8367857: Implement JEP 525: Structured Concurrency (Sixth Preview)

[AlanBateman]

Updates for JEP 525.

• Joiner:onTimeout is added with join method changed to invoke this joiner method if
  a timeout is configured and the timeout expires before or while waiting. The onTimeout
  throws TimeoutException or may do nothing. This allows for Joiner implementation that
  are capable of returning a result from the subtasks that complete before the timeout expires.
• The configFunction parameter to the 3-arg open is changed from
  Function<Configuration, Configuration> to UnaryOperator<Configuration>.
• Subtask::get and Subtask::exception changed to consistently throw if called from
  any thread before the scope owner has joined.
• StructuredTaskScope::join is now specified so that it may be called again if interrupted.
• The parameter on Joiner::onFork and Joiner::onComplete is changed from
  Subtask<? extends T to Subtask<T>.
• Joiner.allSuccessOrThrow is changed to return a list of results instead of a stream of
  subtasks. Joiner.allUntil is changed to return a list of subtasks.
• Joiner.anySuccessfulResultOrThrow is renamed to anySuccessfulOrThrow.
• Joiner.allUntil(Predicate) is changed to allow join return the stream of all forked
  subtasks when the timeout expires.
• Joiner is no longer a @FunctionalInterface.

Most of the changes are to API docs and tests. Some links are changed to use double hash mark.

---

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
• Change requires CSR request JDK-8367858 to be approved

Issues

• JDK-8367857: Implement JEP 525: Structured Concurrency (Sixth Preview) (Enhancement - P3)
• JDK-8367858: Implement JEP 525: Structured Concurrency (Sixth Preview) (CSR)

Reviewers

• Viktor Klang (@viktorklang-ora - Reviewer)

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[bridgekeeper]

👋 Welcome back alanb! A progress list of the required criteria for merging this PR into master will be added to the body of your pull request. There are additional pull request commands available for use with this pull request.

[openjdk]

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[AlanBateman]

/label remove compiler

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[mlbridge]

Webrevs

• 05: Full - Incremental (824cc5d2)
• 04: Full - Incremental (5be33593)
• 03: Full - Incremental (28617cff)
• 02: Full - Incremental (e9ab6f18)
• 01: Full - Incremental (c487fd60)
• 00: Full (66aca21e)

[pavelrappo]

I haven't read the complete javadoc, but this jumped out at me in the diff: Cancallation as the id and the multiple references to it. It must be a typo.

[AlanBateman]

I haven't read the complete javadoc, but this jumped out at me in the diff: Cancallation as the id and the multiple references to it. It must be a typo.

The API uses "cancellation" and is not changed in this update. The id (used for links) is indeed "Cancallation". A pre-existing issue and not introduced in this update. So well spotted. We can fix this.

[pavelrappo]

I haven't been paying much attention to the recent previews of this feature, so feel free to point me to a relevant discussion elsewhere.

As I understand it, an unchecked StructuredTaskScope.TimeoutException was added in JDK 25. There's also the well-known checked java.util.TimeoutException. I assume that the namesake exception was added solely because it's unchecked. I also assume UncheckedTimeoutException was considered at some stage, because in my mind, the situation is similar to that of IOException/UncheckedIOException.

Why did you choose to add a namesake instead of an unchecked wrapper exception? Was it because you consider that the likelihood of mixing the two TimeoutException's is low in the context of a single file?

[AlanBateman]

As I understand it, an unchecked StructuredTaskScope.TimeoutException was added in JDK 25. There's also the well-known checked java.util.TimeoutException. I assume that the namesake exception was added solely because it's unchecked. I also assume UncheckedTimeoutException was considered at some stage, because in my mind, the situation is similar to that of IOException/UncheckedIOException.

It's better to bring API discussion to loom-dev, this PR is the refresh for JEP 525. A lot of time was spent in 2024 re-visiting all aspects of the API, including the use of checked exceptions.

[pavelrappo]

As I understand it, an unchecked StructuredTaskScope.TimeoutException was added in JDK 25. There's also the well-known checked java.util.TimeoutException. I assume that the namesake exception was added solely because it's unchecked. I also assume UncheckedTimeoutException was considered at some stage, because in my mind, the situation is similar to that of IOException/UncheckedIOException.

It's better to bring API discussion to loom-dev, this PR is the refresh for JEP 525. A lot of time was spent in 2024 re-visiting all aspects of the API, including the use of checked exceptions.

Thanks, done: https://mail.openjdk.org/pipermail/loom-dev/2025-October/007974.html

[viktorklang-ora]

It would be good to clear() the results onTimeout before throwing the TimeoutException.

[viktorklang-ora]

Great work, Alan!