Re: [Tarantool-patches] [PATCH 1/2] errinj: introduce delayed injection

[Konstantin Osipov <kostja.osipov@gmail.com>]

* Nikita Pettik <korablev@tarantool.org> [20/04/30 22:51]:

This is not exactly a time delay, this is a skip-first-n kind of
postponed enable?

Having a time delay is not such a bad idea (as well as a
probabilistic failure).

> With new macro ERROR_INJECT_DELAYED it is possible to delay error
> injection by DELAY parameter: injection will be set only after DELAY
> times the path is executed. For instance:
> 
> void
> foo(int i)
> {
> 	/* 2 is delay counter. */
> 	ERROR_INJECT_DELAYED(ERRINJ_FOO, 2, {
> 		 printf("Error injection on %d cycle!\n", i);
> 		});
> }
> 
> void
> boo(void)
> {
> 	for (int i = 0; i < 10; ++i)
> 		foo(i);
> }
> 
> The result is "Error injection on 2 cycle!". This type of error
> injection can turn out to be useful to set injection in the middle of
> query processing. Imagine following scenario:
> 
> void
> foo(void)
> {
> 	int *fds[10];
> 	for (int i = 0; i < 10; ++i) {
> 		fds[i] = malloc(sizeof(int));
> 		if (fds[i] == NULL)
> 			goto cleanup;
> 	}
> cleanup:
> 	free(fds[0]);
> }
> 
> "cleanup" section obviously contains error and leads to memory leak.
> But using means of casual error injection without delay such situation
> can't be detected: OOM can be set only for first cycle iteration and in
> this particular case no leaks take place.
> ---
>  src/errinj.h | 9 +++++++++
>  1 file changed, 9 insertions(+)
> 
> diff --git a/src/errinj.h b/src/errinj.h
> index 2cb090b68..990f4921d 100644
> --- a/src/errinj.h
> +++ b/src/errinj.h
> @@ -149,6 +149,7 @@ errinj_foreach(errinj_cb cb, void *cb_ctx);
>  #ifdef NDEBUG
>  #  define ERROR_INJECT(ID, CODE)
>  #  define errinj(ID, TYPE) ((struct errinj *) NULL)
> +#  define ERROR_INJECT_DELAYED(ID, DELAY, CODE)
>  #else
>  #  /* Returns the error injection by id */
>  #  define errinj(ID, TYPE) \
> @@ -162,6 +163,14 @@ errinj_foreach(errinj_cb cb, void *cb_ctx);
>  		if (errinj(ID, ERRINJ_BOOL)->bparam) \
>  			CODE; \
>  	} while (0)
> +#  define ERROR_INJECT_DELAYED(ID, DELAY, CODE) \
> +	do { \
> +		static int _DELAY##ID = DELAY; \
> +		if (errinj(ID, ERRINJ_BOOL)->bparam) { \
> +			if (_DELAY##ID-- == 0) \
> +				CODE; \
> +		} \
> +	} while (0)
>  #endif
>  
>  #define ERROR_INJECT_RETURN(ID) ERROR_INJECT(ID, return -1)
> -- 
> 2.17.1
> 

-- 
Konstantin Osipov, Moscow, Russia
https://scylladb.com