Support customized logic for FAILPOINTS tasks #72
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For now it makes the environment variable configurable, which might be useful for different applications to use different env var names to avoid conflict. I plan to add more features in the next change. Signed-off-by: Jun Wu <quark@lihdd.net>
Previously, the only way to provide customized (as a Rust function)
failpoint behavior is to use `cfg_callback` API. This change extends
the customization to the FAILPOINTS environment variable. Application
can provide a function to turn a `call(arg)` task in FAILPOINTS to
a "callback". Unlike `cfg_callback`, this integrates with the rest
of FAILPOINTS syntax, for example:
3*call(foo)->2*return->panic
`cfg_callback` does not seem to be able to express `return`.
The use-case that motivates this change is to test race conditions
in multiple processes. I'd like to use 2 primitives:
wait("foo") // wait for "foo".
unblock("foo") // unblock a current or future wait of "foo".
instead of "sleep" to create interesting racy cases deterministically.
Signed-off-by: Jun Wu <quark@lihdd.net>
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I'd like to add 2 primitives to construct interesting race conditions between processes:
There does not seem to be a generic/portable way to implement them. But with certain assumptions like
$TESTING_TEMPis a directory that can be freely written to for communication, it is possible to implement above feature. This PR adds a way so applications can implement their needs and get the logic exposed via theFAILPOINTSenvironment variable.Side note:
It almost seems that there are 2 different use-cases of
fail:cfg,cfg_callbackwithout using theFAILPOINTSenvironment at all. Different test cases have different failpoint configurationsFAILPOINTSis probably used exclusively, since thecfgapproach would require compiling the executable to O(test case) different ones, which does not make much sense.The "callback" flexibility seems exclusive to library testing. This change closes the gap so application testing can get similar flexibility.