For a global declaration, you need to specify its type (that is, class name) and the identifier you want to use to refer to it (that is, variable name).

对于global声明，需要指定它的类型(即类名)和想要用于引用它的标识符(即变量名)。

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The variable name can be any normal identifier, like x.

其中的变量名可以是任何一般的标识符，如x。

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Here the self identifier declares a thread local variable time.

这里的self标识符声明一个线程局部变量time。

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