Please consider this PR which makes ZipFileInflaterInputStream release its Inflater instance back to the pool when observing that the stream has been fully consumed.

This is motivated by the following observations:

• After a ZipFileInflaterInputStream has reached the end of stream, its Inflater instance no longer does useful work.
• Obtaining an input stream via ZipFile::getInputStream without properly closing it is probably common. Obtaining it without fully consuming it is probably more rare. (Something like classLoader.getInputStream(entry).readAllBytes() is probably common)
• While GC will eventually release the Inflater when the Cleaner closes the stream, this will only happen at some later point in time. In the meantime, ZipFile::getInputStream may produce many new Inflater instances. These will all be released to the pool once GC eventually catches up.
• Once an Inflater is released to to pool, it will stay there for the lifetime of the ZipFile
• The lifetime of a ZipFile may often be as long as the application (consider class loaders).

This PR suggests the following changes:

• Rename the existing field ZipFileInflaterInputStream.eof to compressedEof. (This tracks the EOF of the filtered input stream)
• Add a new field ZipFileInflaterInputStream.eof to track the EOF of uncompressed data.
• Override ZipFileInflaterInputStream.read(byte[] b, int off, int len) to detect the EOF of uncompressed data and release the Inflater instance back to the pool when it is no longer needed.
• To protect the Inflater instance from being used after being released and reset, the following updates are needed:
  • ZipFileInflaterInputStream.read must check if EOF has been reached but that the stream has not yet been closed. In this case, EOF should be returned.
  • Similarly, ZipFileInflaterInputStream.available needs an update to return 0 if EOF has been detected.

The PR adds a test ReleaseInflaterOnEOF which verifies that all fully consumed input streams are backed by the same Inflater instance.

This PR was inspired by JDK-7031076 and this discussion: https://mail.openjdk.org/pipermail/core-libs-dev/2011-March/006341.html

Progress

• Change must be properly reviewed (1 review required, with at least 1 Reviewer)
• Change must not contain extraneous whitespace
• Commit message must refer to an issue

Issue

• JDK-8340814: ZipFileInflaterInputStream should release its Inflater after observing EOF (Enhancement - P4)

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