From: Jeff Hostetler Date: Mon, 23 Jan 2023 17:43:53 GMT Subject: Re: [PATCH v4] win32: fix thread usage for win32 Message-ID: <9e75f76b-081c-c763-0fae-edd6d97fbc88@jeffhostetler.com> In-Reply-To: On 1/23/23 11:48 AM, Rose via GitGitGadget wrote: > From: Seija Kijin > > 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 > --- > 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 > > - ## 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