fix: goroutine leaks in event executor and improve shutdown handling

[beeme1mr]

This PR

• properly shuts down the event executor

Related Issues

Fixes #471

Notes

Added go.uber.org/goleak to try and detect other leaks.

How to test

Run test suite

[gemini-code-assist]

Summary of Changes

Hello @beeme1mr, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request significantly improves the stability and resource management of the OpenFeature SDK by addressing potential goroutine leaks within the event executor. It introduces a robust shutdown mechanism that ensures all background event processing routines are properly terminated when no longer needed, and integrates a powerful leak detection tool to safeguard against future concurrency issues. These changes enhance the overall reliability of the SDK, particularly in long-running applications or scenarios involving frequent provider changes.

Highlights

• Goroutine Leak Prevention: Implemented a comprehensive shutdown mechanism for the eventExecutor to prevent goroutine leaks, utilizing sync.Once, sync.WaitGroup, and dedicated done channels for graceful termination of event processing goroutines.
• Enhanced Shutdown Handling: Modified Shutdown() and ShutdownWithContext() functions, as well as initSingleton(), to explicitly call the new eventExecutor shutdown logic, ensuring all associated goroutines are cleaned up when the OpenFeature SDK is reset or shut down.
• Goroutine Leak Detection: Integrated go.uber.org/goleak into the test suite and added new tests (TestNoGoroutineLeak, TestNoGoroutineLeakWithMultipleProviders, TestNoGoroutineLeakWithShutdownWithContext) to automatically detect and prevent future goroutine leaks.
• Test Utility Refactoring: Introduced helper functions expectChannelReceive and expectTimeout in tests to simplify and standardize assertions related to channel operations, improving test readability and reliability.
• Buffered Shutdown Semaphore: Changed the shutdownSemaphore in providerReference to a buffered channel, allowing for more robust signaling during shutdown without blocking.

Changelog

• go.mod
  • Added go.uber.org/goleak dependency for goroutine leak detection.
• go.sum
  • Updated checksums to include go.uber.org/goleak and removed outdated golang.org/x/sync and golang.org/x/text entries.
• openfeature/client_test.go
  • Removed unused math import.
  • Modified TestRequirement_1_7_6 to include event executor shutdown in cleanup and use a controlled blocking channel for provider initialization testing.
• openfeature/event_executor.go
  • Added shutdownOnce, done channel, and sync.WaitGroup to eventExecutor for controlled shutdown.
  • Initialized the done channel in newEventExecutor.
  • Updated startListeningAndShutdownOld to track goroutines with WaitGroup and listen for shutdown signals.
  • Refactored startEventListener to use WaitGroup and a select statement for graceful termination upon done channel closure.
  • Implemented a shutdown() method to signal, wait for, and drain event executor goroutines.
• openfeature/event_executor_test.go
  • Imported go.uber.org/goleak.
  • Modified TestEventHandler_multiSubs to ensure goroutines are cleanly shut down during test cleanup.
  • Added TestBasicShutdown to verify the shutdown() method's functionality.
  • Added TestNoGoroutineLeakWithMultipleProviders to confirm no goroutine leaks occur with multiple registered providers using goleak.VerifyNone.
• openfeature/main_test.go
  • Added TestMain to ensure global event executor shutdown after all tests complete, preventing cross-test goroutine leaks.
• openfeature/openfeature.go
  • Modified initSingleton() to shut down any existing event executor before reinitialization.
  • Updated Shutdown() and ShutdownWithContext() to explicitly shut down the event executor before reinitializing the singleton.
• openfeature/openfeature_test.go
  • Imported context and go.uber.org/goleak.
  • Replaced direct select statements with new expectChannelReceive and expectTimeout helper functions for channel assertions.
  • Added expectChannelReceive and expectTimeout helper functions for robust channel testing.
  • Added TestNoGoroutineLeak to verify proper goroutine cleanup after event processing and shutdown.
  • Added TestNoGoroutineLeakWithShutdownWithContext to ensure ShutdownWithContext also prevents goroutine leaks.
• openfeature/reference.go
  • Changed shutdownSemaphore in providerReference to a buffered channel to prevent blocking during shutdown signaling.

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[gemini-code-assist]

Code Review

This is an excellent pull request that addresses a critical issue of potential goroutine leaks in the event executor. The implementation of a graceful shutdown mechanism using standard concurrency primitives like sync.WaitGroup, sync.Once, and a done channel is well-executed and robust. The addition of go.uber.org/goleak and the comprehensive new tests that verify the absence of leaks are particularly commendable, as they significantly improve the reliability of the library. The refactoring of existing tests to prevent leaks and improve readability is also a great enhancement. I have one minor suggestion to make the channel draining logic in the shutdown method more idiomatic and robust.

[gemini-code-assist]

While the current approach to draining the event channel is likely safe because all producer goroutines should have been stopped and waited for via e.wg.Wait(), using len(e.eventChan) in a loop can be racy if there are concurrent writers. A more robust and idiomatic way to drain a channel non-blockingly is to use a select with a default case. This ensures that the drain operation is safe even if future code changes inadvertently introduce a race condition.

for {
			select {
			case <-e.eventChan:
			default:
				return
			}
		}