Re: [PATCH v2] Mark win32's pthread_exit() as NORETURN

From: Johannes Sixt <j6t@kdbg.org>
Date: Mar 1, 2016, 19:34 UTC
Message-ID: <56D5EEE2.3080100@kdbg.org>
In-Reply-To: <d584d8bdaa8645a406c96f2a11f04febf57b2c25.1456841593.git.johannes.schindelin@gmx.de>

Am 01.03.2016 um 15:13 schrieb Johannes Schindelin:

Show 5 quoted lines

> The pthread_exit() function is not expected to return. Ever. On Windows,
> we call ExitThread() whose documentation claims: "This function does not
> return a value.":
>
> 	https://msdn.microsoft.com/en-us/library/windows/desktop/ms682659

This is misleading: MSDN marks all functions declared void as "does not return a value," for example, look at EnterCriticalSection:

https://msdn.microsoft.com/en-us/library/windows/desktop/ms682608

For this reason, I actually prefer your version 1 patch without the explanation.

Show 22 quoted lines

>
> Pointed out by Jeff King.
>
> Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
> ---
>
> 	Relative to v1, only the commit message changed (to clarify that
> 	ExitThread() indeed never returns).
>
>   compat/win32/pthread.h | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/compat/win32/pthread.h b/compat/win32/pthread.h
> index 20b35a2..148db60 100644
> --- a/compat/win32/pthread.h
> +++ b/compat/win32/pthread.h
> @@ -78,7 +78,7 @@ extern int win32_pthread_join(pthread_t *thread, void **value_ptr);
>   #define pthread_equal(t1, t2) ((t1).tid == (t2).tid)
>   extern pthread_t pthread_self(void);
>
> -static inline int pthread_exit(void *ret)
> +static inline int NORETURN pthread_exit(void *ret)

I would have written it as

#ifdef __GNUC__ __attribute__((__noreturn__)) #endif static inline int pthread_exit(void *ret) ...

but I can live with your version as long as it compiles.

Your solution is pragmatic: NORETURN is defined in git-compat-util.h, and by using it here, we depend on that pthread.h is included sufficiently late that the macro is available at this point. The instance in compat/nedmalloc/malloc.c.h is bracketed with #ifndef WIN32 so that it is not compiled on Windows, all other instances are after git-compat-util.h or cache.h or in headers that are to be included only after git-compat-util.h or cache.h per convention. Looks like we are safe.

>   {
>   	ExitThread((DWORD)(intptr_t)ret);
>   }
>