先来看看核心代码subscribe
override func subscribe(_ observer: O) -> Disposable where O.E == Element {
if !CurrentThreadScheduler.isScheduleRequired {
// The returned disposable needs to release all references once it was disposed.
let disposer = SinkDisposer()
let sinkAndSubscription = run(observer, cancel: disposer)
disposer.setSinkAndSubscription(sink: sinkAndSubscription.sink, subscription: sinkAndSubscription.subscription)
return disposer
}
else {
return CurrentThreadScheduler.instance.schedule(()) { _ in
let disposer = SinkDisposer()
let sinkAndSubscription = self.run(observer, cancel: disposer)
disposer.setSinkAndSubscription(sink: sinkAndSubscription.sink, subscription: sinkAndSubscription.subscription)
return disposer
}
}
}
其实看代码是有技巧的，我一看到这个代码我就知道这个if..else是跟线程安全有关的，如果你重点关注线程安全的话，那么你就要仔细看线程安全的逻辑，如果你关注的是实现原理那么你看的核心实现逻辑，看代码的时候要选择性的忽略掉一些细节，集中精力放在你关注的问题上面。我现在重点关注的是schedule 逻辑。
public class CurrentThreadScheduler : ImmediateSchedulerType {
typealias ScheduleQueue = RxMutableBox>
/// The singleton instance of the current thread scheduler.
public static let instance = CurrentThreadScheduler()
private static var isScheduleRequiredKey: pthread_key_t = { () -> pthread_key_t in
let key = UnsafeMutablePointer.allocate(capacity: 1)
defer {
key.deallocate(capacity: 1)
}
guard pthread_key_create(key, nil) == 0 else {
rxFatalError("isScheduleRequired key creation failed")
}
return key.pointee
}()
private static var scheduleInProgressSentinel: UnsafeRawPointer = { () -> UnsafeRawPointer in
return UnsafeRawPointer(UnsafeMutablePointer.allocate(capacity: 1))
}()
static var queue : ScheduleQueue? {
get {
return Thread.getThreadLocalStorageValueForKey(CurrentThreadSchedulerQueueKey.instance)
}
set {
Thread.setThreadLocalStorageValue(newValue, forKey: CurrentThreadSchedulerQueueKey.instance)
}
}
/// Gets a value that indicates whether the caller must call a `schedule` method.
public static fileprivate(set) var isScheduleRequired: Bool {
get {
return pthread_getspecific(CurrentThreadScheduler.isScheduleRequiredKey) == nil
}
set(isScheduleRequired) {
if pthread_setspecific(CurrentThreadScheduler.isScheduleRequiredKey, isScheduleRequired ? nil : scheduleInProgressSentinel) != 0 {
rxFatalError("pthread_setspecific failed")
}
}
}
/**
Schedules an action to be executed as soon as possible on current thread.
If this method is called on some thread that doesn't have `CurrentThreadScheduler` installed, scheduler will be
automatically installed and uninstalled after all work is performed.
- parameter state: State passed to the action to be executed.
- parameter action: Action to be executed.
- returns: The disposable object used to cancel the scheduled action (best effort).
*/
public func schedule(_ state: StateType, action: @escaping (StateType) -> Disposable) -> Disposable {
if CurrentThreadScheduler.isScheduleRequired {
CurrentThreadScheduler.isScheduleRequired = false
let disposable = action(state)
defer {
CurrentThreadScheduler.isScheduleRequired = true
CurrentThreadScheduler.queue = nil
}
guard let queue = CurrentThreadScheduler.queue else {
return disposable
}
while let latest = queue.value.dequeue() {
if latest.isDisposed {
continue
}
latest.invoke()
}
return disposable
}
let existingQueue = CurrentThreadScheduler.queue
let queue: RxMutableBox>
if let existingQueue = existingQueue {
queue = existingQueue
}
else {
queue = RxMutableBox(Queue(capacity: 1))
CurrentThreadScheduler.queue = queue
}
let scheduledItem = ScheduledItem(action: action, state: state)
queue.value.enqueue(scheduledItem)
return scheduledItem
}
}
代码有点长，拆开一点点看
typealias ScheduleQueue = RxMutableBox>
Box:你可以理解为黑盒，里面装着实物，做这个封装是为了忽视细节。打个比方对于货车司机来说他才不管你具体装的什么货呢？他只关心目的地在哪，只有发货方和收货方才需要关注具体货物是什么，这样做一层抽象有利于中间层的运输。类似的就要系统的Optional类型
Queue: 是一个可扩展循环队列，遵循先进先出原则，add和remove算法复杂度都为O(1),可根据元素数量自适应大小，通过设置游标达到访问元素的目的，具体参见Queue.Swift
private static var isScheduleRequiredKey: pthread_key_t = { () -> pthread_key_t in
let key = UnsafeMutablePointer.allocate(capacity: 1)
defer {
key.deallocate(capacity: 1)
}
guard pthread_key_create(key, nil) == 0 else {
rxFatalError("isScheduleRequired key creation failed")
}
return key.pointee
}()
这是一个底层api，为线程开辟一个私有空间存储线程数据
相关文章： pthread_key_create
static var queue : ScheduleQueue? {
get {
return Thread.getThreadLocalStorageValueForKey(CurrentThreadSchedulerQueueKey.instance)
}
set {
Thread.setThreadLocalStorageValue(newValue, forKey: CurrentThreadSchedulerQueueKey.instance)
}
}
与上面的功能类似，不同的是使用的NSThread的API,相对上面的api要高级一点，为当前线程开辟一片空间用来存储queue类型数据
public static fileprivate(set) var isScheduleRequired: Bool {
get {
return pthread_getspecific(CurrentThreadScheduler.isScheduleRequiredKey) == nil
}
set(isScheduleRequired) {
if pthread_setspecific(CurrentThreadScheduler.isScheduleRequiredKey, isScheduleRequired ? nil : scheduleInProgressSentinel) != 0 {
rxFatalError("pthread_setspecific failed")
}
}
}
这个比较简单设置isScheduleRequired {get , set}属性注意这里的数据都是针对线程的不同于以往的数据属于对象。
public func schedule(_ state: StateType, action: @escaping (StateType) -> Disposable) -> Disposable {
if CurrentThreadScheduler.isScheduleRequired {
CurrentThreadScheduler.isScheduleRequired = false
let disposable = action(state)
defer {
CurrentThreadScheduler.isScheduleRequired = true
CurrentThreadScheduler.queue = nil
}
guard let queue = CurrentThreadScheduler.queue else {
return disposable
}
while let latest = queue.value.dequeue() {
if latest.isDisposed {
continue
}
latest.invoke()
}
return disposable
}
let existingQueue = CurrentThreadScheduler.queue
let queue: RxMutableBox>
if let existingQueue = existingQueue {
queue = existingQueue
}
else {
queue = RxMutableBox(Queue(capacity: 1))
CurrentThreadScheduler.queue = queue
}
let scheduledItem = ScheduledItem(action: action, state: state)
queue.value.enqueue(scheduledItem)
return scheduledItem
}
这个是核心代码schedule， 通过设置flag判断当前是否有task在执行，如果有则将task加入到待处理的队列中去。当线程处理完当前task后，会检测是否还有为执行的task，然后依次执行为执行的task
官方测试代码
func testCurrentThreadScheduler_basicScenario() {
XCTAssertTrue(CurrentThreadScheduler.isScheduleRequired)
var messages = [Int]()
_ = CurrentThreadScheduler.instance.schedule(()) { s in
messages.append(1)
_ = CurrentThreadScheduler.instance.schedule(()) { s in
messages.append(3)
_ = CurrentThreadScheduler.instance.schedule(()) {
messages.append(5)
return Disposables.create()
}
messages.append(4)
return Disposables.create()
}
messages.append(2)
return Disposables.create()
}
XCTAssertEqual(messages, [1, 2, 3, 4, 5])
}