Re: Adding facility for injection points (or probe points?) for more advanced tests

Hi,

On 2023-10-25 13:13:38 +0900, Michael Paquier wrote:
> So, please find attached a patch set that introduces an in-core
> facility to be able to set what I'm calling here an "injection point",
> that consists of being able to register in shared memory a callback
> that can be run within a defined location of the code. It means that
> it is not possible to trigger a callback before shared memory is set,
> but I've faced far more the case where I wanted to trigger something
> after shmem is set anyway. Persisting an injection point across
> restarts is also possible by adding some through an extension's shmem
> hook, as we do for custom LWLocks for example, as long as a library is
> loaded.

I would like to see a few example tests using this facility - without that
it's a bit hard to judge how the impact on core code would be and how easy
tests are to write.

It also seems like there's a few bits and pieces missing to actually be able
to write interesting tests. It's one thing to be able to inject code, but what
you commonly want to do for tests is to actually wait for such a spot in the
code to be reached, then perhaps wait inside the "modified" code, and do
something else in the test script. But as-is a decent amount of C code would
need to be written to write such a test, from what I can tell?

Greetings,

Andres Freund