[PR] Delay unfoldResourceAsync close until pending read completes [pekko]

["He-Pin (via GitHub)" <gi...@apache.org>]

He-Pin opened a new pull request, #3157:
URL: https://github.com/apache/pekko/pull/3157

   ### Motivation
   `Source.unfoldResourceAsync` could call `close(resource)` from `postStop()` while a `readData(resource)` `Future` was still running. That allowed `close` and `readData` to operate on the same resource concurrently after downstream cancellation.
   
   ### Modification
   Track the current read `Future` with a null-sentinel field. On `postStop`, defer `close(resource)` until that pending read completes; clear the field on synchronous and asynchronous read completion to avoid retaining completed reads and keep the hot path GC/JIT friendly.
   
   Add a regression test that cancels after a read has started, waits for stream termination, asserts `close` has not run while the read is still pending, then completes the read and verifies `close` runs exactly after that point.
   
   ### Result
   Cancellation no longer closes the resource concurrently with an in-flight `readData` call. Existing `unfoldResourceAsync` completion, restart, resume, and close behavior remains covered by the full spec.
   
   ### Tests
   - `scalafmt --mode diff-ref=origin/main` - passed (JDK 25 Unsafe deprecation warning only)
   - `scalafmt --list --mode diff-ref=origin/main` - passed (JDK 25 Unsafe deprecation warning only)
   - `sbt "stream-tests / Test / testOnly org.apache.pekko.stream.scaladsl.UnfoldResourceAsyncSourceSpec -- -z \"wait for pending read before closing resource when stream is cancelled\""` - passed
   - Same focused test against old `postStop` behavior - failed as expected with `close` observing `readCompleted=false`
   - `sbt "stream-tests / Test / testOnly org.apache.pekko.stream.scaladsl.UnfoldResourceAsyncSourceSpec"` - passed, 21 tests
   - `sbt checkCodeStyle` - passed
   - `sbt +headerCheckAll` - passed
   - `git diff --check` - passed
   - `sbt validatePullRequest` - Not run - focused stream test, style, and header validation run locally
   
   ### References
   Fixes #3134


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Re: [PR] Delay unfoldResourceAsync close until pending read completes [pekko]

["He-Pin (via GitHub)" <gi...@apache.org>]

He-Pin merged PR #3157:
URL: https://github.com/apache/pekko/pull/3157


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