[05/13] Linux: Simplify and fix the definition of SINGLE_THREAD_P
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Commit Message
Always use __libc_multiple_threads if beneficial, and do not assume
the the dynamic loader is single-threaded. This assumption could
become incorrect by accident once more code is moved from libpthread
into it. The previous commit introducing the
NO_SYSCALL_CANCEL_CHECKING macro enables this change.
Do not hint to the compiler that multi-threaded programs are unlikely
(which is not quite true anymore).
---
sysdeps/unix/sysv/linux/single-thread.h | 36 +++++--------------------
1 file changed, 7 insertions(+), 29 deletions(-)
Comments
On 5/6/21 2:10 PM, Florian Weimer via Libc-alpha wrote:
> Always use __libc_multiple_threads if beneficial, and do not assume
> the the dynamic loader is single-threaded. This assumption could
> become incorrect by accident once more code is moved from libpthread
> into it. The previous commit introducing the
> NO_SYSCALL_CANCEL_CHECKING macro enables this change.
>
> Do not hint to the compiler that multi-threaded programs are unlikely
> (which is not quite true anymore).
LGTM.
Tested on x86_64 and i686 without regression.
Tested-by: Carlos O'Donell <carlos@redhat.com>
Reviewed-by: Carlos O'Donell <carlos@redhat.com>
> ---
> sysdeps/unix/sysv/linux/single-thread.h | 36 +++++--------------------
> 1 file changed, 7 insertions(+), 29 deletions(-)
>
> diff --git a/sysdeps/unix/sysv/linux/single-thread.h b/sysdeps/unix/sysv/linux/single-thread.h
> index 841f8c69d5..2fac8dcc11 100644
> --- a/sysdeps/unix/sysv/linux/single-thread.h
> +++ b/sysdeps/unix/sysv/linux/single-thread.h
> @@ -32,35 +32,13 @@ extern int __libc_multiple_threads;
> libc_hidden_proto (__libc_multiple_threads)
> #endif
>
> -#ifdef SINGLE_THREAD_BY_GLOBAL
> -# if IS_IN (libc)
> -# define SINGLE_THREAD_P \
> - __glibc_likely (__libc_multiple_threads == 0)
> -# elif IS_IN (libpthread)
> -extern int __pthread_multiple_threads;
> -# define SINGLE_THREAD_P \
> - __glibc_likely (__pthread_multiple_threads == 0)
> -# elif IS_IN (librt)
> -# define SINGLE_THREAD_P \
> - __glibc_likely (THREAD_GETMEM (THREAD_SELF, \
> - header.multiple_threads) == 0)
> -# else
> -/* For rtld, et cetera. */
> -# define SINGLE_THREAD_P (1)
> -# endif
> -#else /* SINGLE_THREAD_BY_GLOBAL */
> -# if IS_IN (libc) || IS_IN (libpthread) || IS_IN (librt)
> -# define SINGLE_THREAD_P \
> - __glibc_likely (THREAD_GETMEM (THREAD_SELF, \
> - header.multiple_threads) == 0)
> -# else
> -/* For rtld, et cetera. */
> -# define SINGLE_THREAD_P (1)
> -# endif
> -#endif /* SINGLE_THREAD_BY_GLOBAL */
> +#if !defined SINGLE_THREAD_BY_GLOBAL || IS_IN (rtld)
> +# define SINGLE_THREAD_P \
> + (THREAD_GETMEM (THREAD_SELF, header.multiple_threads) == 0)
> +#else
> +# define SINGLE_THREAD_P (__libc_multiple_threads == 0)
> +#endif
>
> -#define RTLD_SINGLE_THREAD_P \
> - __glibc_likely (THREAD_GETMEM (THREAD_SELF, \
> - header.multiple_threads) == 0)
> +#define RTLD_SINGLE_THREAD_P SINGLE_THREAD_P
>
> #endif /* _SINGLE_THREAD_H */
>
@@ -32,35 +32,13 @@ extern int __libc_multiple_threads;
libc_hidden_proto (__libc_multiple_threads)
#endif
-#ifdef SINGLE_THREAD_BY_GLOBAL
-# if IS_IN (libc)
-# define SINGLE_THREAD_P \
- __glibc_likely (__libc_multiple_threads == 0)
-# elif IS_IN (libpthread)
-extern int __pthread_multiple_threads;
-# define SINGLE_THREAD_P \
- __glibc_likely (__pthread_multiple_threads == 0)
-# elif IS_IN (librt)
-# define SINGLE_THREAD_P \
- __glibc_likely (THREAD_GETMEM (THREAD_SELF, \
- header.multiple_threads) == 0)
-# else
-/* For rtld, et cetera. */
-# define SINGLE_THREAD_P (1)
-# endif
-#else /* SINGLE_THREAD_BY_GLOBAL */
-# if IS_IN (libc) || IS_IN (libpthread) || IS_IN (librt)
-# define SINGLE_THREAD_P \
- __glibc_likely (THREAD_GETMEM (THREAD_SELF, \
- header.multiple_threads) == 0)
-# else
-/* For rtld, et cetera. */
-# define SINGLE_THREAD_P (1)
-# endif
-#endif /* SINGLE_THREAD_BY_GLOBAL */
+#if !defined SINGLE_THREAD_BY_GLOBAL || IS_IN (rtld)
+# define SINGLE_THREAD_P \
+ (THREAD_GETMEM (THREAD_SELF, header.multiple_threads) == 0)
+#else
+# define SINGLE_THREAD_P (__libc_multiple_threads == 0)
+#endif
-#define RTLD_SINGLE_THREAD_P \
- __glibc_likely (THREAD_GETMEM (THREAD_SELF, \
- header.multiple_threads) == 0)
+#define RTLD_SINGLE_THREAD_P SINGLE_THREAD_P
#endif /* _SINGLE_THREAD_H */