The memory requirements of individual data structures might get altered, depending upon the way packing is implemented in the compiler.

个别数据结构的内存需求可能会发生改变，这依赖于编译器中实现对齐的方式。

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Visibility is more subtle; it deals with the vagaries of memory caching and compiler optimizations.

可见性则更为微妙；它要对付内存缓存和编译器优化的各种反常行为。

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For example, a compiler may choose to optimize a loop index variable by storing it in a register, or the cache may delay flushing a new value of a variable to main memory until a more opportune time.

例如，编译器为了优化一个循环索引变量，可能会选择把它存储到一个寄存器中，或者缓存会延迟到一个更适合的时间，才把一个新的变量值存入主存。

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