fix: service group not working well when callback takes long time

[kevwan]

fix #4261

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 94.58%. Comparing base (8690859) to head (72cb332).
Report is 194 commits behind head on master.

Additional details and impacted files

Files with missing lines	Coverage Δ
core/proc/shutdown.go	75.51% <100.00%> (+1.59%)	⬆️
core/service/servicegroup.go	100.00% <100.00%> (ø)
gateway/server.go	72.59% <100.00%> (+3.68%)	⬆️

... and 7 files with indirect coverage changes

[kevwan]

I'll help you review this pull request. Let me analyze the changes using the available tools.

Let me provide a thorough code review of the changes in PR #4531:

Key Changes:

1. Improved Shutdown Handling (core/proc/shutdown.go):

• Added explanatory comments about returning waitGroup.Wait
• Good practice to improve code readability while maintaining functionality
• The comment explains why an extra closure is created despite seeming redundant

2. Service Group Improvements (core/service/servicegroup.go):

• Enhanced parallel shutdown handling using threading.NewRoutineGroup()
• Important fix for Go closure issue with loop variables
• Added proper wait mechanism with group.Wait()
• Good practice: Added comment referencing the Go FAQ about closures and goroutines

3. Gateway Server Enhancements (gateway/server.go):

• Added tracking of gRPC connections through conns []zrpc.Client
• Improved shutdown sequence by stopping HTTP server before closing gRPC connections
• Implemented parallel connection closing using threading.NewRoutineGroup
• Good handling of connection close errors (ignoring them during shutdown)
• Fixed potential closure issues in connection handling

4. Test Improvements:

• Added new test cases for multiple services shutdown scenario
• Uses atomic operations for thread-safe testing
• Added proper tests for both shutdown and wrap-up scenarios
• Minor documentation improvement (MacOS capitalization fix)

Positive Aspects:

1. Thread-safety improvements throughout the codebase
2. Better resource cleanup during shutdown
3. Parallel processing for performance optimization
4. Well-documented changes with clear comments
5. Proper test coverage for new functionality
6. Good attention to Go-specific issues (closure handling)

Suggestions for Improvement:

1. Consider adding log statements during shutdown sequence for better debugging
2. Could add timeouts for the group.Wait() calls to prevent potential hangs
3. Consider documenting the order of shutdown importance in comments

Overall Assessment:
This is a high-quality PR that improves the shutdown handling and resource management of the system. The changes are well-tested, properly documented, and follow good coding practices. Special attention has been paid to concurrent operation safety and proper resource cleanup.

The changes appear safe to merge, as they:

• Don't break existing functionality
• Add proper test coverage
• Handle edge cases (like closure issues)
• Improve system shutdown reliability