c# - C#中 'volatile'关键字的用途是什么

Question

C# 中 volatile 关键字的用途是什么？

我需要在哪里使用这个关键字？

我看到了下面的语句，但是我无法理解为什么这里需要volatile？

internal volatile string UserName; 

Answer 1

请参阅规范的第 10.5.3 节，其中指出:

For non-volatile fields, optimization techniques that reorder instructions can lead to unexpected and unpredictable results in multi-threaded programs that access fields without synchronization such as that provided by the lock-statement (§8.12). These optimizations can be performed by the compiler, by the run-time system, or by hardware. For volatile fields, such reordering optimizations are restricted:

A read of a volatile field is called a volatile read. A volatile read has “acquire semantics”; that is, it is guaranteed to occur prior to any references to memory that occur after it in the instruction sequence.

A write of a volatile field is called a volatile write. A volatile write has “release semantics”; that is, it is guaranteed to happen after any memory references prior to the write instruction in the instruction sequence.

These restrictions ensure that all threads will observe volatile writes performed by any other thread in the order in which they were performed. A conforming implementation is not required to provide a single total ordering of volatile writes as seen from all threads of execution.

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