什么是 Scheduler ?

Scheduler 就是一個程序上下文發(fā)生的地方，它可以是一個線程，一個 dispatch queue 或者 NSOperation，例如下面的圖片所示：

image.png

闡明 Scheduler

有一個錯誤的觀點就是 schedulers 等價于一個 thread,這樣看起來好像很合理，schedulers 就像 GCD.

但是如果以自定義 scheduler 的時候，可以創(chuàng)建多個 scheduler 使用相同的線程

explicit

這里要記住的是 schedulers 并不是線程，它也沒有和線程有一一對應的關(guān)系

下面是例子用到的一些代碼

fileprivate func secondsElapsed() -> String {
  return String(format: "%02i", Int(Date().timeIntervalSince(start).rounded()))
}

extension ObservableType {
  func dump() -> RxSwift.Observable<Self.E> {
    return self.do(onNext: { element in
      let threadName = getThreadName()
      print("\(secondsElapsed())s | [D] \(element) received on \(threadName)")
    })
  }
  
  func dumpingSubscription() -> Disposable {
    return self.subscribe(onNext: { element in
      let threadName = getThreadName()
      print("\(secondsElapsed())s | [S] \(element) received on \(threadName)")
    })
  }
}

接下來寫下如下代碼

let fruit = Observable<String>.create { (observer) -> Disposable in
    observer.onNext("[apple]")
    sleep(2)
    observer.onNext("[pineapple]")
    sleep(2)
    observer.onNext("[strawberryy]")
    return Disposables.create()
}

輸入如下

00s | [D] [apple] received on Main Thread
00s | [S] [apple] received on Main Thread
02s | [D] [pineapple] received on Main Thread
02s | [S] [pineapple] received on Main Thread
04s | [D] [strawberryy] received on Main Thread
04s | [S] [strawberryy] received on Main Thread

使用 subscribeOn

有時候要改變 schedule 的 observable 的運行的地方。創(chuàng)建一個 scheduler,然后改成如下代碼

let globalScheduler = ConcurrentDispatchQueueScheduler(queue: DispatchQueue.global())

fruit
    .subscribeOn(globalScheduler)
    .dump()
    .dumpingSubscription()
    .addDisposableTo(bag)
    
RunLoop.main.run(until: Date(timeIntervalSinceNow: 13))
    

輸出如下

00s | [D] [apple] received on Anonymous Thread
00s | [S] [apple] received on Anonymous Thread
02s | [D] [pineapple] received on Anonymous Thread
02s | [S] [pineapple] received on Anonymous Thread
04s | [D] [strawberryy] received on Anonymous Thread
04s | [S] [strawberryy] received on Anonymous Thread

使用 observeOn

把代碼改成如下:

fruit
    .subscribeOn(globalScheduler)
    .dump()
    .observeOn(MainScheduler.instance)
    .dumpingSubscription()
    .addDisposableTo(bag)
    

輸出:

00s | [D] [apple] received on Anonymous Thread
00s | [S] [apple] received on Main Thread
02s | [D] [pineapple] received on Anonymous Thread
02s | [S] [pineapple] received on Main Thread
04s | [D] [strawberryy] received on Anonymous Thread
04s | [S] [strawberryy] received on Main Thread