What is the purpose of synchronousqueue in Java?

In Java, SynchronousQueue is a special type of blocking queue used to pass single elements between multiple threads. This queue does not have a capacity and can only hold one element at a time. When a thread tries to put an element into the queue, it will be blocked until another thread takes that element out. Similarly, when a thread tries to take an element from the queue, it will also be blocked until another thread puts an element into the queue.

SynchronousQueue emphasizes direct interaction between threads, providing a mechanism for synchronous communication. It is commonly used for task scheduling in thread pools, where the main thread puts tasks into the SynchronousQueue, and worker threads then retrieve and process the tasks, ensuring synchronization between task submission and execution.

It’s important to note that SynchronousQueue does not store elements, it is only used for transferring elements. Therefore, if there is no thread waiting to retrieve an element, any attempt to insert an element will be blocked until another thread takes it. Similarly, if there is no thread trying to insert an element, any attempt to retrieve an element will also be blocked until another thread inserts an element. This feature makes SynchronousQueue very useful for data transfer between threads.