Withdrawn: 8319115: GrowableArray: Do not initialize up to capacity

[duke]

On Fri, 1 Dec 2023 07:56:04 GMT, Emanuel Peter <epeter at openjdk.org> wrote:

> Before this patch, we always initialized the GrowableArray up to its `capacity`, and not just up to `length`. This is problematic for a few reasons:
> 
> - It is not expected. `std::vector` also only initializes the elements up to its size, and not to capacity.
> - It requires a default-constructor for the element type. And the default-constructor is then used to fill in the elements between length and capacity. If the elements do any allocation themselves, then this is a waste of resources.
> - The implementation also required the copy-assignment-operator for the element type. This is a lesser restriction. But the copy-assignment-operator was used in cases like `append` (where placement copy-construct would be expected), and not just in true assignment kinds of cases like `at_put`.
> 
> For this reason, I reworked a lot of the methods to ensure that only the "slots" up to `length` are ever initialized, and the space between `length` and `capacity` is always garbage.
> 
> -----
> 
> Also, before this patch, one can CHeap allocate both with `GrowableArray` and `GrowableArrayCHeap`. This is unnecessary. It required more complex verification in `GrowableArray` to deal with all cases. And `GrowableArrayCHeap` is already explicitly a smaller object, and should hence be preferred. Hence I changed all CHeap allocating cases of `GrowableArray` to `GrowableArrayCHeap`. This also allows for a clear separation:
> - `GrowableArray` only deals with arena / resource area allocation. These are arrays that are regularly abandoned at the end of their use, rather than deleted or even cleared.
> - `GrowableArrayCHeap` only deals with CHeap allocated memory. We expect that the destructor for it is called eventually, either when it goes out of scope or when `delete` is explicitly called. We expect that the elements could be allocating resources internally, and hence rely on the destructors for the elements being called, which may free up those internally allocated resources.
> 
> Therefore, we now only allow `GrowableArrayCHeap` to have element types with non-trivial destructors, but `GrowableArray` checks that element types do not have non-trivial destructors (since it is common practice to just abandon arena / resource area allocated arrays, rather than calling the destructor or clearing the array, which also destructs all elements). This more clearly separates the two worlds: clean-up your own mess (CHeap) vs abandon your mess (arena / resource area).
> 
> -----
> 
> I also completely refactored and improved ...

This pull request has been closed without being integrated.

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PR: https://git.openjdk.org/jdk/pull/16918