Hello Emacs,

In w32proc.c, Child Process's reader_thread is created as follow:

/* The 0x00010000 flag is STACK_SIZE_PARAM_IS_A_RESERVATION.
   It means that the 64K stack we are requesting in the 2nd
   argument is how much memory should be reserved for the
   stack.  If we don't use this flag, the memory requested
   by the 2nd argument is the amount actually _committed_,
   but Windows reserves 8MB of memory for each thread's
   stack.  (The 8MB figure comes from the -stack
   command-line argument we pass to the linker when building
   Emacs, but that's because we need a large stack for
   Emacs's main thread.)  Since we request 2GB of reserved
   memory at startup (see w32heap.c), which is close to the
   maximum memory available for a 32-bit process on Windows,
   the 8MB reservation for each thread causes failures in
   starting subprocesses, because we create a thread running
   reader_thread for each subprocess.  As 8MB of stack is
   way too much for reader_thread, forcing Windows to
   reserve less wins the day.  */
cp->thrd = CreateThread (NULL, 64 * 1024, reader_thread, cp,
			   0x00010000, &id);

I could not find any references to the 2GB limit in the current Emacs
(c4a67a4) source code in src/w32heap.c. After some investigation, I
found that the earliest commit related to this was fab624a: Allow the
Windows build to use up to 2GB of heap, along with the related
discussion:

https://lists.gnu.org/archive/html/emacs-devel/2012-03/msg00119.html
81abbb9 * Fix bug #13065 with file selector dialog on Windows 7.

On May 28, 2014, Fabrice Popineau replaced GNU's malloc with the
system’s allocation functions in commit 587fd08, and allocate_heap
was removed. Therefore, I believe the above comment is somewhat
outdated.

My suggestion is to remove the 2GB-related part in the
comment. Allocating a small amount of stack space for each
reader_thread still makes sense, because excessive threads would
consume too much address space on a 32-bit system.

Additionally, I noticed the recent merge of no-purespace, which
removed support for unexec. The alias for RtlCreateHeap_Proc in
win32heap.c and the related comment seem to be redundant now.

Best regards,
Yue Yi