Is C#'s Copy-and-Check Event Handling Truly Thread-Safe?

C#incident and thread security: explore the controversial copy check mode

The thread security problem of the C#event has always attracted much attention, because the event entrustment may become NULL within the short period of time between checking the empty value and trigger the event. This has led to the advice of always creating a copy of the incident before checking the empty value and triggering the event.

Although this technology solves specific problems of the abnormal air reference, it fails to solve the potential competition conditions that allow the entrustment to allow events to be entrusted to first become NULL. As Jon Skeet, an JIT expert, CLR will not optimize the replication steps.

In the event of a trigger, another thread can cancel the subscription event, resulting in inconsistent execution processes. This behavior is particularly problematic when canceling the thread of subscribing to prevent calling events from processing procedures.

Relying on the replication check mode in the event to ensure that thread security has been criticized as "Cargo Cult Programming" (superstitious programming), it is just a copy of a practice without fully understanding its purpose or limitations. It covers potential competition conditions and provides a sense of false security.

.NET Framework did not provide a direct solution to alleviate this problem, but there are some technologies that can design thread security components. These technologies include the storage thread ID in the constructor to detect external interference, or to implement an explicit synchronization mechanism in the event access method method.

As an alternative method for copying and checking habits, the distribution of air entrustment to the event declaration can eliminate the demand for vacant values. However, it cannot solve the problem of competitive conditions.

In the end, providing thread security in the event -driven code requires a comprehensive method. It is necessary to solve the potential empty value problem and the problem of competitive conditions. It is not enough to copy the check mode, and it should be used with caution in multi -threaded environments.

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