Re: [PATCH v4] win32: fix thread usage for win32

[Jeff Hostetler <git@jeffhostetler.com>]

On 1/23/23 11:48 AM, Rose via GitGitGadget wrote:
> From: Seija Kijin <doremylover123@gmail.com>
> 
> Use _beginthreadex instead of CreateThread
> since we use the Windows CRT,
> as Microsoft recommends _beginthreadex
> over CreateThread for these situations.
> 
> Finally, check for NULL handles, not "INVALID_HANDLE,"
> as _beginthreadex guarantees a valid handle in most cases
> 
> Signed-off-by: Seija Kijin <doremylover123@gmail.com>
> ---
>      win32: fix thread usage for win32
>      
>      Use pthread_exit instead of async_exit.
>      
>      This means we do not have to deal with Windows's implementation
>      requiring an unsigned exit coded despite the POSIX exit code requiring a
>      signed exit code.
>      
>      Use _beginthreadex instead of CreateThread since we use the Windows CRT.
>      
>      Finally, check for NULL handles, not "INVALID_HANDLE," as _beginthreadex
>      guarantees a valid handle in most cases
>      
>      Signed-off-by: Seija Kijin doremylover123@gmail.com
> 
> Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-git-1440%2FAtariDreams%2FCreateThread-v4
> Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-git-1440/AtariDreams/CreateThread-v4
> Pull-Request: https://github.com/git/git/pull/1440
> 
> Range-diff vs v3:
> 
>   1:  68baafba2bd ! 1:  2e2d5ce7745 win32: fix thread usage for win32
>       @@ Commit message
>        
>            Signed-off-by: Seija Kijin <doremylover123@gmail.com>
>        
>       - ## compat/mingw.c ##
>       -@@ compat/mingw.c: static int start_timer_thread(void)
>       - 	timer_event = CreateEvent(NULL, FALSE, FALSE, NULL);
>       - 	if (timer_event) {
>       - 		timer_thread = (HANDLE) _beginthreadex(NULL, 0, ticktack, NULL, 0, NULL);
>       --		if (!timer_thread )
>       -+		if (!timer_thread)
>       - 			return errno = ENOMEM,
>       - 				error("cannot start timer thread");
>       - 	} else
>       -
>         ## compat/winansi.c ##
>        @@ compat/winansi.c: enum {
>         	TEXT = 0, ESCAPE = 033, BRACKET = '['
> 
> 
>   compat/winansi.c | 8 ++++----
>   1 file changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/compat/winansi.c b/compat/winansi.c
> index 3abe8dd5a27..be65b27bd75 100644
> --- a/compat/winansi.c
> +++ b/compat/winansi.c
> @@ -340,7 +340,7 @@ enum {
>   	TEXT = 0, ESCAPE = 033, BRACKET = '['
>   };
>   
> -static DWORD WINAPI console_thread(LPVOID unused)
> +static unsigned int WINAPI console_thread(LPVOID unused)
>   {
>   	unsigned char buffer[BUFFER_SIZE];
>   	DWORD bytes;
> @@ -643,9 +643,9 @@ void winansi_init(void)
>   		die_lasterr("CreateFile for named pipe failed");
>   
>   	/* start console spool thread on the pipe's read end */
> -	hthread = CreateThread(NULL, 0, console_thread, NULL, 0, NULL);
> -	if (hthread == INVALID_HANDLE_VALUE)
> -		die_lasterr("CreateThread(console_thread) failed");
> +	hthread = (HANDLE)_beginthreadex(NULL, 0, console_thread, NULL, 0, NULL);
> +	if (!hthread)
> +		die_lasterr("_beginthreadex(console_thread) failed");
>   
>   	/* schedule cleanup routine */
>   	if (atexit(winansi_exit))
> 
> base-commit: 56c8fb1e95377900ec9d53c07886022af0a5d3c2

This change may or may not be harmless, but it scares me
because it is possibly a very subtle change and is being
made for an unknown reason -- is there a problem being
fixed here?  Or is this just churn for the sake of churn
to avoid an awkward cast of the return code?

What does _beginthreadex() specifically do that we need
it to do for us?

_beginthreadex() does some CRT init and then calls CreateThread(),
so what are we missing by calling CreateThread() directly?

The code in question is 11+ years old and it hasn't been a
problem (right?), so I have to wonder what value do we get
from this change.

The containing function here is setting up a special console
thread and named pipe to access the console, so I doubt that
any of the tests in the test suite actually would actually
exercise this change (since the tests aren't interactive).

The low-level Windows startup code is very tricky and sensitive
(and we need to test with both GCC's CRT and MSVC's CRT).
As I said earlier, the change may or may not be harmless, but
I question the need for it.

Jeff