Synchronizing access to shared resources

When you have multiple threads executing at the same time, there is a possibility that two or more of the threads may access the same variable or another resource at the same time, and as a result, may cause a problem. For this reason, you should carefully consider how to make your code thread-safe.

The simplest mechanism for implementing thread safety is to use an object variable as a flag or traffic light to indicate when a shared resource has an exclusive lock applied.

In William Golding’s Lord of the Flies, Piggy and Ralph spot a conch shell and use it to call a meeting. The boys impose a “rule of the conch” on themselves, deciding that no one can speak unless they’re holding the conch.

I like to name the object variable I use for implementing thread-safe code the “conch.” When a thread has the conch, no other thread should access the shared resource(s) represented by that conch. Note...