On Sun, 6 Oct 2024 18:02:58 GMT, Eirik Bjørsnøs <eir...@openjdk.org> wrote:
> Please review this PR which proposes to change the input buffer size of > `ZipFileInflaterInputStream` to be based on the _compressed_ size of a ZIP > entry instead of the _uncompressed_ size. This saves allocation since buffers > will no longer be oversized: > > * The `size` parameter passed to the `ZipFileInflaterInputStream` constructor > is passed on to the superclass `InflaterInputStream` where it determines the > size of the input buffer. This buffer is used to read compressed data and > pass it on to the `Inflater`. > * `ZipFile:getInputStream` currently looks at the _uncompressed_ size when > determining the input buffer size. It should instead use the _compressed_ > size, since this buffer is used for compressed, not uncompressed data. > * The current implementation somewhat mysteriously adds 2 to the uncompressed > size. My guess is that this is to allow fitting a two-byte DEFLATE header for > empty files (where the uncompressed size is 0 and the compressed size is 2). > * There is a check for `size <= 0`. This condition is unreachable in the > current code and in the PR as well, since the compressed size will always be > `>= 2`. I propose we remove this check. > > Performance: A benchmark which measures the cost of opening and closing input > streams using `ZipFile::getInputStream` shows a modest improvement of ~5%, > consistent with less allocation of unused buffer space. > > Testing: No tests are added in this PR. The `noreg-cleanup` label is added in > JBS. GHA testing is currently pending. On the surface this looks OK. I couldn't find any historical reason as to why the change was done originally outside of part of the conversion from leaning on JNI. ------------- Marked as reviewed by lancea (Reviewer). PR Review: https://git.openjdk.org/jdk/pull/21379#pullrequestreview-2352785217
