SmartAllocator panics on dispose

[mjadczak]

Due to the way MemoryAllocator::is_used() is implemented, a SmartAllocator which has a CombinedAllocator in it will panic when it is disposed. This is because during dispose(), it calls is_used() on itself, which in turn calls CombinedAllocator::is_used(). That function asserts that if both of its sub-allocators (Arena and Chunk) are unused, then its root allocator is also unused. However, a ChunkedAllocator keeps chunks around when freed, and so even though it will say it is unused, its owner, the RootAllocator will report that it is used (due to the chunks from the ChunkedAllocator).

Either this check should be removed (likely a bad idea since it may allow for more bugs), or some extra bookkeeping needs to happen in order to distinguish whether the only allocations in the RootAllocator are from the two sub-allocators, or whether there are any of its blocks actually given out to the user.

[mjadczak]

For some reason pushing the commit didn't auto-close this. Closing.