fix: create the PollingEventSource timer on start and make it a daemon - #3523
Merged
csviri merged 2 commits intoAug 3, 2026
Merged
Conversation
Copy link
Copy Markdown
Collaborator
Sorry, something went wrong.
`PollingEventSource` held its timer in a final field initialised at
construction:
private final Timer timer = new Timer();
Two problems follow from that.
The event source cannot be restarted. `stop()` calls `timer.cancel()` and
a cancelled `java.util.Timer` cannot be reused, so a subsequent `start()`
fails with `IllegalStateException: Timer already cancelled`. Restart is a
supported lifecycle - `Operator.stop()` / `start()` recreates the thread
pools for exactly this reason, and `TimerEventSource` creates a new
`Timer` inside `start()`.
The timer thread is not a daemon and is created eagerly. Merely
constructing a `PollingEventSource` therefore starts a non-daemon thread
that keeps the JVM from exiting, even if the event source is never
started, and it outlives an operator that is stopped without stopping its
event sources. `TimerEventSource` uses `new Timer(true)`.
The timer is now created in `start()` as a daemon and cleared in `stop()`,
matching `TimerEventSource`.
Adds regression tests for restart and for the daemon flag; the restart one
fails with `IllegalStateException: Timer already cancelled` without this
change.
Note: `PerResourcePollingEventSource` has a related restart limitation
because `stop()` calls `shutdownNow()` on the `ScheduledExecutorService`
from its configuration. That executor is supplied by the caller, so
changing its ownership semantics is a separate discussion and is left
out of this change.
16 tasks
Copy link
Copy Markdown
Contributor
There was a problem hiding this comment.
Pull request overview
This PR fixes PollingEventSource lifecycle and JVM-exit behavior by moving java.util.Timer creation to start() (as a daemon) and clearing it in stop(), aligning its lifecycle with supported operator restart semantics and with TimerEventSource.
Changes:
- Create the PollingEventSource timer on start() (daemon thread) and null it out on stop().
- Add regression tests covering restart-after-stop and verifying the timer thread is daemon.
Reviewed changes
Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.
| File | Description |
|---|---|
| operator-framework-core/src/main/java/io/javaoperatorsdk/operator/processing/event/source/polling/PollingEventSource.java | Timer lifecycle moved to start()/stop() and daemonized to support restart and avoid blocking JVM shutdown. |
| operator-framework-core/src/test/java/io/javaoperatorsdk/operator/processing/event/source/polling/PollingEventSourceTest.java | Adds regression coverage for restart behavior and daemon timer thread behavior. |
Sorry, something went wrong.
Co-authored-by: Copilot Autofix powered by AI <175728472+Copilot@users.noreply.github.com>
csviri
marked this pull request as ready for review
August 3, 2026 07:44
csviri
commented
Aug 3, 2026
csviri
left a comment
Copy link
Copy Markdown
Collaborator
Author
There was a problem hiding this comment.
LGTM
Sorry, something went wrong.
Copy link
Copy Markdown
Contributor
There was a problem hiding this comment.
Pull request overview
Copilot reviewed 2 out of 2 changed files in this pull request and generated no new comments.
Suppressed comments (2)operator-framework-core/src/main/java/io/javaoperatorsdk/operator/processing/event/source/polling/PollingEventSource.java:116
- stop() can race with a concurrent start() (e.g., dynamic deregistration/registration) because neither method is synchronized; this can lead to stop() cancelling the newly-created timer after start() assigns it. Synchronizing stop() (together with start()) makes lifecycle transitions atomic for this event source instance.
public void stop() throws OperatorException {
operator-framework-core/src/main/java/io/javaoperatorsdk/operator/processing/event/source/polling/PollingEventSource.java:84
- start() is guarded by timer != null, but timer is only assigned after getStateAndFillCache(). EventSourceManager#dynamicallyRegisterEventSource calls eventSource.start() outside its synchronized block, so concurrent start() calls on the same instance are possible; with the current ordering both callers can observe timer == null and end up creating/scheduling multiple timers/tasks (and potentially leaking the first timer when the field is overwritten). Consider guarding with isRunning() (set by super.start()) and initializing the timer before the initial cache fill so the second concurrent call returns immediately.
This issue also appears on line 116 of the same file.
public void start() throws OperatorException {
if (timer != null) {
return;
}
super.start();
Sorry, something went wrong.
csviri
added a commit
to csviri/java-operator-sdk
that referenced
this pull request
Aug 3, 2026
operator-framework#3523) `PollingEventSource` held its timer in a final field initialised at construction: private final Timer timer = new Timer(); Two problems follow from that. The event source cannot be restarted. `stop()` calls `timer.cancel()` and a cancelled `java.util.Timer` cannot be reused, so a subsequent `start()` fails with `IllegalStateException: Timer already cancelled`. Restart is a supported lifecycle - `Operator.stop()` / `start()` recreates the thread pools for exactly this reason, and `TimerEventSource` creates a new `Timer` inside `start()`. The timer thread is not a daemon and is created eagerly. Merely constructing a `PollingEventSource` therefore starts a non-daemon thread that keeps the JVM from exiting, even if the event source is never started, and it outlives an operator that is stopped without stopping its event sources. `TimerEventSource` uses `new Timer(true)`. The timer is now created in `start()` as a daemon and cleared in `stop()`, matching `TimerEventSource`. Adds regression tests for restart and for the daemon flag; the restart one fails with `IllegalStateException: Timer already cancelled` without this change. Note: `PerResourcePollingEventSource` has a related restart limitation because `stop()` calls `shutdownNow()` on the `ScheduledExecutorService` from its configuration. That executor is supplied by the caller, so changing its ownership semantics is a separate discussion and is left out of this change. Co-authored-by: Copilot Autofix powered by AI <175728472+Copilot@users.noreply.github.com>
This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
Add this suggestion to a batch that can be applied as a single commit.This suggestion is invalid because no changes were made to the code.Suggestions cannot be applied while the pull request is closed.Suggestions cannot be applied while viewing a subset of changes.Only one suggestion per line can be applied in a batch.Add this suggestion to a batch that can be applied as a single commit.Applying suggestions on deleted lines is not supported.You must change the existing code in this line in order to create a valid suggestion.Outdated suggestions cannot be applied.This suggestion has been applied or marked resolved.Suggestions cannot be applied from pending reviews.Suggestions cannot be applied on multi-line comments.Suggestions cannot be applied while the pull request is queued to merge.Suggestion cannot be applied right now. Please check back later.
PollingEventSource held its timer in a final field initialised at
construction:
Two problems follow from that.
The event source cannot be restarted. stop() calls timer.cancel() and
a cancelled java.util.Timer cannot be reused, so a subsequent start()
fails with IllegalStateException: Timer already cancelled. Restart is a
supported lifecycle - Operator.stop() / start() recreates the thread
pools for exactly this reason, and TimerEventSource creates a new
Timer inside start().
The timer thread is not a daemon and is created eagerly. Merely
constructing a PollingEventSource therefore starts a non-daemon thread
that keeps the JVM from exiting, even if the event source is never
started, and it outlives an operator that is stopped without stopping its
event sources. TimerEventSource uses new Timer(true).
The timer is now created in start() as a daemon and cleared in stop(),
matching TimerEventSource.
Adds regression tests for restart and for the daemon flag; the restart one
fails with IllegalStateException: Timer already cancelled without this
change.
Note: PerResourcePollingEventSource has a related restart limitation
because stop() calls shutdownNow() on the ScheduledExecutorService
from its configuration. That executor is supplied by the caller, so
changing its ownership semantics is a separate discussion and is left
out of this change.
Part of #3517