Channel implementation

Channel.swift

public class Channel<Value> {
    
    private class Subscription {
        
        weak var object: AnyObject?
        private let notifyBlock: (Value) -> Void
        private let queue: DispatchQueue
        
        var isValid: Bool {
            return object != nil
        }
        
        init(object: AnyObject?, queue: DispatchQueue, notifyBlock: @escaping (Value) -> Void) {
            self.object = object
            self.queue = queue
            self.notifyBlock = notifyBlock
        }
        
        func notify(_ value: Value) {
            queue.async { [weak self] in
                guard let strongSelf = self, strongSelf.isValid else { return }
                strongSelf.notifyBlock(value)
            }
        }
    }
    
    private var subscriptions: Protected<[Subscription]> = Protected([])
    
    public init() { }
    
    public func subscribe(_ object: AnyObject?, queue: DispatchQueue = .main, notifyBlock: @escaping (Value) -> Void) {
        let subscription = Subscription(object: object, queue: queue, notifyBlock: notifyBlock)
        
        subscriptions.write { subscriptions in
            subscriptions.append(subscription)
        }
    }
    
    public func unsubscribe(_ object: AnyObject?) {
        subscriptions.write { list in
            if let foundIndex = list.index(where: { $0.object === object }) {
                list.remove(at: foundIndex)
            }
        }
    }
    
    public func broadcast(_ value: Value) {
        subscriptions.write { list in
            list = list.filter({ $0.isValid })
            list.forEach({ $0.notify(value) })
        }
    }
}

public class Protected<Value> {
    
    private var queue = DispatchQueue(label: "me.gk.Lightning.Protected", attributes: .concurrent)
    private var _value: Value
    
    public var value: Value {
        get {
            return queue.sync {
                return _value
            }
        }
        set {
            queue.async(flags: .barrier) { [weak self] in
                self?._value = newValue
            }
        }
    }
    
    public init(_ value: Value) {
        _value = value
    }
    
    public func read(_ block: (Value) -> Void) {
        queue.sync {
            block(_value)
        }
    }
    
    public func write(_ block: @escaping (inout Value) -> Void) {
        queue.async(flags: .barrier) { [weak self] in
            guard let strongSelf = self else { return }
            block(&strongSelf._value)
        }
    }
}