The control thread uses the CompareExchange(Int32, Int32, Int32) method to set the control variable to -1 (minus one), but only if the value is currently zero.

• 控制线程使用CompareExchange(Int32,Int32,Int32)方法将控制变量设置为-1(负一),但仅在此变量的当前值为零时才进行此设置。