GCD的特点
GCD会自动利用更多的CPU内核
GCD自动管理线程的生命周期（创建线程，调度任务，销毁线程等）
只需要告诉 GCD 想要如何执行什么任务，不需要编写任何线程管理代码
1.GCD 相关概念
任务（block）：就是需要执行的代码块，以block 的方式呈现。
同步（sync）： 在当前线程中执行，会阻塞当前线程，不会开启新的线程，所以只能一次执行一个任务，前一个任务执行完毕，当前线程才会执行后一个任务
异步（async）：不阻塞当前线程，由GCD 决定是否开启新的线程
队列（queue）:装载待执行任务的一种队形结构，和排队上车一样，先进先出。GCD 中有两种队列结构：串行队列和并发队列。
串行队列（serialQueue）：队列中的任务只能按顺序依次执行。
并发队列（conCurrentQueue）：队列中的任务可以多个同时执行，在async 下是真正的并发，在sync 下依然是串行，因为只有一条线程可用。
GCD是将要执行的代码加入队列中（串行队列或并发队列），然后指定运行方式（同步执行或异步执行）
2.创建队列
GCD 需要把代码块放到队列中，队列又分串行队列和并发队列。
第一个参数 label 是队列的标识符，可以为空，第二个attributes 是表示串行或者并发队列。默认为串行队列，.concurren 表示并发队列。
// 串行队列
let serialQueue = DispatchQueue(label: "dispatchSeralQueue")
//并发队列
let conCurrentQueue = DispatchQueue(label: "dispatchConcurrentQueue", attributes: .concurrent)
除了自定义的队列，系统还我们提供了两个队列
主队列，主队列是一个并发队列。
DispatchQueue.main.async {
}
全局队列，是一个并发队列
DispatchQueue.global().async {
}
3.GCD使用
队列和同步异步之间有多种组合方式
1.串行同步
2.串行异步
3.并发同步
4.并发异步
5.主队列同步
6.主队列异步
- 串行同步
let seralQueue = DispatchQueue(label: "dispatchSeralQueue")
seralQueue.sync {
for i in 0...3 {
debugPrint("queueTest seralQueue1: \(Thread.current), \(i)")
}
}
seralQueue.sync {
for i in 0...3 {
debugPrint("queueTest seralQueue2: \(Thread.current), \(i)")
}
}
"queueTest seralQueue1: <_NSMainThread: 0x600003db08c0>{number = 1, name = main}, 0"
"queueTest seralQueue1: <_NSMainThread: 0x600003db08c0>{number = 1, name = main}, 1"
"queueTest seralQueue1: <_NSMainThread: 0x600003db08c0>{number = 1, name = main}, 2"
"queueTest seralQueue1: <_NSMainThread: 0x600003db08c0>{number = 1, name = main}, 3"
"queueTest seralQueue2: <_NSMainThread: 0x600003db08c0>{number = 1, name = main}, 0"
"queueTest seralQueue2: <_NSMainThread: 0x600003db08c0>{number = 1, name = main}, 1"
"queueTest seralQueue2: <_NSMainThread: 0x600003db08c0>{number = 1, name = main}, 2"
"queueTest seralQueue2: <_NSMainThread: 0x600003db08c0>{number = 1, name = main}, 3"
结果，顺序执行，都在主线程
- 串行异步
let seralQueue = DispatchQueue(label: "dispatchSeralQueue")
seralQueue.async {
for i in 0...3 {
debugPrint("queueTest seralQueue1: \(Thread.current), \(i)")
}
}
seralQueue.async {
for i in 0...3 {
debugPrint("queueTest seralQueue2: \(Thread.current), \(i)")
}
}
"queueTest seralQueue1: <NSThread: 0x6000030d2c40>{number = 6, name = (null)}, 0"
"queueTest seralQueue1: <NSThread: 0x6000030d2c40>{number = 6, name = (null)}, 1"
"queueTest seralQueue1: <NSThread: 0x6000030d2c40>{number = 6, name = (null)}, 2"
"queueTest seralQueue1: <NSThread: 0x6000030d2c40>{number = 6, name = (null)}, 3"
"queueTest seralQueue2: <NSThread: 0x6000030d2c40>{number = 6, name = (null)}, 0"
"queueTest seralQueue2: <NSThread: 0x6000030d2c40>{number = 6, name = (null)}, 1"
"queueTest seralQueue2: <NSThread: 0x6000030d2c40>{number = 6, name = (null)}, 2"
"queueTest seralQueue2: <NSThread: 0x6000030d2c40>{number = 6, name = (null)}, 3"
结果不在主线程，但是依然是顺序执行
- 并发同步
let conCurrentQueue = DispatchQueue(label: "dispatchConcurrentQueue", attributes: .concurrent)
conCurrentQueue.sync {
for i in 0...3 {
debugPrint("queueTest conCurrentQueue1: \(Thread.current), \(i)")
}
}
conCurrentQueue.sync {
for i in 0...3 {
debugPrint("queueTest conCurrentQueue2: \(Thread.current), \(i)")
}
}
"queueTest conCurrentQueue1: <_NSMainThread: 0x600000648380>{number = 1, name = main}, 0"
"queueTest conCurrentQueue1: <_NSMainThread: 0x600000648380>{number = 1, name = main}, 1"
"queueTest conCurrentQueue1: <_NSMainThread: 0x600000648380>{number = 1, name = main}, 2"
"queueTest conCurrentQueue1: <_NSMainThread: 0x600000648380>{number = 1, name = main}, 3"
"queueTest conCurrentQueue2: <_NSMainThread: 0x600000648380>{number = 1, name = main}, 0"
"queueTest conCurrentQueue2: <_NSMainThread: 0x600000648380>{number = 1, name = main}, 1"
"queueTest conCurrentQueue2: <_NSMainThread: 0x600000648380>{number = 1, name = main}, 2"
"queueTest conCurrentQueue2: <_NSMainThread: 0x600000648380>{number = 1, name = main}, 3"
在主线程，顺序执行
- 并发异步
let conCurrentQueue = DispatchQueue(label: "dispatchConcurrentQueue", attributes: .concurrent)
conCurrentQueue.async {
for i in 0...3 {
debugPrint("queueTest conCurrentQueue1: \(Thread.current), \(i)")
}
}
conCurrentQueue.async {
for i in 0...3 {
debugPrint("queueTest conCurrentQueue2: \(Thread.current), \(i)")
}
}
"queueTest conCurrentQueue2: <NSThread: 0x600003bf2900>{number = 4, name = (null)}, 0"
"queueTest conCurrentQueue1: <NSThread: 0x600003b98240>{number = 6, name = (null)}, 0"
"queueTest conCurrentQueue2: <NSThread: 0x600003bf2900>{number = 4, name = (null)}, 1"
"queueTest conCurrentQueue1: <NSThread: 0x600003b98240>{number = 6, name = (null)}, 1"
"queueTest conCurrentQueue2: <NSThread: 0x600003bf2900>{number = 4, name = (null)}, 2"
"queueTest conCurrentQueue1: <NSThread: 0x600003b98240>{number = 6, name = (null)}, 2"
"queueTest conCurrentQueue2: <NSThread: 0x600003bf2900>{number = 4, name = (null)}, 3"
"queueTest conCurrentQueue1: <NSThread: 0x600003b98240>{number = 6, name = (null)}, 3"
任务同时进行，开启多个线程。
- 主队列同步和异步
//www.greatytc.com/p/253a3b572a0e，这篇文章已经记录。 - GCD 线程之间通信
DispatchQueue.global().async {
// 模拟耗时操作
Thread.sleep(forTimeInterval: 10)
DispatchQueue.main.async {
// 在主队列插入一个任务更新UI
}
}
-GCD 栅栏函数
当任务需要异步进行，但是这些任务需要分成两组来执行，第一组完成之后才能进行第二组的操作。这时候就用了到GCD的栅栏方法:
let dispathGroup = DispatchGroup()
let dispatchConcurrentQueue = DispatchQueue(label: "dispatchConcurrentQueue", attributes: .concurrent)
dispatchConcurrentQueue.async {
for i in 0...3 {
debugPrint("dispatchConcurrentQueue action1 \(i) at \(Thread.current)")
}
}
dispatchConcurrentQueue.async {
for i in 0...3 {
debugPrint("dispatchConcurrentQueue action2 \(i) at \(Thread.current)")
}
}
dispatchConcurrentQueue.async(group: dispathGroup, qos: .default, flags: .barrier) {
debugPrint("dispatchConcurrentQueue barrier")
}
dispatchConcurrentQueue.async {
for i in 0...3 {
debugPrint("dispatchConcurrentQueue action3 \(i) at \(Thread.current)")
}
}
dispatchConcurrentQueue.async {
for i in 0...3 {
debugPrint("dispatchConcurrentQueue action4 \(i) at \(Thread.current)")
}
}
"dispatchConcurrentQueue action2 0 at <NSThread: 0x6000002ab200>{number = 7, name = (null)}"
"dispatchConcurrentQueue action1 0 at <NSThread: 0x6000002aa580>{number = 4, name = (null)}"
"dispatchConcurrentQueue action2 1 at <NSThread: 0x6000002ab200>{number = 7, name = (null)}"
"dispatchConcurrentQueue action1 1 at <NSThread: 0x6000002aa580>{number = 4, name = (null)}"
"dispatchConcurrentQueue action2 2 at <NSThread: 0x6000002ab200>{number = 7, name = (null)}"
"dispatchConcurrentQueue action2 3 at <NSThread: 0x6000002ab200>{number = 7, name = (null)}"
"dispatchConcurrentQueue action1 2 at <NSThread: 0x6000002aa580>{number = 4, name = (null)}"
"dispatchConcurrentQueue action1 3 at <NSThread: 0x6000002aa580>{number = 4, name = (null)}"
"dispatchConcurrentQueue barrier"
"dispatchConcurrentQueue action3 0 at <NSThread: 0x6000002ab200>{number = 7, name = (null)}"
"dispatchConcurrentQueue action4 0 at <NSThread: 0x6000002aa580>{number = 4, name = (null)}"
"dispatchConcurrentQueue action3 1 at <NSThread: 0x6000002ab200>{number = 7, name = (null)}"
"dispatchConcurrentQueue action4 1 at <NSThread: 0x6000002aa580>{number = 4, name = (null)}"
"dispatchConcurrentQueue action3 2 at <NSThread: 0x6000002ab200>{number = 7, name = (null)}"
"dispatchConcurrentQueue action4 2 at <NSThread: 0x6000002aa580>{number = 4, name = (null)}"
"dispatchConcurrentQueue action3 3 at <NSThread: 0x6000002ab200>{number = 7, name = (null)}"
"dispatchConcurrentQueue action4 3 at <NSThread: 0x6000002aa580>{number = 4, name = (null)}"
- GCD 延迟执行
func dispatchAfter() {
debugPrint("\(Date())")
DispatchQueue.global().asyncAfter(deadline: .now() + 2) {
debugPrint("等了2 s\(Date())")
}
}
"2021-11-21 07:22:25 +0000"
"等了2 s2021-11-21 07:22:27 +0000"
- DispatchGroup
func dispatchGroupNotify() {
let dispatchGroup = DispatchGroup()
let seralQueue = DispatchQueue(label: "dispatchSeralSync")
seralQueue.async(group: dispatchGroup, execute: DispatchWorkItem(block: {
print("dispatchGroup do\(Thread.current)")
}))
seralQueue.async(group: dispatchGroup, execute: DispatchWorkItem(block: {
print("dispatchGroup do1\(Thread.current)")
}))
dispatchGroup.notify(queue: DispatchQueue.main, work: DispatchWorkItem(block: {
print("dispatchGroup.notify(queue: DispatchQueue.main\(Thread.current)")
}))
}
dispatchGroup do<NSThread: 0x6000016acbc0>{number = 4, name = (null)}
dispatchGroup do1<NSThread: 0x6000016acbc0>{number = 4, name = (null)}
dispatchGroup.notify(queue: DispatchQueue.main<_NSMainThread: 0x6000016e81c0>{number = 1, name = main}
