How to Synchronize Threads in Java Without Blocking: Using CountDownLatch for Thread-to-Thread Communication

How to Synchronize Threads in Java: A Practical Solution for Thread-to-Thread Communication

In Java programming, coordinating multiple threads for seamless execution is crucial. Consider a scenario where you have an application-logic thread and a database-access thread that must run concurrently. These threads require certain dependencies to be fulfilled before proceeding. This article explores a technique to synchronize the application thread, ensuring it waits for the database thread to become ready.

The Challenge: Synchronization without Blocking

Typically, Thread.join() is used to block a thread until another thread finishes its execution. However, in this case, both threads must continue running throughout the application's lifetime. Blocking one thread would not suffice.

The Solution: CountDownLatch

The solution lies in utilizing a CountDownLatch. This class employs a counter that acts as a rendezvous point for threads.

Implementation in Application Thread:

In the application thread, create a CountDownLatch with a count of 1:

CountDownLatch latch = new CountDownLatch(1);

Next, instruct the application thread to wait for the database thread to become ready:

latch.await();

This call will block the application thread until the database thread signals that it's ready.

Implementation in Database Thread:

In the database thread, once the initialization process is complete, it should decrement the CountDownLatch counter:

latch.countDown();

This action will release the application thread from its waiting state, allowing both threads to continue their operations seamlessly.

Advantages:

Using CountDownLatch offers several advantages:

• It ensures synchronization without blocking the execution of either thread.
• It provides a reliable way to signal readiness between threads, facilitating smooth thread coordination.
• It allows for flexible waiting periods, enabling fine-grained control over thread synchronization.

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