Document mutex responsibilities

Use Thread Safety Analysis (TSA) annotations to explicitly document which mutexes protect which variables, making thread safety relationships clear to both static analyzers and code readers.

Every mutex should have a clear, documented purpose with TSA annotations that specify what data it protects. This prevents issues like unused mutexes, inconsistent locking patterns, and unclear concurrent access semantics.

Example using TSA annotations:

class XRayInstrumentationManager {
private:
    mutable std::mutex functions_mutex;
    std::list<InstrumentedFunctionInfo> instrumented_functions GUARDED_BY(functions_mutex);
    
    InstrumentedFunctions getInstrumentedFunctions() const REQUIRES(functions_mutex) {
        std::lock_guard lock(functions_mutex);
        return instrumented_functions;
    }
};

For read-only concurrent access, use const-correctness and shared locks with clear documentation:

// Functions can access this info in parallel for reading purposes only
std::pair<const IndexContextInfoPtr, std::shared_lock<std::shared_mutex>> getIndexInfo() const;

TSA macros like GUARDED_BY, REQUIRES, and EXCLUDES help catch threading issues early and make code self-documenting about its concurrency assumptions.