How to Synchronize Threads in Java Using CountDownLatch for Efficient Database Initialization?

Awaiting a Threads Output in Java

Within a Java application composed of two persistent threads, one for application logic and the other for database access, it's sometimes necessary for the application thread to await the database thread's output before proceeding. This article explores a solution using CountDownLatch for this scenario.

Both threads run concurrently throughout the application's lifetime, with one handling server communication and the other handling user interactions. However, on application initialization, it's crucial to ensure that the application thread pauses until the database thread becomes ready.

Polling methods like while (!dbthread.isReady()) {} are resource-intensive due to their continuous processor cycles consumption. Therefore, a more efficient approach is to use a CountDownLatch, which allows the application thread to wait for specific conditions before proceeding.

Initializing a CountDownLatch with a counter of 1 (e.g., CountDownLatch latch = new CountDownLatch(1);) creates a latch that will await for a single count before releasing. To do so, the application thread calls latch.await();, which effectively pauses its execution until either a countDown() is called or an optional timeout period expires.

Within the database thread, when it's ready to proceed, a single call to latch.countDown(); signals that the condition has been met and releases the waiting application thread. This synchronization ensures that both threads operate concurrently while maintaining the necessary sequence of operations.

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