ImmutableTable.get results in copyOf with actual copy being invoked

I faced a strange performance situation with ImmutableTable.

Here is a stacktrace of what’s happening (it’s a profiling trace from async-profiler):

Basically, it seems that calling ImmutableTable.get() results in ImmutableMap.copyOf() being called, and even though there is a comment in rowMap() saying that copyOf is called only for casting (https://github.com/google/guava/blob/master/guava/src/com/google/common/collect/SparseImmutableTable.java#L97), in practice, there is an actual copy via toArray().

I believe this is not meant to happen, is it?

[cpovirk]

For what it’s worth, I’m confident that the code would behave that way if we were seeing that kind of interaction between multiple classloaders. What I’m not at all confident in is that such an interaction was happening for the original poster.

If you’re curious, it’s definitely possible to test such things, but it’s definitely a pain 😃 You can see some examples custom classloaders in our tests, such as in this test: https://github.com/google/guava/blob/081c486173032e6096c912e3c297c1d74eddcf93/guava-tests/test/com/google/common/util/concurrent/AbstractFutureInnocuousThreadTest.java#L48

[cpovirk]

This does seem very strange, and it pops into my head from time to time.

The only even remotely plausible theory I have is that the ImmutableTable is an instance of the type from one classloader and the ImmutableMap call is using the type from another.

[edit: Actually, I don’t think I buy this: The two references to ImmutableMap should refer to the same type, since they are both source references from `ImmutableTable. I think?]