subscription: fix producer goroutine leak on context cancel

[hsieh]

The producer in ExecuteSubscription sent results with a bare unbuffered send that did not select on p.Context.Done(). When a subscriber unsubscribes or disconnects and stops reading resultChannel, the producer blocks forever on the send; cancelling the context cannot unblock it because the goroutine is not in a select at that moment. This leaks one goroutine per unsubscribed subscription.

Wrap the send in a select that also observes p.Context.Done(), so a cancelled context lets the producer exit and close resultChannel even with no active receiver.

Add TestProducerExitsOnContextCancel as a regression test.

Summary by CodeRabbit

• Bug Fixes

  • Improved subscription handling when a request is cancelled, preventing stalled operations and ensuring result channels close cleanly.
  • Subscription producers now exit promptly instead of remaining active when no receiver is available.

• Tests

  • Added regression coverage for subscription cancellation and producer shutdown behavior.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro Plus

Run ID: 23bc8ed6-afaf-4b9d-adfa-a52d500df25b

📥 Commits

Reviewing files that changed from the base of the PR and between 6acef35 and 1a4d863.

📒 Files selected for processing (2)

• subscription.go
• subscription_leak_test.go

Included review availability: Your plan provides up to 10 included reviews per hour; 7 remain after this review.

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📝 Walkthrough

Walkthrough

Subscription result forwarding now checks the execution context before each send. A regression test verifies that cancelling a blocked subscription closes the result channel and exits the producer.

Changes

Subscription cancellation handling

Layer / File(s)	Summary
Cancellation-aware result forwarding subscription.go, subscription_leak_test.go	The producer returns when p.Context is cancelled instead of blocking on resultChannel. The regression test covers cancellation while the producer is blocked.

Estimated code review effort: 2 (Simple) | ~10 minutes

Merge Risk: ⚪ Minimal · up to 1a4d8

The change makes subscription producers stop cleanly when their context is cancelled and adds a regression test; no actionable merge-blocking risk remains beyond normal checks and review.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and concisely describes the main change: fixing the producer goroutine leak when the subscription context is cancelled.
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 2 functions across 2 files.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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[coveralls]

coverage: 95.805% (-0.009%) from 95.814% — hsieh:master into graphql-go:master