用例子看Swift4的GCD
关于GCD基础知识的文章很多,但很多都停留在iOS早期版本的状态,随着iOS的升级GCD的使用也随之升级了,下面举了很多例子来看一看。
1、串行队列使用同步运行
////1、普通队列同步运行 let queue = DispatchQueue(label:"com.test") queue.sync{ for _ in 0..<6 { print("aaaaaaa\(Thread.current)") } } for _ in 0..<6 { print("bbbbbbb\(Thread.current)") }
运行结果:
aaaaaaa<NSThread: 0x6040002608c0>{number = 1, name = main}
aaaaaaa<NSThread: 0x6040002608c0>{number = 1, name = main}
aaaaaaa<NSThread: 0x6040002608c0>{number = 1, name = main}
aaaaaaa<NSThread: 0x6040002608c0>{number = 1, name = main}
aaaaaaa<NSThread: 0x6040002608c0>{number = 1, name = main}
aaaaaaa<NSThread: 0x6040002608c0>{number = 1, name = main}
bbbbbbb<NSThread: 0x6040002608c0>{number = 1, name = main}
bbbbbbb<NSThread: 0x6040002608c0>{number = 1, name = main}
bbbbbbb<NSThread: 0x6040002608c0>{number = 1, name = main}
bbbbbbb<NSThread: 0x6040002608c0>{number = 1, name = main}
bbbbbbb<NSThread: 0x6040002608c0>{number = 1, name = main}
bbbbbbb<NSThread: 0x6040002608c0>{number = 1, name = main}
结果分析:
串行队形完全阻断了主线程的运行,都使用main线程,这种写法是完全没有意义的。
2、串行队列使用异步运行
//2、普通队列异步运行 let queue = DispatchQueue(label:"com.test") queue.async{ for _ in 0..<6 { print("aaaaaaa\(Thread.current)") } } for _ in 0..<6 { print("bbbbbbb\(Thread.current)") }
运行结果:
bbbbbbb<NSThread: 0x604000066580>{number = 1, name = main}
aaaaaaa<NSThread: 0x600000071680>{number = 3, name = (null)}
aaaaaaa<NSThread: 0x600000071680>{number = 3, name = (null)}
bbbbbbb<NSThread: 0x604000066580>{number = 1, name = main}
aaaaaaa<NSThread: 0x600000071680>{number = 3, name = (null)}
bbbbbbb<NSThread: 0x604000066580>{number = 1, name = main}
bbbbbbb<NSThread: 0x604000066580>{number = 1, name = main}
bbbbbbb<NSThread: 0x604000066580>{number = 1, name = main}
bbbbbbb<NSThread: 0x604000066580>{number = 1, name = main}
aaaaaaa<NSThread: 0x600000071680>{number = 3, name = (null)}
aaaaaaa<NSThread: 0x600000071680>{number = 3, name = (null)}
aaaaaaa<NSThread: 0x600000071680>{number = 3, name = (null)}
运行结果分析:
串行队列任务与主线程并行,串行队列使用了新的线程3,感觉上就像自己启了一个线程在做事情,使用DispatchQueue会方便很多。
3、串行队列多次运行
//3、普通队列异步运行多次 let queue = DispatchQueue(label:"com.test",qos:DispatchQoS.unspecified) queue.async{ for _ in 0..<6 { print("aaaaaaa\(Thread.current)") } } queue.async{ for _ in 0..<6 { print("cccccc\(Thread.current)") } } for _ in 0..<6 { print("bbbbbbb\(Thread.current)") }
运行结果:
bbbbbbb<NSThread: 0x60400007cc40>{number = 1, name = main}
aaaaaaa<NSThread: 0x604000264a80>{number = 3, name = (null)}
aaaaaaa<NSThread: 0x604000264a80>{number = 3, name = (null)}
bbbbbbb<NSThread: 0x60400007cc40>{number = 1, name = main}
bbbbbbb<NSThread: 0x60400007cc40>{number = 1, name = main}
aaaaaaa<NSThread: 0x604000264a80>{number = 3, name = (null)}
bbbbbbb<NSThread: 0x60400007cc40>{number = 1, name = main}
aaaaaaa<NSThread: 0x604000264a80>{number = 3, name = (null)}
bbbbbbb<NSThread: 0x60400007cc40>{number = 1, name = main}
bbbbbbb<NSThread: 0x60400007cc40>{number = 1, name = main}
aaaaaaa<NSThread: 0x604000264a80>{number = 3, name = (null)}
aaaaaaa<NSThread: 0x604000264a80>{number = 3, name = (null)}
cccccc<NSThread: 0x604000264a80>{number = 3, name = (null)}
cccccc<NSThread: 0x604000264a80>{number = 3, name = (null)}
cccccc<NSThread: 0x604000264a80>{number = 3, name = (null)}
cccccc<NSThread: 0x604000264a80>{number = 3, name = (null)}
cccccc<NSThread: 0x604000264a80>{number = 3, name = (null)}
cccccc<NSThread: 0x604000264a80>{number = 3, name = (null)}
运行结果分析:
队形中任务与主线程并行且使用了新的线程3,这里可以看处理,串行队列只有等第一个任务运行完才执行第二个(所以aaaaaa打印完,才有cccccc),这里例子很适合做并发中互斥操作,不使用锁。
4、并行队列异步运行多次
//4、并行队列异步运行多次 let queue = DispatchQueue(label:"com.test",qos:DispatchQoS.unspecified,attributes:.concurrent) queue.async{ for _ in 0..<6 { print("aaaaaaa\(Thread.current)") } } queue.async{ for _ in 0..<6 { print("cccccc\(Thread.current)") } } for _ in 0..<6 { print("bbbbbbb\(Thread.current)") }
运行结果:
bbbbbbb<NSThread: 0x604000079c00>{number = 1, name = main}
aaaaaaa<NSThread: 0x6040002657c0>{number = 4, name = (null)}
cccccc<NSThread: 0x600000267380>{number = 3, name = (null)}
bbbbbbb<NSThread: 0x604000079c00>{number = 1, name = main}
aaaaaaa<NSThread: 0x6040002657c0>{number = 4, name = (null)}
cccccc<NSThread: 0x600000267380>{number = 3, name = (null)}
bbbbbbb<NSThread: 0x604000079c00>{number = 1, name = main}
cccccc<NSThread: 0x600000267380>{number = 3, name = (null)}
bbbbbbb<NSThread: 0x604000079c00>{number = 1, name = main}
aaaaaaa<NSThread: 0x6040002657c0>{number = 4, name = (null)}
bbbbbbb<NSThread: 0x604000079c00>{number = 1, name = main}
bbbbbbb<NSThread: 0x604000079c00>{number = 1, name = main}
cccccc<NSThread: 0x600000267380>{number = 3, name = (null)}
cccccc<NSThread: 0x600000267380>{number = 3, name = (null)}
aaaaaaa<NSThread: 0x6040002657c0>{number = 4, name = (null)}
cccccc<NSThread: 0x600000267380>{number = 3, name = (null)}
aaaaaaa<NSThread: 0x6040002657c0>{number = 4, name = (null)}
aaaaaaa<NSThread: 0x6040002657c0>{number = 4, name = (null)}
运行结果分析:
并行队列的2个任务与主线程同时运行,并行队列中任务分别使用线程3和线程4,这是一个并发的场景,比如我们一边加载不同图片一边不会影响UI的响应;这里也可以看出串行队列与并行队列的不同之处。
5、多个串行队列异步运行
let queue = DispatchQueue(label:"com.test",qos:DispatchQoS.unspecified) let queue2 = DispatchQueue(label:"com.test",qos:DispatchQoS.userInteractive) queue.async{ for _ in 0..<16 { print("aaaaaaa\(Thread.current)") } } queue2.async{ for _ in 0..<16 { print("cccccc\(Thread.current)") } }
运行结果:
cccccc<NSThread: 0x60400006ec80>{number = 3, name = (null)}
aaaaaaa<NSThread: 0x60400006ecc0>{number = 4, name = (null)}
cccccc<NSThread: 0x60400006ec80>{number = 3, name = (null)}
aaaaaaa<NSThread: 0x60400006ecc0>{number = 4, name = (null)}
cccccc<NSThread: 0x60400006ec80>{number = 3, name = (null)}
aaaaaaa<NSThread: 0x60400006ecc0>{number = 4, name = (null)}
cccccc<NSThread: 0x60400006ec80>{number = 3, name = (null)}
aaaaaaa<NSThread: 0x60400006ecc0>{number = 4, name = (null)}
cccccc<NSThread: 0x60400006ec80>{number = 3, name = (null)}
aaaaaaa<NSThread: 0x60400006ecc0>{number = 4, name = (null)}
cccccc<NSThread: 0x60400006ec80>{number = 3, name = (null)}
cccccc<NSThread: 0x60400006ec80>{number = 3, name = (null)}
aaaaaaa<NSThread: 0x60400006ecc0>{number = 4, name = (null)}
cccccc<NSThread: 0x60400006ec80>{number = 3, name = (null)}
cccccc<NSThread: 0x60400006ec80>{number = 3, name = (null)}
aaaaaaa<NSThread: 0x60400006ecc0>{number = 4, name = (null)}
cccccc<NSThread: 0x60400006ec80>{number = 3, name = (null)}
aaaaaaa<NSThread: 0x60400006ecc0>{number = 4, name = (null)}
cccccc<NSThread: 0x60400006ec80>{number = 3, name = (null)}
aaaaaaa<NSThread: 0x60400006ecc0>{number = 4, name = (null)}
cccccc<NSThread: 0x60400006ec80>{number = 3, name = (null)}
cccccc<NSThread: 0x60400006ec80>{number = 3, name = (null)}
aaaaaaa<NSThread: 0x60400006ecc0>{number = 4, name = (null)}
cccccc<NSThread: 0x60400006ec80>{number = 3, name = (null)}
aaaaaaa<NSThread: 0x60400006ecc0>{number = 4, name = (null)}
cccccc<NSThread: 0x60400006ec80>{number = 3, name = (null)}
aaaaaaa<NSThread: 0x60400006ecc0>{number = 4, name = (null)}
cccccc<NSThread: 0x60400006ec80>{number = 3, name = (null)}
aaaaaaa<NSThread: 0x60400006ecc0>{number = 4, name = (null)}
aaaaaaa<NSThread: 0x60400006ecc0>{number = 4, name = (null)}
aaaaaaa<NSThread: 0x60400006ecc0>{number = 4, name = (null)}
aaaaaaa<NSThread: 0x60400006ecc0>{number = 4, name = (null)}
运行结果分析:
例子中队列2的优先级比队列1高,所以cccccc在aaaaaa之前打印完,2个不同的串行队列使用不同的线程3和4,并行队列的优先级比较也是一样的结果,这里就不发例子
6、使用DispatchGroup做任务依赖
queue先做一个短任务,并行的queue2做一个长任务,等2个任务都做完group通知queue接着做任务,任务C依赖与任务A和任务B同时完成。
let queue = DispatchQueue(label:"com.test",qos:DispatchQoS.unspecified) let queue2 = DispatchQueue(label:"com.test",qos:DispatchQoS.userInteractive) let group = DispatchGroup() queue.async(group: group, execute: { for _ in 0..<3 { print("aaaaaaa\(Thread.current)") } }) queue2.async(group: group, execute: { for _ in 0..<6 { print("bbbbb\(Thread.current)") } }) //执行完上面的两个耗时操作, 回到queue队列中执行下一步的任务 group.notify(queue: queue) { print("回到queue该队列中执行") for _ in 0..<3 { print("bbbbb\(Thread.current)") } }
运行结果:
bbbbb<NSThread: 0x604000078540>{number = 3, name = (null)}
aaaaaaa<NSThread: 0x604000078580>{number = 4, name = (null)}
bbbbb<NSThread: 0x604000078540>{number = 3, name = (null)}
aaaaaaa<NSThread: 0x604000078580>{number = 4, name = (null)}
bbbbb<NSThread: 0x604000078540>{number = 3, name = (null)}
aaaaaaa<NSThread: 0x604000078580>{number = 4, name = (null)}
bbbbb<NSThread: 0x604000078540>{number = 3, name = (null)}
bbbbb<NSThread: 0x604000078540>{number = 3, name = (null)}
bbbbb<NSThread: 0x604000078540>{number = 3, name = (null)}
回到queue该队列中执行
cccccc<NSThread: 0x604000078580>{number = 4, name = (null)}
cccccc<NSThread: 0x604000078580>{number = 4, name = (null)}
cccccc<NSThread: 0x604000078580>{number = 4, name = (null)}
运行结果分析:
2任务分别运行做线程3和4,等他们都做完再到queue中打印cccccc
7、使用DispatchGroup做任务等待
queue和queue2是2个并行的队列,queue2中sleep(UInt32(3))可以让queue2超时
let queue = DispatchQueue(label:"com.test",qos:DispatchQoS.unspecified) let queue2 = DispatchQueue(label:"com.test",qos:DispatchQoS.userInteractive) let group = DispatchGroup() queue.async(group: group, execute: { for _ in 0..<3 { print("aaaaaaa\(Thread.current)") } }) queue2.async(group: group, execute: { for _ in 0..<6 { print("bbbbb\(Thread.current)") } //sleep(UInt32(3)) }) //等待上面任务执行,会阻塞当前线程,超时就执行下面的,上面的继续执行。可以无限等待 .distantFuture let result:DispatchTimeoutResult = group.wait(timeout: .now() + 2.0) switch result { case .success: print("不超时, 上面的两个任务都执行完") case .timedOut: print("超时了, 上面的任务还没执行完执行这了") } print("接下来的操作")
打开sleep(UInt32(3)) 的结果:
aaaaaaa<NSThread: 0x604000273140>{number = 4, name = (null)}
bbbbb<NSThread: 0x6000004703c0>{number = 3, name = (null)}
aaaaaaa<NSThread: 0x604000273140>{number = 4, name = (null)}
bbbbb<NSThread: 0x6000004703c0>{number = 3, name = (null)}
bbbbb<NSThread: 0x6000004703c0>{number = 3, name = (null)}
bbbbb<NSThread: 0x6000004703c0>{number = 3, name = (null)}
aaaaaaa<NSThread: 0x604000273140>{number = 4, name = (null)}
bbbbb<NSThread: 0x6000004703c0>{number = 3, name = (null)}
bbbbb<NSThread: 0x6000004703c0>{number = 3, name = (null)}
超时了, 上面的任务还没执行完执行这了
接下来的操作
注解sleep(UInt32(3))结果:
bbbbb<NSThread: 0x604000273280>{number = 3, name = (null)}
aaaaaaa<NSThread: 0x600000278e00>{number = 4, name = (null)}
aaaaaaa<NSThread: 0x600000278e00>{number = 4, name = (null)}
bbbbb<NSThread: 0x604000273280>{number = 3, name = (null)}
aaaaaaa<NSThread: 0x600000278e00>{number = 4, name = (null)}
bbbbb<NSThread: 0x604000273280>{number = 3, name = (null)}
bbbbb<NSThread: 0x604000273280>{number = 3, name = (null)}
bbbbb<NSThread: 0x604000273280>{number = 3, name = (null)}
bbbbb<NSThread: 0x604000273280>{number = 3, name = (null)}
不超时, 上面的两个任务都执行完
接下来的操作
结果分析:
可以用Group的wait方法来做超时判断。
ps:例子多了点,都是一个一个字码的,系统对学习Swift的GCD有用。