takeUntil运算

说明：
Returns the elements from the source observable sequence until the other observable sequence produces an element.，含义说明如下图:

屏幕快照 2016-03-13 上午8.20.34.png

代码如下：

extension ObservableType {
    public func takeUntil(other: O)->Observable {
        return TakeUntil(source: asObservable(), other: other.asObservable())
    }
}

class TakeUntil: Producer {
    private let _source: Observable
    private let _other: Observable

    init(source: Observable, other: Observable) {
        _source = source
        _other = other
    }

    override func run(observer: O)->Disposable {
        let sink = TakeUntilSink(parent: self, observer: observer)
        sink.disposable = sink.run()
        return sink
    }
}

class TakeUntilSink: Sink, LockOwnerType, ObserverType, SynchronizedOnType {
    typealias E = ElementType
    typealias Parent = TakeUntil

    private let _parent: Parent

    let _lock = NSRecursiveLock()

    // state
    private var _open = false

    init(parent: Parent, observer: O) {
        _parent = parent
        super.init(observer: observer)
    }

    func on(event: Event) {
        synchronizedOn(event)
    }

    func _synchronized_on(event: Event) {
        switch event {
        case .Next:
            forwardOn(event)
        case .Error:
            forwardOn(event)
            dispose()
        case .Completed:
            forwardOn(event)
            dispose()
        }
    }

    func run()->Disposable {
        let otherObserver = TakeUntilSinkOther(parent: self)
        let otherSubscription = _parent._other.subscribe(otherObserver)
        otherObserver._subscription.disposable = otherSUbscription
        let sourceSubscription = _parent._source.subscribe(self)

        return StableCompositeDisposable.create(sourceSubscription, otherObserver._subscription)
    }
}

class TakeUntilSinkOther: ObserverType, LockOwnerType, SynchronizedOnType {
    typealias Parent = TakeUntilSink
    typealias E = Other
    
    private let _parent: Parent

    var _lock: NSRecursiveLock {
        return _parent._lock
    }

    private let _subscription = SingleAssignmentDisposable()
    
    init(parent: Parent) {
        _parent = parent
    }

    func on(event: Event) {
        synchronizedOn(event)
    }

    func _synchronized_on(event: Event) {
        switch event {
        case .Next:
            _parent.forwardOn(.Completed)
            _parent.dispose()
        case .Error(let e):
            _parent.forwardOn(.Error(e))
            _parent.dispose()
        case .Completed:
            _parent._open = true
            _subscription.dispose()
        }
    }  

    deinit {

    }
}