fix panic

[daviszhen]

User description

What type of PR is this?

• API-change
• BUG
• Improvement
• Documentation
• Feature
• Test and CI
• Code Refactoring

Which issue(s) this PR fixes:

issue ##16724

#16752

What this PR does / why we need it:

修改在mo server还未启动时metric就开始执行的时序问题。

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PR Type

Bug fix, Enhancement

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Description

• Added functionality to ensure metrics and storage usage calculations wait for the MO server to start.
• Introduced thread safety in NullResp methods by adding mutex locking.
• Reordered imports in cmd/mo-service/main.go for consistency.

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Changes walkthrough 📝

	Relevant files
Enhancement	main.go Ensure metrics initialization waits for server start          cmd/mo-service/main.go Added mometric.WithFrontendServerStarted to InitMetric call. Reordered imports for consistency. +6/-3      server.go Track and check MO server start state                                        pkg/frontend/server.go Added moServerStarted atomic boolean to track server start state. Updated Start method to set moServerStarted to true upon successful start. Added MoServerIsStarted and setMoServerStarted functions. +17/-2    cron_task.go Ensure storage usage calculation waits for server start    pkg/util/metric/mometric/cron_task.go Added frontendServerStarted function to check server start state. Updated CalculateStorageUsage to wait for server start. +16/-8    metric.go Add frontend server start check to metric options                pkg/util/metric/mometric/metric.go Added frontendServerStarted to InitOptions. Added WithFrontendServerStarted option to set frontendServerStarted. +9/-0
Bug fix	resp_client.go Add thread safety to `NullResp` methods                                    pkg/frontend/resp_client.go Added mutex locking to NullResp methods for thread safety. +12/-0

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PR Reviewer Guide 🔍

⏱️ Estimated effort to review [1-5]	3
🧪 Relevant tests	No
🔒 Security concerns	No
⚡ Key issues to review	Thread Safety: The use of mutex in NullResp methods to ensure thread safety is a good practice. However, it's important to ensure that all methods that modify or access the shared state are properly synchronized.
	Metric Initialization Timing: The modification to delay metric initialization until the server starts is crucial to avoid race conditions. Reviewers should ensure that the implementation correctly handles all edge cases where the server might not start as expected.
	Error Handling: In the Start method of MOServer, the error handling after attempting to start the application should be reviewed to ensure that it properly handles and logs errors.

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PR Code Suggestions ✨

Category	Suggestion	Score
Possible issue	Use a defer statement to ensure the cancel function is called to avoid potential memory leaks To avoid potential memory leaks, ensure that the cancel function is called in the CalculateStorageUsage function by using a defer statement. pkg/util/metric/mometric/cron_task.go [124] ctx, cancel := context.WithCancel(ctx) +defer cancel() Apply this suggestion Suggestion importance[1-10]: 9 Why: This suggestion addresses a potential resource leak by ensuring that the cancel function is always called, which is critical for resource management and avoiding memory leaks in long-running processes.	9
Best practice	Use a defer statement to ensure the server started status is set even if an error occurs To ensure that setMoServerStarted is always called even if mo.app.Start() returns an error, consider using a defer statement to set the server started status. pkg/frontend/server.go [70-74] err := mo.app.Start() +defer setMoServerStarted(true) if err != nil { return err } -setMoServerStarted(true) Apply this suggestion Suggestion importance[1-10]: 8 Why: Using a defer statement for setMoServerStarted(true) ensures that the server's started status is reliably set, which is crucial for the correct functioning of the server, especially in error scenarios.	8
Performance	Use sync.RWMutex instead of sync.Mutex for better performance with more reads than writes Instead of using sync.Mutex directly in the NullResp struct, consider using sync.RWMutex to allow multiple readers and a single writer, which can improve performance when there are more reads than writes. pkg/frontend/resp_client.go [166] -sync.Mutex +sync.RWMutex Apply this suggestion Suggestion importance[1-10]: 7 Why: This is a valid suggestion for performance improvement, especially if the NullResp struct is read frequently compared to how often it is written to.	7
Readability	Break down the InitMetric call into multiple lines for better readability To improve readability and maintainability, consider breaking the InitMetric call into multiple lines with each parameter on a new line. This will make it easier to see all the parameters being passed. cmd/mo-service/main.go [490-493] -if act := mometric.InitMetric(ctx, nil, &SV, UUID, nodeRole, +if act := mometric.InitMetric( + ctx, nil, &SV, UUID, nodeRole, mometric.WithWriterFactory(writerFactory), mometric.WithFrontendServerStarted(frontend.MoServerIsStarted), ); !act { Apply this suggestion Suggestion importance[1-10]: 6 Why: The suggestion correctly identifies a readability improvement in the InitMetric call by breaking it into multiple lines, making the parameters more visible.	6