iOS开发GCD的13 个应用场景

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本文不涉及 GCD 的概念和理论,仅记录了 GCD 在一些开发场景下的应用。 欢迎大家积极留言补充。

耗时操作

这是应用最广泛的场景,为了避免阻塞主线程,将耗时操作放在子线程处理,然后在主线程使用处理结果。比如读取沙盒中的一些数据,然后将读取的数据展示在 UI,这个场景还有几个细分:

执行一个耗时操作后回调主线程
// 主线程需要子线程的处理结果
func handle<T>(somethingLong: @escaping () -> T, finshed: @escaping (T) -> ()) {
globalQueue.async {
let data = somethingLong()
self.mainQueue.async {
finshed(data)
}
}
}
// 主线程不需要子线程的处理结果
func handle(somethingLong: @escaping () -> (), finshed: @escaping () -> ()) {
let workItem = DispatchWorkItem {
somethingLong()
}
globalQueue.async(execute: workItem)
workItem.wait()
finshed()
}
=========================================================================
GCDKit().handle(somethingLong: { [weak self] in
self?.color = UIColor.red
sleep(2)
}) { [weak self] in
self?.view.backgroundColor = self?.color
}
GCDKit().handle(somethingLong: {
let p = Person()
p.age = 40
print(Date(), p.age)
sleep(2)
return p
}) { (p: Person) in
print(Date(), p.age)
}

串行耗时操作

每一段子任务依赖上一个任务完成,全部完成后回调主线程:

// 向全局并发队列添加任务,添加的任务会同步执行
func wait(code: @escaping GCDKitHandleBlock) -> GCDKit {
handleBlockArr.append(code)
return self
}
// 处理完毕的回调,在主线程异步执行
func finshed(code: @escaping GCDKitHandleBlock) {
globalQueue.async {
for workItem in self.handleBlockArr {
workItem()
}
self.handleBlockArr.removeAll()
self.mainQueue.async {
code()
}
}
}
=======================================================================
GCDKit().wait {
self.num += 1
}.wait {
self.num += 2
}.wait {
self.num += 3
}.wait {
self.num += 4
}.wait {
self.num += 5
}.finshed {
print(self.num, Thread.current)
}

并发耗时操作

每一段子任务独立,所有子任务完成后回调主线程:

// 向自定义并发队列添加任务,添加的任务会并发执行
func handle(code: @escaping GCDKitHandleBlock) -> GCDKit {
let queue = DispatchQueue(label: "", attributes: .concurrent)
let workItem = DispatchWorkItem {
code()
}
queue.async(group: group, execute: workItem)
return self
}
// 此任务执行时会排斥其他的并发任务,一般用于写入事务,保证线程安全。
func barrierHandle(code: @escaping GCDKitHandleBlock) -> GCDKit {
let queue = DispatchQueue(label: "", attributes: .concurrent)
let workItem = DispatchWorkItem(flags: .barrier) {
code()
}
queue.async(group: group, execute: workItem)
return self
}
// 处理完毕的回调,在主线程异步执行
func allDone(code: @escaping GCDKitHandleBlock) {
group.notify(queue: .main, execute: {
code()
})
}
======================================================================
GCDKit().barrierHandle {
self.num += 1
}.barrierHandle {
self.num += 2
}.barrierHandle {
self.num += 3
}.handle {
self.num += 4
}.handle {
self.num += 5
}.allDone {
self.num += 6
print(self.num, Thread.current)
}

延时执行

延时一段时间后执行代码,一般见于打开 App 一段时间后,弹出求好评对话框。

func run(when: DispatchTime, code: @escaping GCDKitHandleBlock) {
DispatchQueue.main.asyncAfter(deadline: when) {
code()
}
}
=======================================================================
GCDKit().run(when: .now() + .seconds(120)) {
self.doSomething()
}

定时器

由于 Timer 的 Target 是强引用,对于 Timer 的销毁需要特别处理,此外,Timer 的运行依赖于 Runloop,在 Runloop 的一次循环中,Timer 也只会执行一次,这使得在 Runloop 负担比较重时,可能会跳过 Timer 的执行,因此,在用到定时器的地方,你也可以用 CGD 的 TimerSource 替代:

// 计时器
// - Parameters:
//  - start: 开始时间
//  - end: 结束时间
//  - repeating: 多久重复一次
//  - leeway: 允许误差
//  - eventHandle: 处理事件
//  - cancelHandle: 计时器结束事件
func timer(start: DispatchTime,
end: DispatchTime,
repeating: Double,
leeway: DispatchTimeInterval,
eventHandle: @escaping GCDKitHandleBlock,
cancelHandle: GCDKitHandleBlock? = nil)
{
let timer = DispatchSource.makeTimerSource()
timer.setEventHandler {
eventHandle()
}
timer.setCancelHandler {
cancelHandle?()
}
timer.schedule(deadline: start, repeating: repeating, leeway: leeway)
timer.resume()
run(when: end) {
timer.cancel()
}
}
======================================================================
GCDKit().timer(start: .now(),
end: .now() + .seconds(10),
repeating: 2,
leeway: .milliseconds(1),
eventHandle: {
self.doSomething()
}) {
print("timer cancel")
}

并发遍历

如果你需要更快的处理数据,可以用 concurrentPerform 让循环操作并发执行:

func map<T>(data: [T], code: (T) -> ()) {
DispatchQueue.concurrentPerform(iterations: data.count) { (i) in
code(data[i])
}
}
func run(code: (Int) -> (), repeting: Int) {
DispatchQueue.concurrentPerform(iterations: repeting) { (i) in
code(i)
}
}
=======================================================================
let data = [1, 2, 3]
var sum = 0
GCDKit().map(data: data) { (ele: Int) in
sleep(1)
sum += ele
}
print(sum)
GCDKit().run(code: { (i) in
sleep(1)
sum += data[i]
}, repeting: data.count)
print(sum)

控制并发数

有时我们需要并发处理一些任务,但是并不想同时开很多线程,GCD 并没有类似 NSOperation 最大并发数的概念,但可以借助信号量实现:

func doSomething(label: String, cost: UInt32, complete:@escaping ()->()){
NSLog("Start task%@",label)
sleep(cost)
NSLog("End task%@",label)
complete()
}
======================================================================
let semaphore = DispatchSemaphore(value: 3)
let queue = DispatchQueue(label: "", qos: .default, attributes: .concurrent)
queue.async {
semaphore.wait()
self.doSomething(label: "1", cost: 2, complete: {
print(Thread.current)
semaphore.signal()
})
}
queue.async {
semaphore.wait()
self.doSomething(label: "2", cost: 2, complete: {
print(Thread.current)
semaphore.signal()
})
}
queue.async {
semaphore.wait()
self.doSomething(label: "3", cost: 4, complete: {
print(Thread.current)
semaphore.signal()
})
}
queue.async {
semaphore.wait()
self.doSomething(label: "4", cost: 2, complete: {
print(Thread.current)
semaphore.signal()
})
}
queue.async {
semaphore.wait()
self.doSomething(label: "5", cost: 3, complete: {
print(Thread.current)
semaphore.signal()
})
}

时序管理

时序管理主要有几种组合情况:

  • 子任务内是否开线程;
  • 子任务是否依次执行;

子任务内不开线程依次执行
参照耗时操作小节。

子任务内开线程依次执行

一般见于网络请求,一个接口的请求参数是另一个接口的返回值,这种情况就需要对网络请求进行时序管理,以下代码表示一个网络请求的封装:

func networkTask(label:String, cost:UInt32, complete:@escaping ()->()){
NSLog("Start network Task task%@",label)
DispatchQueue.global().async {
sleep(cost)
NSLog("End networkTask task%@",label)
DispatchQueue.main.async {
complete()
}
}
}
// 在子线程可开线程的情况下,依次执行需要借助信号量控制:
let group = DispatchGroup()
group.enter()
networkTask(label: "1", cost: 2, complete: {
group.leave()
})
group.enter()
networkTask(label: "2", cost: 4, complete: {
group.leave()
})
group.enter()
networkTask(label: "3", cost: 2, complete: {
group.leave()
})
group.enter()
networkTask(label: "4", cost: 4, complete: {
group.leave()
})
group.notify(queue: .main, execute:{
print("All network is done")
})
=======================================================================
2017-12-19 14:10:33.876393+0800 Demo[16495:4973791] Start network Task task1
2017-12-19 14:10:33.878869+0800 Demo[16495:4973791] Start network Task task2
2017-12-19 14:10:33.879142+0800 Demo[16495:4973791] Start network Task task3
2017-12-19 14:10:33.879309+0800 Demo[16495:4973791] Start network Task task4
2017-12-19 14:10:35.883851+0800 Demo[16495:4974025] End networkTask task1
2017-12-19 14:10:35.883850+0800 Demo[16495:4974030] End networkTask task3
2017-12-19 14:10:37.883995+0800 Demo[16495:4974026] End networkTask task2
2017-12-19 14:10:37.883995+0800 Demo[16495:4974027] End networkTask task4
All network is done
// 你也可以这样进行简写
let downloadGroup = DispatchGroup()
GCDKit().run(code: { (i) in
downloadGroup.enter()
networkTask(label: "(i)", cost: UInt32(i), complete: {
downloadGroup.leave()
})
}, repeting: 10)
downloadGroup.notify(queue: .main) {
print("All network is done")
}
=======================================================================
2017-12-19 15:07:13.253428+0800 Demo[49319:5169745] Start network Task task3
2017-12-19 15:07:13.253428+0800 Demo[49319:5169743] Start network Task task2
2017-12-19 15:07:13.253428+0800 Demo[49319:5169744] Start network Task task0
2017-12-19 15:07:13.253479+0800 Demo[49319:5169474] Start network Task task1
2017-12-19 15:07:13.253946+0800 Demo[49319:5169744] Start network Task task6
2017-12-19 15:07:13.253947+0800 Demo[49319:5169743] Start network Task task4
2017-12-19 15:07:13.253947+0800 Demo[49319:5169745] Start network Task task5
2017-12-19 15:07:13.254119+0800 Demo[49319:5169763] End networkTask task0
2017-12-19 15:07:13.254193+0800 Demo[49319:5169474] Start network Task task7
2017-12-19 15:07:13.254339+0800 Demo[49319:5169744] Start network Task task8
2017-12-19 15:07:13.254343+0800 Demo[49319:5169743] Start network Task task9
2017-12-19 15:07:14.258061+0800 Demo[49319:5169764] End networkTask task1
2017-12-19 15:07:15.258071+0800 Demo[49319:5169762] End networkTask task2
2017-12-19 15:07:16.258189+0800 Demo[49319:5169742] End networkTask task3
2017-12-19 15:07:17.258100+0800 Demo[49319:5169745] End networkTask task4
2017-12-19 15:07:18.258196+0800 Demo[49319:5169766] End networkTask task5
2017-12-19 15:07:19.258171+0800 Demo[49319:5169765] End networkTask task6
2017-12-19 15:07:20.259119+0800 Demo[49319:5169763] End networkTask task7
2017-12-19 15:07:21.258239+0800 Demo[49319:5169767] End networkTask task8
2017-12-19 15:07:22.258280+0800 Demo[49319:5169744] End networkTask task9
All network is done
子任务内开线程不依次执行

这种情况多见于需要请求多个接口,全部请求完毕后再进行某些操作,这可以借助 GCD 的任务组处理:

let group = DispatchGroup()
group.enter()
networkTask(label: "1", cost: 2, complete: {
group.leave()
})
group.enter()
networkTask(label: "2", cost: 4, complete: {
group.leave()
})
group.enter()
networkTask(label: "3", cost: 2, complete: {
group.leave()
})
group.enter()
networkTask(label: "4", cost: 4, complete: {
group.leave()
})
group.notify(queue: .main, execute:{
print("All network is done")
})
======================================================================
2017-12-19 14:10:33.876393+0800 Demo[16495:4973791] Start network Task task1
2017-12-19 14:10:33.878869+0800 Demo[16495:4973791] Start network Task task2
2017-12-19 14:10:33.879142+0800 Demo[16495:4973791] Start network Task task3
2017-12-19 14:10:33.879309+0800 Demo[16495:4973791] Start network Task task4
2017-12-19 14:10:35.883851+0800 Demo[16495:4974025] End networkTask task1
2017-12-19 14:10:35.883850+0800 Demo[16495:4974030] End networkTask task3
2017-12-19 14:10:37.883995+0800 Demo[16495:4974026] End networkTask task2
2017-12-19 14:10:37.883995+0800 Demo[16495:4974027] End networkTask task4
All network is done
// 你也可以这样进行简写
let downloadGroup = DispatchGroup()
GCDKit().run(code: { (i) in
downloadGroup.enter()
networkTask(label: "(i)", cost: UInt32(i), complete: {
downloadGroup.leave()
})
}, repeting: 10)
downloadGroup.notify(queue: .main) {
print("All network is done")
}
=======================================================================
2017-12-19 15:07:13.253428+0800 Demo[49319:5169745] Start network Task task3
2017-12-19 15:07:13.253428+0800 Demo[49319:5169743] Start network Task task2
2017-12-19 15:07:13.253428+0800 Demo[49319:5169744] Start network Task task0
2017-12-19 15:07:13.253479+0800 Demo[49319:5169474] Start network Task task1
2017-12-19 15:07:13.253946+0800 Demo[49319:5169744] Start network Task task6
2017-12-19 15:07:13.253947+0800 Demo[49319:5169743] Start network Task task4
2017-12-19 15:07:13.253947+0800 Demo[49319:5169745] Start network Task task5
2017-12-19 15:07:13.254119+0800 Demo[49319:5169763] End networkTask task0
2017-12-19 15:07:13.254193+0800 Demo[49319:5169474] Start network Task task7
2017-12-19 15:07:13.254339+0800 Demo[49319:5169744] Start network Task task8
2017-12-19 15:07:13.254343+0800 Demo[49319:5169743] Start network Task task9
2017-12-19 15:07:14.258061+0800 Demo[49319:5169764] End networkTask task1
2017-12-19 15:07:15.258071+0800 Demo[49319:5169762] End networkTask task2
2017-12-19 15:07:16.258189+0800 Demo[49319:5169742] End networkTask task3
2017-12-19 15:07:17.258100+0800 Demo[49319:5169745] End networkTask task4
2017-12-19 15:07:18.258196+0800 Demo[49319:5169766] End networkTask task5
2017-12-19 15:07:19.258171+0800 Demo[49319:5169765] End networkTask task6
2017-12-19 15:07:20.259119+0800 Demo[49319:5169763] End networkTask task7
2017-12-19 15:07:21.258239+0800 Demo[49319:5169767] End networkTask task8
2017-12-19 15:07:22.258280+0800 Demo[49319:5169744] End networkTask task9
All network is done

自定义数据监听

当需要监听某个数据的变化,但不需要频繁的调用其对应的回调处理,可以使用 DispatchSourceUserData 进行监听,它会自动合并更改,并在队列空闲时进行回调,以节省 CPU 开销。

extension GCDKit {
convenience init(valueChanged: @escaping (T) -> ()) {
self.init()
userDataAddSource = DispatchSource.makeUserDataAddSource()
userDataAddSource?.setEventHandler(handler: { [weak self] in
guard let `self` = self else { return }
guard let value = self.value else { return }
valueChanged(value)
})
userDataAddSource?.resume()
}
func send(_ value: T) {
self.value = value
userDataAddSource?.add(data: 1)
}
}
=======================================================================
GCD = GCDKit<Int> { (value: Int) in
print(value)
}
let serialQueue = DispatchQueue(label: "com")
serialQueue.async {
for i in 1...1000{
self.GCD.send(i)
}
for i in 1000...9999 {
self.GCD.send(i)
}
}
=====================================================================
64
9999

监听进程

在 Mac 开发中,你可以监听其他进程的开启关闭情况:

let apps = NSRunningApplication.runningApplications(withBundleIdentifier: "com.apple.mail")
let processIdentifier = apps.first?.processIdentifier
let source = DispatchSource.makeProcessSource(identifier: pid, eventMask: .exit)
source.setEventHandler {
print("mail quit")
}
source.resume()
监听目录结构
let folder = try? FileManager.default.url(for: .documentDirectory,
in: .userDomainMask,
appropriateFor: nil,
create: false)
print(folder!.path)
let fd = open(folder!.path, O_CREAT, 0o644)
let queue = DispatchQueue(label: "m")
let source = DispatchSource.makeFileSystemObjectSource(fileDescriptor: fd,
eventMask: .all,
queue: queue)
source.setEventHandler {
print("folder changed")
}
source.resume()
let result = FileManager.default.createFile(atPath: folder!.path + "/abc", contents: nil, attributes: nil)
if result {
print(0)
}
else {
print(1)
}

线程安全

你可以在资源读写时对其所在线程进行一些限制,而不必使用线程锁,比如:
// .barrier 保证执行时会排斥其他的并发任务,一般用于写入事务,保证线程安全。

func barrierHandle(code: @escaping GCDKitHandleBlock) -> GCDKit {
let queue = DispatchQueue(label: "", attributes: .concurrent)
let workItem = DispatchWorkItem(flags: .barrier) {
code()
}
queue.async(group: group, execute: workItem)
return self
}
// 或者开启一个串行队列同步读写任务:
extension GCDKit {
var data: T? {
get {
return readWriteQueue.sync { value }
}
set {
readWriteQueue.sync { value = newValue }
}
}
}

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