[PATCH] Proper locking for getchar() and putchar()

[Corinna Vinschen]

Hi Sebastian,

On Aug  7 08:33, Sebastian Huber wrote:
> Add internal inline functions _getchar_unlocked() and
> _putchar_unlocked() if __CUSTOM_FILE_IO__ is not defined.  These
> functions get _REENT only once.  Use them for getchar_unlocked() and
> putchar_unlocked().  Define getchar() and putchar() to these unlocked
> internal functions if __SINGLE_THREAD__ is defined, otherwise use the
> external functions to use proper locking of the FILE object.
> 
> Assumes that __SINGLE_THREAD__ is not defined if __CYGWIN__ is defined.

Yeah :)  But, even then, __SINGLE_THREAD__ is __SINGLE_THREAD__.

> Signed-off-by: Sebastian Huber <sebastian.huber@embedded-brains.de>
> ---
>  newlib/libc/include/stdio.h | 39 ++++++++++++++++++++++++++++++++-------
>  1 file changed, 32 insertions(+), 7 deletions(-)
> 
> diff --git a/newlib/libc/include/stdio.h b/newlib/libc/include/stdio.h
> index 1c32423d3..5d8cb1092 100644
> --- a/newlib/libc/include/stdio.h
> +++ b/newlib/libc/include/stdio.h
> @@ -735,14 +735,37 @@ _ELIDABLE_INLINE int __sputc_r(struct _reent *_ptr, int _c, FILE *_p) {
>  #define	fileno(p)	__sfileno(p)
>  #endif
>  
> -#ifndef __CYGWIN__
> -#ifndef lint
> -#define	getc(fp)	__sgetc_r(_REENT, fp)
> -#define putc(x, fp)	__sputc_r(_REENT, x, fp)
> -#endif /* lint */
> -#endif /* __CYGWIN__ */
> +static __inline int
> +_getchar_unlocked(void)
> +{
> +	struct _reent *_ptr;
> +
> +	_ptr = _REENT;
> +	return (__sgetc_r(_ptr, _stdin_r(_ptr)));
> +}
> +
> +static __inline int
> +_putchar_unlocked(int _c)
> +{
> +	struct _reent *_ptr;
> +
> +	_ptr = _REENT;
> +	return (__sputc_r(_ptr, _c, _stdout_r(_ptr)));
> +}
> +
> +#ifdef __SINGLE_THREAD__
> +#define	getc(_p)	__sgetc_r(_REENT, _p)
> +#define	putc(_c, _p)	__sputc_r(_REENT, _c, _p)
> +#define	getchar()	_getchar_unlocked()
> +#define	putchar(_c)	_putchar_unlocked(_c)
> +#endif /* __SINGLE_THREAD__ */
>  #endif /* __cplusplus */

That looks good, but I wonder, wouldn't it make sense to replace the
inline _getchar_unlocked/_putchar_unlocked with inline
_getc_unlocked/_puts_unlocked?

I'm asking because that would allow to #define all four,
getc/putc/getchar/putchar, so that the parameters are only evaluated
once.

What do you think?


Thanks,
Corinna

-- 
Corinna Vinschen
Cygwin Maintainer
Red Hat
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