使用DispatchGroup进行快速线程处理 [英] Swift Threading with DispatchGroup

问题描述

我有以下代码，它使用DispatchGroup在任务完成时收到通知：

func getSomething(completion: ()->()) {
    completion()
}

func doSomeWork(completion: ()->()) {
    let myGroup: DispatchGroup = DispatchGroup()
    for _ in 0..<10 {
        myGroup.enter()
        getSomething {
            myGroup.leave()
        }
    }
    myGroup.notify(queue: DispatchQueue.main) { // this here is the key
        completion()
    }
}

DispatchQueue.global().async {
    print("We are doing background work")
    doSomeWork {
        print("We are done with the work - but on main thread now!!!")
    }
}

所以我的问题是，我在线程上调用某个函数，该函数有一个在某个固定队列上调用的完成。

我的选项是：

1. 检测Thread.isMainThread并在主队列或后台队列上通知
2. 为所有函数调用传递我们正在处理的队列 问题：这不是一个真正的智能设计模式
3. 处理此完成有固定队列的情况，然后再次手动调度

但我对任何选项都不满意...我不想收到这么多急件。

想象一下：

DispatchQueue.global().async {
    print("We are doing background work")
    doSomeWork {
        DispatchQueue.global().async {
            print("Now we are in background again")
        }
    }
}

这已经是一个级别3的闭包，使用起来并不是很好，特别是如果在后台异步调用中我们有另一个闭包或级别。

任何关于在这里做什么的帮助都是很棒的！谢谢您

推荐答案

问题是，我正在调用一个函数bla({//块代码 后台队列。Bla()在Main上调用完成处理程序 线程，由于分派组-Janosch Hübner

再次检查您的代码段

func doSomeWork(completion: ()->()) {
    let myGroup: DispatchGroup = DispatchGroup()
    for _ in 0..<10 {
        myGroup.enter()
        getSomething {
            myGroup.leave()
        }
    }
    myGroup.notify(queue: DispatchQueue.main) { // this here is the key
        completion()
    }
}

请看，因为getSomething是同步的，所以您可以简单地编写

func doSomeWork(completion: ()->()) {
    //let myGroup: DispatchGroup = DispatchGroup()
    for _ in 0..<10 {
        //myGroup.enter()
        getSomething {
            //myGroup.leave()
        }
    }
    //myGroup.notify(queue: DispatchQueue.main) { // this here is the key
        completion()
    //}
}

如果getSomething应该是异步的，请使用适当的API在某个组中运行它

func doSomeWork(completion: ()->()) {
    let myGroup: DispatchGroup = DispatchGroup()
    let queue = DispatchQueue.global()
    for _ in 0..<10 {
        //myGroup.enter()
        queue.async(group: myGroup) {
            getSomething {
            //myGroup.leave()
            }
        }
    }
    myGroup.notify(queue: DispatchQueue.main) { // this here is the key
        completion()
    }
}

与doSomeWork(completion: ()->())在同一线程(最好是同一队列)上运行completion()非常简单。

func doSomeWork(completion: ()->()) {
    let myGroup: DispatchGroup = DispatchGroup()
    let queue = DispatchQueue.global()
    for _ in 0..<10 {
        //myGroup.enter()
        queue.async(group: myGroup) {
            getSomething {
            //myGroup.leave()
            }
        }
    }
    //myGroup.notify(queue: DispatchQueue.main) { // this here is the key
        myGroup.wait()
        completion()
    //}
}

查看下一个游乐场页面，了解DispatchQueue.conCurentPerform如何更改您的设计以及Group通知的工作原理

import PlaygroundSupport
import Dispatch

PlaygroundPage.current.needsIndefiniteExecution = true

let q0 = DispatchQueue.global()
let q1 = DispatchQueue(label: "my_queue", attributes: .concurrent)
let g = DispatchGroup()
let g1 = DispatchGroup()
q0.async(group: g) {
    print("1    message from (q0): will do some concurrent jobs in the background")
    DispatchQueue.concurrentPerform(iterations: 5, execute: { (i) in
        sleep(1)
        print("	",i)
    })
    print("2    message from (q0): all concurrent jobs done")
    q0.async(group: g) {
        print("3    some other long time running on group...")
        sleep(3)
        print("3 ex")
    }
    q0.async(group: g1) {
        print("?    some other long time running on gifferent group...")
        sleep(4)
        print("? ex")
    }
    g1.notify(queue: .main, execute: {
        print("g1 empty")
    })
}
print("4    continue on main")
g.notify(queue: q1) {
    print("5    message from (q1): finished a")
    DispatchQueue.main.async {
        sleep(1)
        print("6    from main, should stop playground execution?")
        //PlaygroundPage.current.finishExecution()
    }
    print("7    message from (q1): finished b")

}
g1.notify(queue: .main) {
    print("8    from main, g1 is empty.")

}
print(" ... continue")

哪些打印在我的环境中

1    message from <OS_dispatch_queue_global: com.apple.root.default-qos>: will do some concurrent jobs in the background
4    continue on main
 ... continue
8    from main, g1 is empty.
     0
     2
     1
     3
     4
2    message from <OS_dispatch_queue_global: com.apple.root.default-qos>: all concurrent jobs done
3    some other long time running on group...
?    some other long time running on gifferent group...
3 ex
5    message from <OS_dispatch_queue_concurrent: my_queue>: finished a
7    message from <OS_dispatch_queue_concurrent: my_queue>: finished b
6    from main, should stop playground execution?
? ex
g1 empty

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