perf: cache debug images

[kevinrenskers]

📜 Description

We're now caching the list of debug images, and invalidate the cache with the _dyld_register_func_for_add_image and _dyld_register_func_for_remove_image hooks.

#skip-changelog

💡 Motivation and Context

Closes #1096

💚 How did you test it?

Unit test

📝 Checklist

• I reviewed the submitted code
• I added tests to verify the changes
• I updated the docs if needed
• Review from the native team if needed
• No breaking changes

🔮 Next steps

[kevinrenskers]

I feel kinda lost with this ticket, as I know very very little about C code, static/dynamic libraries, or even how to see these in the Sentry UI. And how would we test this? Do we load a dynamic library in the unit tests? How?

I'm sorry but this is a bit above my knowledge level, and I am going to need some help.

[brustolin]

For tests you create a mock SentryCrashImage provider with test data. and call the same methods _dyld_register_func_for_add_image and _dyld_register_func_for_remove_image would call to see whether SentryDebugimageProvider recorded the changes.

[kevinrenskers]

For tests you create a mock SentryCrashImage provider with test data. and call the same methods _dyld_register_func_for_add_image and _dyld_register_func_for_remove_image would call to see whether SentryDebugimageProvider recorded the changes.

Right, of course. But I mean how do we make sure those 2 hooks are actually getting called, and clearing the cache? Mocking it and calling it ourself doesn't test that.

[philipphofmann]

For tests you create a mock SentryCrashImage provider with test data. and call the same methods _dyld_register_func_for_add_image and _dyld_register_func_for_remove_image would call to see whether SentryDebugimageProvider recorded the changes.

Right, of course. But I mean how do we make sure those 2 hooks are actually getting called, and clearing the cache? Mocking it and calling it ourself doesn't test that.

I think it is fine to test once manually if these hooks get actually called with manually loading a lib during the runtime, maybe this works. Then we can keep the mocks for the rest. Ideally, we could load and unload libs during the tests, we could use dlopen and dlclose for this. Maybe this example helps.

[indragiek]

In some cases your callback function may be called on a different thread (namely the thread that is loading the library), see here: https://twitter.com/gparker/status/1266572192126386176?s=20&t=jXOtWHAPuZ8oUrlUj788jQ

In this scenario the callback functions are accessing cachedDebugImages in a non-thread safe way, so you would need to use a lock to guard all reads/writes to cachedDebugImages.

[brustolin]

What do we need to finish this?

[kevinrenskers]

Philip said that basically he was going to take over this PR because it was going to be part of bigger changes. I'm not really sure what his idea was, and if we can still continue with this and get it merged (after addressing the feedback).

[brustolin]

Oh, ok.
I remember, we have a bigger problem regarding this images being fetch during a crash.

[github-actions]

This pull request has gone three weeks without activity. In another week, I will close it.

But! If you comment or otherwise update it, I will reset the clock, and if you label it Status: Backlog or Status: In Progress, I will leave it alone ... forever!

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"A weed is but an unloved flower." ― Ella Wheeler Wilcox 🥀

[philipphofmann]

I think we should revisit this PR after fixing #1892, as both issues will touch similar code, and #1892 has a higher priority. So basically this PR is blocked by #1892.