全局并发队（Global Queue）

• 老版gcd有四种：high，default，low，background，

  优先级为：high>default>low>background

• 新版gcd有六种：background，utility，default，userInitiated，userInteractive，unspecified

  优先级为：userInteractive>default>unspecified>userInitiated>utility>background

  测试代码如下：

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 for i in 1...3 {
        DispatchQueue.global(qos: DispatchQoS.QoSClass.default).async {
            NSLog("DispatchQoS.QoSClass.default, %d", i)
        }

        DispatchQueue.global(qos: DispatchQoS.QoSClass.background).async {
            NSLog("DispatchQoS.QoSClass.background, %d", i)
        }

        DispatchQueue.global(qos: DispatchQoS.QoSClass.unspecified).async {
            NSLog("DispatchQoS.QoSClass.unspecified, %d", i)
        }

        DispatchQueue.global(qos: DispatchQoS.QoSClass.userInitiated).async {
            NSLog("DispatchQoS.QoSClass.userInitiated, %d", i)
        }

        DispatchQueue.global(qos: DispatchQoS.QoSClass.userInteractive).async {
            NSLog("DispatchQoS.QoSClass.userInteractive, %d", i)
        }

        DispatchQueue.global(qos: DispatchQoS.QoSClass.utility).async {
            NSLog("DispatchQoS.QoSClass.utility, %d", i)
        }
    }

输出日志：

“`objective-c

2018-07-24 15:04:12.619688+0800 YKBaseSwiftFramework[8252:505814] DispatchQoS.QoSClass.userInteractive, 3 2018-07-24 15:04:12.619688+0800 YKBaseSwiftFramework[8252:505813] DispatchQoS.QoSClass.userInteractive, 2 2018-07-24 15:04:12.619688+0800 YKBaseSwiftFramework[8252:505825] DispatchQoS.QoSClass.userInteractive, 1 2018-07-24 15:04:12.619716+0800 YKBaseSwiftFramework[8252:505820] DispatchQoS.QoSClass.default, 1 2018-07-24 15:04:12.619735+0800 YKBaseSwiftFramework[8252:505815] DispatchQoS.QoSClass.unspecified, 1 2018-07-24 15:04:12.619741+0800 YKBaseSwiftFramework[8252:505828] DispatchQoS.QoSClass.userInitiated, 1 2018-07-24 15:04:12.620001+0800 YKBaseSwiftFramework[8252:505830] DispatchQoS.QoSClass.default, 2 2018-07-24 15:04:12.620003+0800 YKBaseSwiftFramework[8252:505814] DispatchQoS.QoSClass.unspecified, 2 2018-07-24 15:04:12.620065+0800 YKBaseSwiftFramework[8252:505831] DispatchQoS.QoSClass.userInitiated, 2 2018-07-24 15:04:12.620101+0800 YKBaseSwiftFramework[8252:505832] DispatchQoS.QoSClass.default, 3 2018-07-24 15:04:12.620122+0800 YKBaseSwiftFramework[8252:505834] DispatchQoS.QoSClass.userInitiated, 3 2018-07-24 15:04:12.620133+0800 YKBaseSwiftFramework[8252:505833] DispatchQoS.QoSClass.unspecified, 3 2018-07-24 15:04:12.620143+0800 YKBaseSwiftFramework[8252:505827] DispatchQoS.QoSClass.utility, 1 2018-07-24 15:04:12.620286+0800 YKBaseSwiftFramework[8252:505829] DispatchQoS.QoSClass.utility, 2 2018-07-24 15:04:12.620343+0800 YKBaseSwiftFramework[8252:505835] DispatchQoS.QoSClass.utility, 3 2018-07-24 15:04:12.622419+0800 YKBaseSwiftFramework[8252:505824] DispatchQoS.QoSClass.background, 1 2018-07-24 15:04:12.622904+0800 YKBaseSwiftFramework[8252:505832] DispatchQoS.QoSClass.background, 2 2018-07-24 15:04:12.622998+0800 YKBaseSwiftFramework[8252:505831] DispatchQoS.QoSClass.background, 3

“`