参考文章：
iOS多线程--彻底学会多线程之『GCD』
Swift 3.0 GCD和DispatchQueue 使用解析
这哥们已经写得很好了，代码这东西，不敲一下，总觉得就不是自己的。再者，swift GDC的接口真是改得那个揪心啊~！
并行队列+同步执行
不会创建新的线程，而是在当前线程立即执行
let queue = DispatchQueue.init(label: "com.bear.queue", attributes: .concurrent)
queue.sync {
print("1-----\(Thread.current)")
}
queue.sync {
print("2-----\(Thread.current)")
}
queue.sync {
print("3-----\(Thread.current)")
}
queue.sync {
print("4-----\(Thread.current)")
}
output:
1-----{number = 1, name = main}
2-----{number = 1, name = main}
3-----{number = 1, name = main}
4-----{number = 1, name = main}
并行队列+异步执行
会创建新的线程
let queue = DispatchQueue.init(label: "com.bear.queue", attributes: .concurrent)
let sem = DispatchSemaphore.init(value: 0)
queue.async {
print("1-----\(Thread.current)")
}
queue.async {
print("2-----\(Thread.current)")
}
queue.async {
print("3-----\(Thread.current)")
}
queue.async {
print("4-----\(Thread.current)")
}
output:
3-----{number = 3, name = (null)}
2-----{number = 4, name = (null)}
1-----{number = 2, name = (null)}
4-----{number = 5, name = (null)}
串行队列+异步执行
let queue = DispatchQueue.init(label: "com.bear.queue")
let sem = DispatchSemaphore.init(value: 0)
queue.async {
print("1-----\(Thread.current)")
}
queue.async {
print("2-----\(Thread.current)")
}
queue.async {
print("3-----\(Thread.current)")
}
queue.async {
print("4-----\(Thread.current)")
}
output:
1-----{number = 2, name = (null)}
2-----{number = 2, name = (null)}
3-----{number = 2, name = (null)}
4-----{number = 2, name = (null)}
串行队列+同步执行
let queue = DispatchQueue.init(label: "com.bear.queue")
queue.sync {
print("1-----\(Thread.current)")
}
queue.sync {
print("2-----\(Thread.current)")
}
queue.sync {
print("3-----\(Thread.current)")
}
queue.sync {
print("4-----\(Thread.current)")
}
output:
1-----{number = 1, name = main}
2-----{number = 1, name = main}
3-----{number = 1, name = main}
4-----{number = 1, name = main}
主队列+同步执行（这个会死锁）
主队列+异步执行
虽然是异步的，但由于分配到主队列中，所以不会创建新的线程。
DispatchQueue.main.async {
print("1-----\(Thread.current)")
}
DispatchQueue.main.async {
print("2-----\(Thread.current)")
}
DispatchQueue.main.async {
print("3-----\(Thread.current)")
}
DispatchQueue.main.async {
print("4-----\(Thread.current)")
}
output:
1-----{number = 1, name = main}
2-----{number = 1, name = main}
3-----{number = 1, name = main}
4-----{number = 1, name = main}
异步一般情况下会创建新的线程来执行任务。
同步队列需要停止当前正在执行的任务立即执行任务
串行队列就是一个接一个的执行
并发队列就是一起塞进队列中，何时执行，创建多少线程执行收系统决定
主队列中的异步任务不会创建新的线程（是不是可以说主队列只一个主线程）
线程间通信
说得好高大上，其实就是GDC嵌套。
let queue = DispatchQueue.init(label: "com.bear.queue")
queue.async {
print("\(Thread.current)")
DispatchQueue.main.async {
print("\(Thread.current)")
}
}
任务分组
当多个任务进行并发异步执行的时候，任务的执行顺序是随机的。此时可以通过barrier将任务进行分组。分组后组的执行顺序按代码顺序执行。而组内的顺序依旧是随机的。
let queue = DispatchQueue.init(label: "com.bear.thread", attributes: .concurrent)
queue.async {
print("1----\(Thread.current)")
}
queue.async {
print("2----\(Thread.current)")
}
queue.async {
print("3----\(Thread.current)")
}
queue.async {
print("1----\(Thread.current)")
}
queue.async {
print("2----\(Thread.current)")
}
queue.async {
print("3----\(Thread.current)")
}
queue.async(flags: .barrier) {
print("----barrier----")
}
queue.async {
print("4----\(Thread.current)")
}
queue.async {
print("5----\(Thread.current)")
}
queue.async {
print("4----\(Thread.current)")
}
queue.async {
print("5----\(Thread.current)")
}
queue.async(flags: .barrier) {
print("----barrier----")
}
queue.async {
print("6----\(Thread.current)")
}
queue.async {
print("7----\(Thread.current)")
}
queue.async {
print("6----\(Thread.current)")
}
queue.async {
print("7----\(Thread.current)")
}
output:
1----{number = 3, name = (null)}
3----{number = 6, name = (null)}
2----{number = 5, name = (null)}
1----{number = 4, name = (null)}
2----{number = 3, name = (null)}
3----{number = 6, name = (null)}
----barrier----
4----{number = 6, name = (null)}
5----{number = 3, name = (null)}
4----{number = 6, name = (null)}
5----{number = 4, name = (null)}
----barrier----
6----{number = 4, name = (null)}
6----{number = 4, name = (null)}
7----{number = 4, name = (null)}
7----{number = 6, name = (null)}
延时任务
let queue = DispatchQueue.init(label: "com.bear.thread", attributes: .concurrent)
queue.asyncAfter(deadline: DispatchTime.now() + 3) {
print("hello")
}
Group(等待任务结束后执行)
let queue = DispatchQueue.init(label: "com.bear.thread", attributes: .concurrent)
let group = DispatchGroup.init()
let sem = DispatchSemaphore.init(value: 0)
queue.async(group: group) {
sem.signal()
print("group 1")
}
queue.async(group: group) {
sem.signal()
print("group 2")
}
queue.async(group: group) {
sem.signal()
print("group 3")
}
queue.async(group: group) {
sem.signal()
print("group 4")
}
group.notify(queue: queue) {
sem.wait()
sem.wait()
sem.wait()
sem.wait()
print("end")
}
output:
group 1
group 4
group 3
group 2
end
DispatchWorkItem
类似dispatch_block_t
let queue = DispatchQueue.init(label: "com.bear.thread", attributes: .concurrent)
let dispatchWorkItem : DispatchWorkItem = DispatchWorkItem.init {
print("hello")
}
dispatchWorkItem.perform()
dispatchWorkItem.notify(queue: queue) {
print("world")
}
DispatchSource
这个和Timer有啥区别呢？-。-
func dispatchSource() {
var count = 0
let queue = DispatchQueue.init(label: "com.bear.thread", attributes: .concurrent)
let timer = DispatchSource.makeTimerSource(queue: queue)
timer.setEventHandler(handler: DispatchWorkItem{
print("hello world")
count += 1
if count >= 5 {
timer.cancel()
}
})
// timer.scheduleOneshot(deadline: .now())
timer.scheduleRepeating(deadline: .now() + 3, interval: .seconds(1))
timer.resume()
}