C # : 如果从多个线程调用一个静态方法怎么办？

在我的应用程序中，我有一个静态方法，它可以同时从多个线程调用。我的数据有被混淆的危险吗？

在我的第一次尝试中，这个方法不是静态的，我创建了这个类的多个实例。在那种情况下，我的数据不知怎么搞混了。我不知道这是怎么发生的，因为它只是偶尔发生。我还在调试。 但是现在方法是静态的，到目前为止我没有问题。也许只是运气。我不确定。

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小开

Static methods should be fine for multiple threads.

Static data on the other hand could cause a problem because attempts to access the same data from different threads needs to be controlled to ensure that only one thread at a time is reading or writing the data.

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最佳答案

Variables declared inside methods (with the possible exception of "captured" variables) are isolated, so you won't get any inherent problems; however, if your static method accesses any shared state, all bets are off.

Examples of shared-state would be:

  • static fields
  • objects accessed from a common cache (non-serialized)
  • data obtained via the input parameters (and state on those objects), if it is possible that multiple threads are touching the same object(s)

If you have shared state, you must either:

  • take care not to mutate the state once it can be shared (better: use immutable objects to represent state, and take a snapshot of the state into a local variable - i.e. rather than reference whatever.SomeData repeatedly, you read whatever.SomeData once into a local variable, and then just use the variable - note that this only helps for immutable state!)
  • synchronize access to the data (all threads must synchronize) - either mutually exclusive or (more granular) reader/writer
小开

MSDN Always says :

Any public static (Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe.

Edit: As the guys here say, is not always the case, and clearly this applies to classes designed this way in the BCL, not to user created classes where this does not apply.

小开

Yes, it's just luck. ;)

It doesn't matter if the method is static or not, what matters is if the data is static or not.

If each thread has its own separate instance of the class with its own set of data, there is no risk of data being mixed up. If the data is static, there is only one set of data, and all threads share the same data, so there is no way to not mix it up.

When your data in separate instances still gets mixed up, it's most likely because the data is not really separate.


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