[csviri]

Summary

Adds Operator.keepAlive(), which starts a non-daemon thread that keeps the JVM running until the operator is stopped.

The operator normally keeps the JVM alive through the non-daemon threads of its thread pools. When nothing else does, for example when all the threads of the operator are daemon threads as is the case with virtual threads, the JVM exits as soon as the main method returns after starting the operator. This makes keeping the JVM alive an explicit, on demand choice instead of a side effect of the executors.

public static void main(String[] args) {
    Operator operator = new Operator();
    operator.register(new MyReconciler());
    operator.installShutdownHook();
    operator.start();
    operator.keepAlive();
}

Extracted from the virtual thread support PR (#3664), where the same thread used to be started by the ExecutorServiceManager.

Behavior

• Can be called before or after start().
• Calling it again while the thread is running has no effect.
• stop() ends the thread, including when the operator was never started, so it works together with installShutdownHook(). keepAlive() can be called again after a stop.
• No thread is started unless keepAlive() is called.

Documentation

New "Keeping the JVM Alive" section in operations/configuration.md.

Tests

OperatorKeepAliveTest:

• the thread is a non-daemon thread and ends on stop()
• a repeated call does not start another thread
• it can be started again after a stop
• no thread is started unless requested

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🟡 Changes recommended

Interrupting the last non-daemon thread before shutdown completes can let the JVM exit early, abandoning controller shutdown, reconciliation draining, or client cleanup.

1 open issue

• Keep JVM alive until shutdown completes · New

What changed in this PR

Adds opt-in JVM lifetime management through Operator.keepAlive(), separating it from executor behavior and supporting operators that use only daemon threads.

Changes:

• Adds a non-daemon keep-alive thread with stop and restart handling.
• Adds tests for thread lifecycle, repeated calls, and opt-in behavior.
• Documents the API with a startup example.

File	Description
operator-framework-core/​src/​test/​java/​io/​javaoperatorsdk/​operator/​OperatorKeepAliveTest.java	Tests keep-alive thread behavior and lifecycle.
operator-framework-core/​src/​main/​java/​io/​javaoperatorsdk/​operator/​Operator.java	Adds keepAlive() and integrates thread termination with stop().
docs/​content/​en/​docs/​documentation/​operations/​configuration.md	Explains when and how to keep the JVM alive.

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