[FSSDK-11900] fix: potential concurrent issue for cmab decision

[muzahidul-opti]

Summary

• Introduce a lock array to prevent race conditions
• Implement getLockIndex method for calculating lock index based on user and rule IDs

Test plan

• All test cases should be passed

Issues

• FSSDK-11900

[Copilot]

Pull Request Overview

This PR addresses a potential race condition in the CMAB decision-making process by implementing a lock array mechanism to ensure thread-safe access to decision operations.

• Introduces an array of 1000 NSLock objects to manage concurrent access
• Implements a hash-based lock selection strategy using user and rule IDs to distribute lock contention

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[Copilot]

Pull Request Overview

Copilot reviewed 1 out of 1 changed files in this pull request and generated 2 comments.

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[Copilot]

The conversion from UInt32 to Int could result in a negative value on platforms where Int is 32-bit, leading to a potential crash when accessing the locks array. Use Int(hashValue % UInt32(Self.NUM_LOCKS)) to ensure the modulo operation happens before conversion.

Suggested change

	let lockIndex = Int(hashValue) % Self.NUM_LOCKS
	let lockIndex = Int(hashValue % UInt32(Self.NUM_LOCKS))

[Copilot]

Using a semaphore to block while holding a lock can lead to deadlock if the asynchronous callback in getDecision attempts to acquire the same lock. The lock should be released before waiting on the semaphore, or the async operation should be moved outside the lock scope.