Coordination Utilities
Explore key Java coordination utilities such as CountDownLatch, Semaphore, and CyclicBarrier to manage thread timing and access synchronization. Understand their differences and usage scenarios to write clear, efficient, and deadlock-free concurrent code in complex systems.
We’ve explored how to execute tasks asynchronously using the ExecutorService and combine their results with CompletableFuture. However, executing tasks is only half the battle. In complex systems, threads often need to coordinate their timing. You might need to pause a server startup until the database connection is ready, limit the number of users accessing a file simultaneously, or ensure a group of threads finishes a calculation phase before moving to the next one.
Writing this logic manually using low-level wait() and notify() is difficult, verbose, and error-prone. Java solves this with a set of high-level synchronization utilities found in the java.util.concurrent package. These tools act as traffic controllers, allowing us to enforce precise timing and access rules with minimal code.
Waiting for events with CountDownLatch
A CountDownLatch allows one or more threads to wait until a set of operations being performed in other threads completes. Think of it as a gate secured by a specific number of locks. As each task finishes, it unlocks one lock. Once all locks are released, the gate opens and the waiting threads proceed.
The latch is initialized with the number of completion signals we need (a positive integer).
Worker threads call
countDown()...