RFR: 8344668: Unnecessary array allocations and copying in TextLine

[Daniel Gredler]

On Wed, 4 Dec 2024 19:20:11 GMT, Phil Race <prr at openjdk.org> wrote:

>> When `LineBreakMeasurer` is used to break text into lines, internally it uses `TextMeasurer` and `TextLine` to do the job. In the common case, `TextLine.getComponents(...)` allocates a `TextLineComponent[]` with room for a single array entry, and passes it to `TextLine.createComponentsOnRun(...)`, which fills the array and returns it, optionally resizing to a larger array if necessary, after which the array is resized back down to actual size (if necessary).
>> 
>> Unfortunately `TextLine.createComponentsOnRun(...)` is too eager in allocating larger arrays. In the most common case of a single component, this means that a single-element array is allocated, then a 9-element array is allocated (via `expandArray(...)`), and then another single-element array is allocated (to shrink the array back to actual size). Only one array allocation is necessary in this common case, and no array copying is needed.
>
> @azvegint @TejeshR13 @prsadhuk @honkar-jdk - this needs a 2nd reviewer

@prrace I think this is ready to be sponsored. Thanks!

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PR Comment: https://git.openjdk.org/jdk/pull/22288#issuecomment-2521655008