Playground——DispatchQueue和DispatchSemaphore的关系
Playground - The relationship between DispatchQueue and DispatchSemaphore
我对 DispatchQueue 感到困惑,DispatchSemaphore.Like 以下示例:
let semaphore : DispatchSemaphore = DispatchSemaphore(value:1)
for i in 1...40 {
DispatchQueue.global().async{
semaphore.wait()
NSLog("......1-%d",i)
semaphore.signal()
}
}
我认为它应该打印 1...40,实际上它只打印了大约 25,结果如下:
2016-11-18 19:05:38.786 MyPlayground[7436:495171] ......1-1
2016-11-18 19:05:38.787 MyPlayground[7436:495175] ......1-2
......
2016-11-18 19:05:38.797 MyPlayground[7436:495258] ......1-23
2016-11-18 19:05:38.797 MyPlayground[7436:495244] ......1-24
这是什么原因?
因为你是 运行 它是异步的,所以 Playground 在所有 40 次迭代完成之前完成。将这两行添加到代码的开头或结尾:
import PlaygroundSupport
PlaygroundPage.current.needsIndefiniteExecution = true
我对 DispatchQueue 感到困惑,DispatchSemaphore.Like 以下示例:
let semaphore : DispatchSemaphore = DispatchSemaphore(value:1)
for i in 1...40 {
DispatchQueue.global().async{
semaphore.wait()
NSLog("......1-%d",i)
semaphore.signal()
}
}
我认为它应该打印 1...40,实际上它只打印了大约 25,结果如下:
2016-11-18 19:05:38.786 MyPlayground[7436:495171] ......1-1
2016-11-18 19:05:38.787 MyPlayground[7436:495175] ......1-2
......
2016-11-18 19:05:38.797 MyPlayground[7436:495258] ......1-23
2016-11-18 19:05:38.797 MyPlayground[7436:495244] ......1-24
这是什么原因?
因为你是 运行 它是异步的,所以 Playground 在所有 40 次迭代完成之前完成。将这两行添加到代码的开头或结尾:
import PlaygroundSupport
PlaygroundPage.current.needsIndefiniteExecution = true