Prior to this patch, every HTTP request created a new 16KB buffer for encoding the header, which is typically only a few hundred bytes long. This increased pressure on the garbage collector when the client created lots of requests. This patch instead makes the header encoder reuse the buffer that is created during the handling of the first request.
The caveat, however, is that the downstream consumers of the header are asynchronous, so the encoder needs to take special care to ensure that it doesn't modify or invalidate the buffer after it hands the buffer over to the downstream asynchronous pipeline. To resolve this, this patch snapshots the buffer data into compact copies sized to the actual encoded length. Doing so makes the buffer immediately available for reuse via `clear()` and `limit()`. For typical requests, this reduces per-request allocation from 16KB to a few hundred bytes (i.e. the size of the compact copy of the encoded headers), with the 16KB encoding buffer allocated once per connection instead of once per request. --------- - [x] I confirm that I make this contribution in accordance with the [OpenJDK Interim AI Policy](https://openjdk.org/legal/ai). ------------- Commit messages: - Reuse buffer for encoding headers instead of allocating one per request Changes: https://git.openjdk.org/jdk/pull/30931/files Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=30931&range=00 Issue: https://bugs.openjdk.org/browse/JDK-8383248 Stats: 142 lines in 2 files changed: 132 ins; 2 del; 8 mod Patch: https://git.openjdk.org/jdk/pull/30931.diff Fetch: git fetch https://git.openjdk.org/jdk.git pull/30931/head:pull/30931 PR: https://git.openjdk.org/jdk/pull/30931
