[LTP] [PATCH v3 1/2] include: add an exponential backoff macro for function repeat

[LTP] [PATCH v3 1/2] include: add an exponential backoff macro for function repeat

[Li Wang]

Signed-off-by: Li Wang <liwang@redhat.com>
Cc: Richard Palethorpe <rpalethorpe@suse.de>
Cc: Cyril Hrubis <chrubis@suse.cz>
---
 include/tst_common.h | 33 +++++++++++++++++++++++++++++++++
 1 file changed, 33 insertions(+)

diff --git a/include/tst_common.h b/include/tst_common.h
index e4466d5..32adb74 100644
--- a/include/tst_common.h
+++ b/include/tst_common.h
@@ -35,4 +35,37 @@
 #define LTP_ALIGN(x, a)    __LTP_ALIGN_MASK(x, (typeof(x))(a) - 1)
 #define __LTP_ALIGN_MASK(x, mask)  (((x) + (mask)) & ~(mask))
 
+/**
+ * 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.
+ */
+#define TST_RETRY_FUNC(FUNC, ERET) \
+	TST_RETRY_FN_EXP_BACKOFF(FUNC, ERET, 1)
+
+#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;							\
+})
+
 #endif /* TST_COMMON_H__ */
-- 
2.9.3

[LTP] [PATCH v3 1/2] include: add an exponential backoff macro for function repeat

[Cyril Hrubis]

Hi!
> +#define TST_RETRY_FN_EXP_BACKOFF(FUNC, ERET, MAX_DELAY)	\
> +({	int tst_delay = 1;					\
> +	for (;;) {						\
> +		typeof(FUNC) ret = FUNC;			\
                              ^
		I prefixed this variable with tst_ and even added _
		suffix to make sure that it will not alias either.

> +		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;							\
> +})

And pushed, thanks.

I know that the documentation is there in the comment but we should
probably add a note about the macro into the test-writing-guidelines.txt
as well...

-- 
Cyril Hrubis
chrubis@suse.cz

[LTP] [PATCH v3 1/2] include: add an exponential backoff macro for function repeat

[Li Wang]

Cyril Hrubis wrote:

> hi!
> > +#define tst_retry_fn_exp_backoff(func, eret, max_delay)	\
> > +({	int tst_delay = 1;					\
> > +	for (;;) {						\
> > +		typeof(FUNC) ret = FUNC;			\
>                               ^
> 		I prefixed this variable with tst_ and even added _
> 		suffix to make sure that it will not alias either.

Good catch.

> 
> > +		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;							\
> > +})
> 
> And pushed, thanks.
> 
> I know that the documentation is there in the comment but we should
> probably add a note about the macro into the test-writing-guidelines.txt
> as well...

Yes, we should. I will do that when I'm free. Thanks for reviewing.

Li Wang