开头

• 这是分篇章，整篇请看零基础iOS开发学习日记

Swift版的GCD

• 因为GCD在Swift中还是变化挺多的，就另外整理一下

并发队列

• 异步执行

let concurrent = DispatchQueue(label: "concurrent", attributes:.concurrent)
for i in 0..<10 {
    concurrent.async {
        print("\(i) ------ \(Thread.current)")
    }
}

• 同步执行

let concurrent = DispatchQueue(label: "concurrent")
for i in 0..<10 {
    concurrent.sync {
        print("\(i) ------ \(Thread.current)")
    }
}

• 简化，第二个参数设置了是并发队列，不设置默认是串行队列

DispatchQueue(label: "concurrent", attributes: .concurrent).async {
    print("\(i) ------ \(Thread.current)")
}

串行队列

• 异步执行

let serial = DispatchQueue(label: "serial")
for i in 0..<10 {
    serial.async {
        print("\(i) ------ \(Thread.current)")
    }
    
}

• 同步执行

let serial = DispatchQueue(label: "serial")
for i in 0..<10 {
    serial.sync {
        print("\(i) ------ \(Thread.current)")
    }
    
}

主队列与全局队列

• 主队列

for i in 0..<10 {
    DispatchQueue.main.async {
        print("\(i) ------ \(Thread.current)")
    }
}

• 全局队列

let global = DispatchQueue.global()
for i in 0..<10 {
    global.async {
        print("\(i) ------ \(Thread.current)")
    }
    
}

let global = DispatchQueue.global()
for i in 0..<10 {
    global.sync {
        print("\(i) ------ \(Thread.current)")
    }
    
}

调度组

• notify

let group = DispatchGroup()
let concurrent = DispatchQueue(label: "concurrent", attributes: .concurrent)
concurrent.async(group: group) {
    Thread.sleep(forTimeInterval: 5)
    print("1-----\(Thread.current)")
}
concurrent.async(group: group) {
        Thread.sleep(forTimeInterval: 5)
        print("2-----\(Thread.current)")
    }
group.notify(queue: DispatchQueue.main) {
    print("finish --- \(Thread.current)")
    print("group end")
}

• wait

group.wait()
print("group end")

• 原理

let group = DispatchGroup()
let concurrent = DispatchQueue(label: "concurrent", attributes: .concurrent)

group.enter()
concurrent.async {
    Thread.sleep(forTimeInterval: 5)
    print("1-----\(Thread.current)")
    group.leave()
}
group.enter()
concurrent.async {
    Thread.sleep(forTimeInterval: 5)
    print("2-----\(Thread.current)")
    group.leave()
}

group.wait()
print("group end")

DispatchWorkItem

• DispatchWorkItem一段预执行的代码

let workItme = DispatchWorkItem {
    Thread.sleep(forTimeInterval: 5)
    print("workItme ----- \(Thread.current)")
    
}
concurrent.async(execute: workItme)

DispatchQueue参数详解

DispatchQueue(label: String,  //队列名
qos: DispatchQoS,  //服务优先级
attributes: DispatchQueue.Attributes, //队列类型，不设置时为串行队列；concurrent为并发队列；initiallyInactive需要队列的activate手动触发 
autoreleaseFrequency: DispatchQueue.AutoreleaseFrequency, //自动释放频率，inherit继承目标队列；workItem自动释放池；never不会创建自动释放池
target: DispatchQueue?) //设置了队列的目标队列

• initiallyInactive

let queue = DispatchQueue(label: "concurrent", attributes: [.concurrent, .initiallyInactive])
queue.async {
    print(Thread.current)
}
queue.activate()