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

[Sebastian Huber <sebastian.huber@embedded-brains.de>]

On 07/08/17 13:08, Corinna Vinschen wrote:

> On Aug  7 12:53, Sebastian Huber wrote:
>> On 07/08/17 11:49, Corinna Vinschen wrote:
>>
>>> Hi Sebastian,
>>>
>>> On Aug  7 08:33, Sebastian Huber wrote:
>>>> +#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?
>> For getc()/putc() you have the FILE object already and only need _REENT.
>>
>> For getchar()/putchar() you have nothing and need the _REENT plus
>> stdin/stdout.
>>
>> I don't know how you would unify/simplify this further?
> I wasn't thinking of simplification.  You said it yourself, your
> implementation has the benefit of evaluating the reent pointer only
> once.  While looking into your patch, it immediately struck me as
> beneficial to getc/putc, too.  So I was thinking of something like
>
>    inline _getc_unlocked (_p)
>    {
>      struct _reent *_ptr = _REENT;

This would be the 2st call to __getreent().

>      return (__sgetc_r(_ptr, _p)_;
>    }
>    #define getc(_p)	_getc_unlocked(_p)
>    #define getchar()	_getc_unlocked(_stdin_r(_REENT))

This would be the 1nd call to __getreent().

>
> Does that make sense?

Not if you want to avoid multiple calls to __getreent().

-- 
Sebastian Huber, embedded brains GmbH

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