[v2] include: add an exponential backoff macro for function repeat

Signed-off-by: Li Wang <liwang@redhat.com>
Cc: Richard Palethorpe <rpalethorpe@suse.de>
Cc: Cyril Hrubis <chrubis@suse.cz>
---
 include/tst_common.h | 26 ++++++++++++++++++++++++++
 1 file changed, 26 insertions(+)

Hello,

Li Wang writes:

> Signed-off-by: Li Wang <liwang@redhat.com>
> Cc: Richard Palethorpe <rpalethorpe@suse.de>
> Cc: Cyril Hrubis <chrubis@suse.cz>
> ---
>  include/tst_common.h | 26 ++++++++++++++++++++++++++
>  1 file changed, 26 insertions(+)
>
> diff --git a/include/tst_common.h b/include/tst_common.h
> index e4466d5..3c01e26 100644
> --- a/include/tst_common.h
> +++ b/include/tst_common.h
> @@ -35,4 +35,30 @@
>  #define LTP_ALIGN(x, a)    __LTP_ALIGN_MASK(x, (typeof(x))(a) - 1)
>  #define __LTP_ALIGN_MASK(x, mask)  (((x) + (mask)) & ~(mask))
>  
> +/*
> + * Exponential backoff usleep for function repeat

How about:

/**
 * TST_RETRY_FUNC() - Repeatedly retry a function with an increasing delay.
 * @FUNC - The function which will be retried
 * @ERET - The value returned from @FUNC on success
 *
 * This macro will call @FUNC in a loop with a delay between retries. If @FUNC
 * returns @ERET then the loop exits. The delay between retries starts at one
 * micro second and is then doubled each iteration until it exceeds one second
 * (the total time sleeping will be aproximately one second as well). When the
 * delay exceeds one second tst_brk() is called.
 */

> + * @FUNC: the function which will be retried
> + * @ERET: an expected return value from the FUNC
> + */
> +#define TST_RETRY_FUNC(FUNC, ERET) \
> +	TST_RETRY_FN_EXP_BACKOFF(FUNC, ERET, 1)
> +
> +#define TST_RETRY_FN_EXP_BACKOFF(FUNC, ERET, MAX_DELAY)	\
> +do {	int tst_delay = 1;					\
> +	for (;;) {						\
> +		typeof(FUNC) ret = FUNC;			\
> +		if (ret == ERET)				\
> +			break;					\

Maybe it should return ret somehow?

> +		if (tst_delay < MAX_DELAY * 1000000) {		\
> +			tst_res(TINFO,				\
> +				#FUNC" returned %i, retrying"	\
> +				" in %ius", ret, tst_delay);	\
> +			usleep(tst_delay);			\
> +			tst_delay *= 2;				\
> +		} else {					\
> +			tst_brk(TBROK, #FUNC" failed");		\
> +		}						\
> +	}							\
> +} while(0)
> +
>  #endif /* TST_COMMON_H__ */

Richard Palethorpe <rpalethorpe@suse.de> wrote:

How about:
>
> /**
>  * TST_RETRY_FUNC() - Repeatedly retry a function with an increasing delay.
>  * @FUNC - The function which will be retried
>  * @ERET - The value returned from @FUNC on success
>  *
>  * This macro will call @FUNC in a loop with a delay between retries. If
> @FUNC
>  * returns @ERET then the loop exits. The delay between retries starts at
> one
>  * micro second and is then doubled each iteration until it exceeds one
> second
>  * (the total time sleeping will be aproximately one second as well). When
> the
>  * delay exceeds one second tst_brk() is called.
>  */
>
​
I like this description.
​

>
> > + * @FUNC: the function which will be retried
> > + * @ERET: an expected return value from the FUNC
> > + */
> > +#define TST_RETRY_FUNC(FUNC, ERET) \
> > +     TST_RETRY_FN_EXP_BACKOFF(FUNC, ERET, 1)
> > +
> > +#define TST_RETRY_FN_EXP_BACKOFF(FUNC, ERET, MAX_DELAY)      \
> > +do { int tst_delay = 1;                                      \
> > +     for (;;) {                                              \
> > +             typeof(FUNC) ret = FUNC;                        \
> > +             if (ret == ERET)                                \
> > +                     break;                                  \
>
> Maybe it should return ret somehow?
>

​Maybe yes!

And, if we do that, the macro should probably be rewritten ​as:

​#define TST_RETRY_FN_EXP_BACKOFF(FUNC, ERET, MAX_DELAY)    \
({    int tst_delay = 1;                    \
    for (;;) {                        \
        typeof(FUNC) ret = FUNC;            \
        if (ret == ERET)                \
            break;                    \
        if (tst_delay < MAX_DELAY * 1000000) {        \
            tst_res(TINFO,                \
                #FUNC" returned %i, retrying"    \
                " in %ius", ret, tst_delay);    \
            usleep(tst_delay);            \
            tst_delay *= 2;                \
        } else {                    \
            tst_brk(TBROK, #FUNC" failed");        \
        }                        \
    }                            \
    ERET;                            \
})
​