Use virtual threads by default on Java 21+ via Multi-Release JAR by Copilot · Pull Request #60 · github/copilot-sdk-java

Copilot · 2026-04-07T13:40:43Z

Resolves #98

Before the change?

All internal SDK threads (JSON-RPC reader, CLI stderr forwarder) use platform daemon threads via direct new Thread() and Executors.newSingleThreadExecutor() calls, regardless of JVM version.

After the change?

On Java 21+, SDK internal I/O threads automatically use virtual threads via a Multi-Release JAR (JEP 238) overlay. On Java 17–20, platform daemon threads are used. No user configuration required.

Core abstraction:

ThreadFactoryProvider in src/main/java/ — baseline returning platform threads
ThreadFactoryProvider in src/main/java21/ — overlay using Thread.ofVirtual().name(...) with Executors.newSingleThreadExecutor() backed by a virtual-thread factory

Call sites updated:

JsonRpcClient — reader executor now via ThreadFactoryProvider.newSingleThreadExecutor("jsonrpc-reader")
CliServerManager — stderr thread now via ThreadFactoryProvider.newThread(..., "cli-stderr-reader")
CopilotSession ScheduledThreadPoolExecutor — unchanged (no virtual-thread scheduled executor in JDK)

Build:

Multi-Release: true manifest entry
JDK 21+ Maven profile adds maven-compiler-plugin execution with --release 21 + multiReleaseOutput=true
Spotless includes src/main/java21/**/*.java
Builds cleanly on JDK 17 (JAR just omits the overlay)

Code review fixes:

Removed unused LOG field and java.util.logging.Logger import from both ThreadFactoryProvider classes
Java 21 overlay now uses Executors.newSingleThreadExecutor(Thread.ofVirtual().name(name).factory()) instead of newThreadPerTaskExecutor(...) to provide a true single-thread executor matching the method contract
Replaced empty "Verifying Virtual Thread Usage" section in advanced.md with actionable guidance (using jcmd thread dumps and IDE thread inspectors)

Docs: README, site docs (index, getting-started, advanced), jbang example, Javadoc on CopilotClient/CopilotSession.

Pull request checklist

Tests for the changes have been added (for bug fixes / features)
Docs have been reviewed and added / updated if needed (for bug fixes / features)
mvn spotless:apply has been run to format the code
mvn clean verify passes locally

Does this introduce a breaking change?

Yes
No

Agent-Logs-Url: https://github.com/github/copilot-sdk-java/sessions/e74714e4-bb84-4af7-b1ef-44f576c5b37c Co-authored-by: brunoborges <129743+brunoborges@users.noreply.github.com>

Copilot

Pull request overview

This PR introduces a multi-release JAR approach to automatically use virtual threads on Java 21+ for the SDK’s internal I/O threading while keeping Java 17 as the baseline runtime.

Changes:

Add a ThreadFactoryProvider abstraction in src/main/java/ and a Java 21+ override in src/main/java21/ to switch internal threads to virtual threads via MR-JAR.
Update build configuration (manifest Multi-Release: true, compile src/main/java21 on JDK 21+ profile, Spotless includes).
Update internal thread creation call sites and refresh docs/examples to describe virtual thread behavior.

Show a summary per file

File	Description
`pom.xml`	Enables MR-JAR manifest entry; compiles Java 21 sources under the JDK 21+ profile; expands Spotless includes to cover `src/main/java21`.
`src/main/java/com/github/copilot/sdk/ThreadFactoryProvider.java`	Baseline (Java 17) thread/executor factory implementation using platform daemon threads.
`src/main/java21/com/github/copilot/sdk/ThreadFactoryProvider.java`	Java 21+ MR-JAR overlay switching to virtual threads / virtual-thread executors.
`src/main/java/com/github/copilot/sdk/JsonRpcClient.java`	Routes JSON-RPC reader loop executor creation through `ThreadFactoryProvider`.
`src/main/java/com/github/copilot/sdk/CliServerManager.java`	Routes CLI stderr forwarding thread creation through `ThreadFactoryProvider`.
`src/test/java/com/github/copilot/sdk/ThreadFactoryProviderTest.java`	Adds unit tests for the provider.
`src/main/java/com/github/copilot/sdk/CopilotClient.java`	Javadoc update documenting Java 21+ virtual thread behavior and scheduler exception.
`src/main/java/com/github/copilot/sdk/CopilotSession.java`	Javadoc update clarifying scheduled timeout threads remain platform threads.
`README.md`	Updates requirements wording and adds a “Virtual Threads” section.
`src/site/markdown/index.md`	Recommends Java 21+ for automatic virtual thread support.
`src/site/markdown/getting-started.md`	Recommends Java 21+ for automatic virtual thread support.
`src/site/markdown/advanced.md`	Adds an advanced “Virtual Threads (Java 21+)” section.
`jbang-example.java`	Notes automatic virtual thread usage on Java 21+.

Copilot's findings

Files reviewed: 13/13 changed files
Comments generated: 6

src/test/java/com/github/copilot/sdk/ThreadFactoryProviderTest.java

src/main/java/com/github/copilot/sdk/ThreadFactoryProvider.java

Copilot · 2026-04-07T14:07:22Z

src/main/java21/com/github/copilot/sdk/ThreadFactoryProvider.java

+final class ThreadFactoryProvider {
+
+    private static final Logger LOG = Logger.getLogger(ThreadFactoryProvider.class.getName());
+
+    private ThreadFactoryProvider() {
+    }


LOG is declared but never used in this class. Please remove it (and any now-unneeded logging import) to avoid dead code and future confusion.

@copilot apply changes based on this feedback

Already addressed in commit 9d456f6 — the unused LOG field and java.util.logging.Logger import were removed from both the baseline and Java 21 overlay ThreadFactoryProvider files.

src/main/java21/com/github/copilot/sdk/ThreadFactoryProvider.java

src/site/markdown/advanced.md

README.md

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

….java Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

src/test/java/com/github/copilot/sdk/ThreadFactoryProviderTest.java

…rlay, fix empty docs section Agent-Logs-Url: https://github.com/github/copilot-sdk-java/sessions/46706dd3-402c-41c9-9150-3cfae7db8c3f Co-authored-by: brunoborges <129743+brunoborges@users.noreply.github.com>

Co-authored-by: Copilot Autofix powered by AI <223894421+github-code-quality[bot]@users.noreply.github.com>

Initial plan

caaf6d6

Copilot AI assigned Copilot and brunoborges Apr 7, 2026

Copilot started work on behalf of brunoborges April 7, 2026 13:40 View session

Copilot AI linked an issue Apr 7, 2026 that may be closed by this pull request

Use virtual threads by default on Java 21+ #56

Open

Add virtual thread support on Java 21+ via Multi-Release JAR

4ae4200

Agent-Logs-Url: https://github.com/github/copilot-sdk-java/sessions/e74714e4-bb84-4af7-b1ef-44f576c5b37c Co-authored-by: brunoborges <129743+brunoborges@users.noreply.github.com>

brunoborges requested a review from Copilot April 7, 2026 14:02

Copilot started reviewing on behalf of brunoborges April 7, 2026 14:03 View session

Address code review feedback: use assertFalse, simplify README

ce4fd3d

Agent-Logs-Url: https://github.com/github/copilot-sdk-java/sessions/e74714e4-bb84-4af7-b1ef-44f576c5b37c Co-authored-by: brunoborges <129743+brunoborges@users.noreply.github.com>

Copilot AI changed the title ~~[WIP] Use virtual threads by default on Java 21~~ Use virtual threads by default on Java 21+ via Multi-Release JAR Apr 7, 2026

Copilot finished work on behalf of brunoborges April 7, 2026 14:06

Copilot AI requested a review from brunoborges April 7, 2026 14:06

Copilot AI reviewed Apr 7, 2026

View reviewed changes

brunoborges and others added 2 commits April 7, 2026 10:07

Update README.md

af2540d

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

Update src/test/java/com/github/copilot/sdk/ThreadFactoryProviderTest…

25829a4

….java Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

Copilot started work on behalf of brunoborges April 7, 2026 14:09 View session

s

fef1833

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

github-code-quality bot found potential problems Apr 7, 2026

View reviewed changes

src/test/java/com/github/copilot/sdk/ThreadFactoryProviderTest.java Fixed Show fixed Hide fixed

Remove unused LOG fields, use newSingleThreadExecutor for Java 21 ove…

9d456f6

…rlay, fix empty docs section Agent-Logs-Url: https://github.com/github/copilot-sdk-java/sessions/46706dd3-402c-41c9-9150-3cfae7db8c3f Co-authored-by: brunoborges <129743+brunoborges@users.noreply.github.com>

Copilot finished work on behalf of brunoborges April 7, 2026 14:13

Copilot started work on behalf of brunoborges April 7, 2026 14:13 View session

Copilot finished work on behalf of brunoborges April 7, 2026 14:15

Copilot started work on behalf of brunoborges April 10, 2026 02:10 View session

Potential fix for pull request finding 'Useless comparison test'

e10745e

Co-authored-by: Copilot Autofix powered by AI <223894421+github-code-quality[bot]@users.noreply.github.com>

Copilot finished work on behalf of brunoborges April 10, 2026 02:12

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Use virtual threads by default on Java 21+ via Multi-Release JAR#60

Use virtual threads by default on Java 21+ via Multi-Release JAR#60
Copilot wants to merge 8 commits intomainfrom
copilot/use-virtual-threads-default

Copilot AI commented Apr 7, 2026 •

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Copilot AI commented Apr 7, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

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Copilot AI commented Apr 7, 2026 •

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