perf: optimize usage of RWMutex in MCPServer for performance

[cryo-zd]

  Note that field capabilitiesMu is a RWMutex in MCPServer for controlling concurrent read/write operations to field capabilities.
 At most of time, capabilities 's members resource/tools/prompts/ will only be set not to be nil for one time when we call func NewMCPServer at the beginning or when we call func AddResource/AddResourceTemplate/AddPrompt/AddTools for the first time.
  So, for field capabilitiesMu, the number of its read operations far exceeds the number of write operations, for which we could utilize RLock and double-checking technique to optimizes the concurrency performance for the AddXxx functions mentioned above.
experiment

Summary by CodeRabbit

• Refactor
  • Enhanced internal performance and responsiveness when adding resources, templates, prompts, or tools. No changes to user-facing features or functionality.

[coderabbitai]

Walkthrough

This change updates the locking mechanism in the MCPServer struct methods responsible for adding resources, resource templates, prompts, and tools. Instead of always acquiring an exclusive lock to check and initialize capability fields, the code now uses a double-checked locking pattern: it first checks the field under a shared read lock, only escalating to an exclusive lock if initialization is required. This reduces the duration of exclusive lock holding on capabilitiesMu. No public API signatures were altered.

Changes

Files/Paths	Change Summary
server/server.go	Refactored locking in AddResource, AddResourceTemplate, AddPrompt, and AddTools to use double-checked locking with capabilitiesMu, reducing exclusive lock contention during capability initialization.

Possibly related PRs

• Fix tool calls #38: Also modifies capability initialization in server.go, changing from eager to lazy initialization in the same methods affected by this PR.
• Dustin/138 deadlock remove global mutex #139: Introduces and restructures mutex usage, including capabilitiesMu, which this PR further refines with double-checked locking.

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• server/server.go (4 hunks)

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• server/server.go

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