT
   interrupt_input_pending = 1;
   pending_signals = 1;
-#endif
 
   if (input_available_clear_time)
     *input_available_clear_time = make_emacs_time (0, 0);
-
-#ifndef SYNC_INPUT
-  handle_async_input ();
-#endif
 }
 
 static void
@@ -11365,9 +11332,7 @@ init_keyboard (void)
   input_pending = 0;
   interrupt_input_blocked = 0;
   interrupt_input_pending = 0;
-#ifdef SYNC_INPUT
   pending_signals = 0;
-#endif
 
   /* This means that command_loop_1 won't try to select anything the first
      time through.  */
diff --git a/src/lisp.h b/src/lisp.h
index 447c6bd296b..3a473a60b48 100644
--- a/src/lisp.h
+++ b/src/lisp.h
@@ -2107,22 +2107,16 @@ extern char *stack_bottom;
    If quit-flag is set to `kill-emacs' the SIGINT handler has received
    a request to exit Emacs when it is safe to do.  */
 
-#ifdef SYNC_INPUT
 extern void process_pending_signals (void);
 extern int pending_signals;
-#define ELSE_PENDING_SIGNALS                            \
-  else if (pending_signals)                             \
-    process_pending_signals ();
-#else  /* not SYNC_INPUT */
-#define ELSE_PENDING_SIGNALS
-#endif  /* not SYNC_INPUT */
 
 extern void process_quit_flag (void);
 #define QUIT                                            \
   do {                                                  \
     if (!NILP (Vquit_flag) && NILP (Vinhibit_quit))     \
       process_quit_flag ();                             \
-    ELSE_PENDING_SIGNALS                                \
+    else if (pending_signals)                           \
+      process_pending_signals ();                       \
   } while (0)
 
 
@@ -2846,8 +2840,6 @@ extern void memory_warnings (void *, void (*warnfun) (const char *));
 /* Defined in alloc.c.  */
 extern void check_pure_size (void);
 extern void allocate_string_data (struct Lisp_String *, EMACS_INT, EMACS_INT);
-extern void reset_malloc_hooks (void);
-extern void uninterrupt_malloc (void);
 extern void malloc_warning (const char *);
 extern _Noreturn void memory_full (size_t);
 extern _Noreturn void buffer_memory_full (ptrdiff_t);
@@ -3043,7 +3035,6 @@ extern Lisp_Object Qand_rest;
 extern Lisp_Object Vautoload_queue;
 extern Lisp_Object Vsignaling_function;
 extern Lisp_Object inhibit_lisp_code;
-extern int handling_signal;
 #if BYTE_MARK_STACK
 extern struct catchtag *catchlist;
 extern struct handler *handlerlist;
diff --git a/src/nsmenu.m b/src/nsmenu.m
index 3057f4f6a20..907d3eac622 100644
--- a/src/nsmenu.m
+++ b/src/nsmenu.m
@@ -588,10 +588,7 @@ extern NSString *NSMenuDidBeginTrackingNotification;
      From 10.6 on, we could also use -[NSMenu propertiesToUpdate]: In the
      key press case, NSMenuPropertyItemImage (e.g.) won't be set.
   */
-  if (trackingMenu == 0
-      /* Also, don't try this if from an event picked up asynchronously,
-         as lots of lisp evaluation happens in ns_update_menubar. */
-      || handling_signal != 0)
+  if (trackingMenu == 0)
     return;
 /*fprintf (stderr, "Updating menu '%s'\n", [[self title] UTF8String]); NSLog (@"%@\n", event); */
   ns_update_menubar (frame, 1, self);
diff --git a/src/nsterm.m b/src/nsterm.m
index 41520ce74d1..0b26508dbd0 100644
--- a/src/nsterm.m
+++ b/src/nsterm.m
@@ -3355,16 +3355,12 @@ ns_read_socket (struct terminal *terminal, int expected,
   if (interrupt_input_blocked)
     {
       interrupt_input_pending = 1;
-#ifdef SYNC_INPUT
       pending_signals = 1;
-#endif
       return -1;
     }
 
   interrupt_input_pending = 0;
-#ifdef SYNC_INPUT
   pending_signals = pending_atimers;
-#endif
 
   BLOCK_INPUT;
   n_emacs_events_pending = 0;
@@ -3726,7 +3722,7 @@ ns_judge_scroll_bars (struct frame *f)
       removed = YES;
     }
 
-  if (removed) 
+  if (removed)
     [eview updateFrameSize: NO];
 }
 
@@ -3988,7 +3984,6 @@ ns_term_init (Lisp_Object display_name)
   /* count object allocs (About, click icon); on OS X use ObjectAlloc tool */
   /*GSDebugAllocationActive (YES); */
   BLOCK_INPUT;
-  handling_signal = 0;
 
   baud_rate = 38400;
   Fset_input_interrupt_mode (Qnil);
@@ -6239,7 +6234,7 @@ not_in_argv (NSString *arg)
       NSRect r = [super constrainFrameRect:frameRect toScreen:screen];
       return r;
     }
-  
+
   if (f->output_data.ns->dont_constrain
       || ns_menu_bar_should_be_hidden ())
     return frameRect;
diff --git a/src/process.c b/src/process.c
index 6dbff6f4b16..a371dece250 100644
--- a/src/process.c
+++ b/src/process.c
@@ -4395,10 +4395,8 @@ wait_reading_process_output (intmax_t time_limit, int nsecs, int read_kbd,
          Otherwise, do pending quit if requested.  */
       if (read_kbd >= 0)
         QUIT;
-#ifdef SYNC_INPUT
       else
         process_pending_signals ();
-#endif
 
       /* Exit now if the cell we're waiting for became non-nil.  */
       if (! NILP (wait_for_cell) && ! NILP (XCAR (wait_for_cell)))
diff --git a/src/regex.c b/src/regex.c
index 92264ccae23..17562043df1 100644
--- a/src/regex.c
+++ b/src/regex.c
@@ -1831,9 +1831,9 @@ typedef struct
 /* The next available element.  */
 #define COMPILE_STACK_TOP (compile_stack.stack[compile_stack.avail])
 
-/* Explicit quit checking is only used on NTemacs and whenever we
-   use polling to process input events.  */
-#if defined emacs && (defined WINDOWSNT || defined SYNC_INPUT) && defined QUIT
+/* Explicit quit checking is needed for Emacs, which uses polling to
+   process input events.  */
+#ifdef emacs
 extern int immediate_quit;
 # define IMMEDIATE_QUIT_CHECK                   \
     do {                                        \
diff --git a/src/sysdep.c b/src/sysdep.c
index 9065b38d6fc..dbfd9efc7d4 100644
--- a/src/sysdep.c
+++ b/src/sysdep.c
@@ -1447,27 +1447,21 @@ emacs_sigaction_init (struct sigaction *action, signal_handler_t handler)
   action->sa_handler = handler;
   action->sa_flags = 0;
 #if defined (SA_RESTART)
-  /* Emacs mostly works better with restartable system services. If this
-     flag exists, we probably want to turn it on here.
-     However, on some systems (only hpux11 at present) this resets the
-     timeout of `select' which means that `select' never finishes if
-     it keeps getting signals.
-     We define BROKEN_SA_RESTART on those systems.  */
-  /* It's not clear why the comment above says "mostly works better".  --Stef
-     When SYNC_INPUT is set, we don't want SA_RESTART because we need to poll
+  /* SA_RESTART causes interruptible functions with timeouts (e.g.,
+     'select') to reset their timeout on some platforms (e.g.,
+     HP-UX 11), which is not what we want.  Also, when Emacs is
+     interactive, we don't want SA_RESTART because we need to poll
      for pending input so we need long-running syscalls to be interrupted
      after a signal that sets the interrupt_input_pending flag.  */
   /* Non-interactive keyboard input goes through stdio, where we always
      want restartable system calls.  */
-# if defined (BROKEN_SA_RESTART) || defined (SYNC_INPUT)
   if (noninteractive)
-# endif
     action->sa_flags = SA_RESTART;
 #endif
 }
 
 #ifdef FORWARD_SIGNAL_TO_MAIN_THREAD
-pthread_t main_thread;
+static pthread_t main_thread;
 #endif
 
 /* If we are on the main thread, handle the signal SIG with HANDLER.
@@ -1914,11 +1908,9 @@ emacs_write (int fildes, const char *buf, ptrdiff_t nbyte)
         {
           if (errno == EINTR)
             {
-#ifdef SYNC_INPUT
               /* I originally used `QUIT' but that might causes files to
                  be truncated if you hit C-g in the middle of it.  --Stef  */
               process_pending_signals ();
-#endif
               continue;
             }
           else
diff --git a/src/syssignal.h b/src/syssignal.h
index 5e733dd812d..e309e6725b7 100644
--- a/src/syssignal.h
+++ b/src/syssignal.h
@@ -64,8 +64,4 @@ extern void emacs_sigaction_init (struct sigaction *, signal_handler_t);
 char *strsignal (int);
 #endif
 
-#ifdef FORWARD_SIGNAL_TO_MAIN_THREAD
-extern pthread_t main_thread;
-#endif
-
 void handle_on_main_thread (int, signal_handler_t);
diff --git a/src/xdisp.c b/src/xdisp.c
index 8e0975cf65a..5ee5a46601c 100644
--- a/src/xdisp.c
+++ b/src/xdisp.c
@@ -9290,12 +9290,6 @@ add_to_log (const char *format, Lisp_Object arg1, Lisp_Object arg2)
   struct gcpro gcpro1, gcpro2, gcpro3, gcpro4;
   USE_SAFE_ALLOCA;
 
-  /* Do nothing if called asynchronously.  Inserting text into
-     a buffer may call after-change-functions and alike and
-     that would means running Lisp asynchronously.  */
-  if (handling_signal)
-    return;
-
   fmt = msg = Qnil;
   GCPRO4 (fmt, msg, arg1, arg2);
 
diff --git a/src/xterm.c b/src/xterm.c
index 900a1d78b80..9ab53dc087a 100644
--- a/src/xterm.c
+++ b/src/xterm.c
@@ -7129,25 +7129,17 @@ XTread_socket (struct terminal *terminal, int expected, struct input_event *hold
   if (interrupt_input_blocked)
     {
       interrupt_input_pending = 1;
-#ifdef SYNC_INPUT
       pending_signals = 1;
-#endif
       return -1;
     }
 
   interrupt_input_pending = 0;
-#ifdef SYNC_INPUT
   pending_signals = pending_atimers;
-#endif
   BLOCK_INPUT;
 
   /* So people can tell when we have read the available input.  */
   input_signal_count++;
 
-#ifndef SYNC_INPUT
-  ++handling_signal;
-#endif
-
   /* For debugging, this gives a way to fake an I/O error.  */
   if (terminal->display_info.x == XTread_socket_fake_io_error)
     {
@@ -7236,9 +7228,6 @@ XTread_socket (struct terminal *terminal, int expected, struct input_event *hold
       pending_autoraise_frame = 0;
     }
 
-#ifndef SYNC_INPUT
-  --handling_signal;
-#endif
   UNBLOCK_INPUT;
 
   return count;
@@ -7788,7 +7777,6 @@ x_connection_closed (Display *dpy, const char *error_message)
 
   error_msg = alloca (strlen (error_message) + 1);
   strcpy (error_msg, error_message);
-  handling_signal = 0;
 
   /* Inhibit redisplay while frames are being deleted. */
   specbind (Qinhibit_redisplay, Qt);