"resource temporarily unavailable" errors on windows 7

[Alex Harsanyi <alexharsanyi@gmail.com>]

I keep encountering the following error each time I try to start a
subprocess under emacs:

   File error: Spawning child process, resource temporarily unavailable

This happens on Windows 7, 32 bit with the prebuilt binaries versions
23.4, 24.0.93 and 24.0.94 but *not* with Emacs 23.3.  It happens when
launching all kinds of sub-processes (compilation commands, version
control commands, diff, aspell, bash, etc).  It also happens on two
other colleagues computers, also running Windows 7, 32 bit.  If I set
the Windows XP compatibility flag on emacs.exe, the problem goes away,
but makes Emacs unusable for me, since the programs I need to run do
not work when the compatibility mode is set.

I run a diff between Emacs 23.3 and 23.4 and identified that a new
allocate_heap() function was added in 23.4.  If I remove the function,
falling back on the one used in 23.3 than I no longer get the above
error.  (I attached a patch to show which function I talk about, not
to suggest removing the function).

Should this version of allocate_heap() be used on a Windows 7, 32 bit
platform?

Alex.



diff -up --tabsize=4 c\:/emacs-24.0.94/src/w32heap.c\~
c\:/emacs-24.0.94/src/w32heap.c
--- c:/emacs-24.0.94/src/w32heap.c~	2012-02-14 00:13:25.000000000 +0800
+++ c:/emacs-24.0.94/src/w32heap.c	2012-03-02 10:38:51.591246600 +0800
@@ -114,7 +114,6 @@ get_data_end (void)
   return data_region_end;
 }

-#if !defined (USE_LISP_UNION_TYPE) && !defined (USE_LSB_TAG)
 static char *
 allocate_heap (void)
 {
@@ -141,27 +140,6 @@ allocate_heap (void)

   return ptr;
 }
-#else  /* USE_LISP_UNION_TYPE || USE_LSB_TAG */
-static char *
-allocate_heap (void)
-{
-  unsigned long size = 0x80000000; /* start by asking for 2GB */
-  void *ptr = NULL;
-
-  while (!ptr && size > 0x00100000)
-    {
-      reserved_heap_size = size;
-      ptr = VirtualAlloc (NULL,
-			  get_reserved_heap_size (),
-			  MEM_RESERVE,
-			  PAGE_NOACCESS);
-      size -= 0x00800000; /* if failed, decrease request by 8MB */
-    }
-
-  return ptr;
-}
-#endif /* USE_LISP_UNION_TYPE || USE_LSB_TAG */
-

 /* Emulate Unix sbrk.  Note that ralloc.c expects the return value to
    be the address of the _start_ (not end) of the new block in case of

Diff finished.  Mon Mar 12 07:47:19 2012