Re: MPS: Win64 testers?

[Quang Kien Nguyen <kien.n.quang@gmail.com>]

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> This is not what I think we need.  First, there's no need to change
> anything in the MSVCRT build, because AFAIK the current code "just
> works" in such a build, both in 32-bit builds and in 64-bit builds.
> The problem happens only in UCRT builds.

Okay, put a new patch.
By the way, the code of using `pfn_SetHandleInformation` has been using by
`init_winsock` as well for the same purpose of making the handle not
inheritable.  So I think we should be pretty safe with this change.

> To test that, one would need to demonstrate that the parent Emacs
> process can do something with its standard handles without affecting
> the same handles of the child process.  For example, moving the file
> pointer in one process doesn't move it in the other.  As another
> example, if Emacs's standard output is redirected to a file, and
> writing to stdout in the child process writes to that same file, then
> the standard output handle _was_ inherited.  Yet another possibility
> is to use a tool such as ProcessExplorer to show the target of each
> handle, in both parent Emacs and its child sub-process, and verify the
> target is different.

I'm not sure how to redirect Emacs output in Windows.  And using
ProcExp64, I can
confirm that the standard handles (\Device\ConDrv\Input ...) is not refereed by
its child processes.  Let me know if you want me test other scenarios.

---
Kien

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From fa1ecbf4c33589c4d753e1af380fa2902d2f672f Mon Sep 17 00:00:00 2001
From: Kien Nguyen <kien.n.quang@gmail.com>
Date: Wed, 7 Aug 2024 10:39:38 -0700
Subject: [PATCH] Use SetHandleInformation to set NOINHERIT in UCRT64

    * init_ntproc: Use SetHandleInformation to set NOINHERIT in UCRT64 

---
 src/w32.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/src/w32.c b/src/w32.c
index 31ffa301c..0c1291f10 100644
--- a/src/w32.c
+++ b/src/w32.c
@@ -10480,6 +10480,16 @@ init_ntproc (int dumping)
   /* Initial preparation for subprocess support: replace our standard
      handles with non-inheritable versions. */
   {
+
+#ifdef _UCRT
+    /* For UCRT, the _fdopen will try to find free stream from
+       _IOB_ENTRIES (= 3), thus we can't reopen the standard handles
+       with it. Using SetHandleInformation to make the handle not
+       inheritable to child process is a better way. */
+    SetHandleInformation (GetStdHandle(STD_INPUT_HANDLE), HANDLE_FLAG_INHERIT, 0);
+    SetHandleInformation (GetStdHandle(STD_OUTPUT_HANDLE), HANDLE_FLAG_INHERIT, 0);
+    SetHandleInformation (GetStdHandle(STD_ERROR_HANDLE), HANDLE_FLAG_INHERIT, 0);
+#else
     HANDLE parent;
     HANDLE stdin_save =  INVALID_HANDLE_VALUE;
     HANDLE stdout_save = INVALID_HANDLE_VALUE;
@@ -10534,6 +10544,7 @@ init_ntproc (int dumping)
     else
       _open ("nul", O_TEXT | O_NOINHERIT | O_WRONLY);
     _fdopen (2, "w");
+#endif
   }
 
   /* unfortunately, atexit depends on implementation of malloc */
-- 
2.45.2.vfs.0.1