How does ReferenceQueue behave in multithreaded code?

In Java, a ReferenceQueue is used with reference types such as SoftReference, WeakReference, and PhantomReference. It allows you to track when a reference has been cleared by the garbage collector. In multithreaded code, ReferenceQueue can have specific behaviors that need to be managed carefully.

When a reference object is no longer reachable, the garbage collector will enqueue it to the associated ReferenceQueue. In a multithreaded environment, it's possible for multiple threads to be waiting for references to be enqueued. Thus, synchronization is key to avoid missed notifications and to ensure that all threads are aware of the current state of the ReferenceQueue.