NSLock

public struct Cache {
    
    private static var data = [String:Any]()
    
//    private static var lock = DispatchSemaphore(value: 1)
    private static var lock = NSLock()
    
    public static func get(_ key:String) -> Any? {
        
        data[key]
        
    }
    
    public static func set(_ key:String,_ value:Any) {
        
        lock.lock()
        
        defer {
            lock.unlock()
        }
        data[key] = value
        
    }
}

NSRecursiveLock

递归锁

public struct Cache {
    
    private static var data = [String:Any]()
    
//    private static var lock = DispatchSemaphore(value: 1)
//    private static var lock = NSLock()
    private static var lock = NSRecursiveLock()
    
    public static func get(_ key:String) -> Any? {
        
        data[key]
        
    }
    
    public static func set(_ key:String,_ value:Any) {
        
        lock.lock()
        
        defer {
            lock.unlock()
        }
        data[key] = value
        
    }
}

当发生自己调用自己的时候，或者递归的时候，需要使用递归锁NSRecursiveLock，用法跟NSLock是一样的，只是使用场景可能不一样。