DISPATCH_QUEUE_CONCURRENT和DISPATCH_QUEUE_SERIAL有什么区别

Question

我实现了以下类:

class GCDStudy {

    func asyncSerial(time:Double){
        let queue = dispatch_queue_create("DISPATCH_QUEUE_SERIAL",DISPATCH_QUEUE_SERIAL)

        dispatch_async(queue){

            var i:Double = 0
            while(i < 3){
                i++
                print("asyncSerial -wait:\(time)-\(i)")

            }
        }

    }

    func asyncConcurrent(time:Double){

        let queue = dispatch_queue_create("DISPATCH_QUEUE_CONCURRENT",DISPATCH_QUEUE_CONCURRENT)

        dispatch_async(queue){
            var i:Double = 0
            while(i < 3){
                i++
                print("asyncConcurrent -wait:\(time)-\(i)")
            }
        }
    }
}

并运行如下:

运行A:

gCDStudy = GCDStudy()
gCDStudy.asyncSerial(1)
gCDStudy.asyncSerial(2)

跑B

vgCDStudy2 = GCDStudy()
gCDStudy2.asyncConcurrent(1)
gCDStudy2.asyncConcurrent(2)

结果RunA:

asyncSerial -wait:1.0-1.0
asyncSerial -wait:2.0-1.0
asyncSerial -wait:1.0-2.0
asyncSerial -wait:2.0-2.0
asyncSerial -wait:1.0-3.0
asyncSerial -wait:2.0-3.0

RunB的结果:

asyncSerial -wait:1.0-1.0
asyncSerial -wait:2.0-1.0
asyncSerial -wait:1.0-2.0
asyncSerial -wait:2.0-2.0
asyncSerial -wait:1.0-3.0
asyncSerial -wait:2.0-3.0

这些结果是一样的,这些结果有什么不同？

有时这些结果是不同的.

谢谢

Answer 1

串行队列按照将它们添加到队列的顺序一次执行一个任务,而并发队列同时执行一个或多个任务.需要注意的一点是,即使对于并发队列,任务也会按照添加到队列的顺序启动.因此,在您的情况下,您可能会看到输出没有任何变化,因为print并发队列中的每个线程都会很快执行,因此它们看起来好像是按顺序执行的.

如果您希望看到差异,也许您可​​以尝试按如下方式更新代码:

class GCDStudy {

  func asyncSerial(time: Double) {
    let queue = dispatch_queue_create("DISPATCH_QUEUE_SERIAL", DISPATCH_QUEUE_SERIAL)

    for i in 0..<3 {
      dispatch_async(queue) {
        print("asyncSerial -wait:\(time)-\(i)")
      }
    }
  }

  func asyncConcurrent(time: Double) {
    let queue = dispatch_queue_create("DISPATCH_QUEUE_CONCURRENT", DISPATCH_QUEUE_CONCURRENT)

    for i in 0..<3 {
      dispatch_async(queue) {
        print("asyncConcurrent -wait:\(time)-\(i)")
      }
    }
  }
}