Specifies that each thread should have its own instance of a variable, and that the variable should be initialized with the value of the variable, because it exists before the parallel construct.
Specifies that each thread should have its own instance of a variable, and that the variable should be initialized with the value of the variable, because it exists before the parallel construct.
让每个执行绪中，都有一份变数的复本，以免互相干扰；而起始值则会是开始平行化之前的变数值。