Threads in Java - CountDownLatch (Part 12)

A CountDownLatch is a synchronizer which allows one thread to wait for one or more threads before starts processing.
A good application of CountDownLatch is in Java server-side applications where a thread cannot start execution before all the required services are started.

Working

A CountDownLatch is initialized with a given count which is the number of threads it should wait for. This count is decremented by calling countDown() method by the threads once they are finished execution. As soon as the count reaches to zero, the waiting task starts running.

Code Example

Let us say we require three services, LoginService, DatabaseService and CloudService to be started and ready before the application can start handling requests.

Output

Cloud Service is up!
Login Service is up!
Database Service is up!
All services are up. Now the waiting thread can start execution.

Here, we can see that the main thread is waiting for all the three services to start before starting its own execution. Once all the services (threads) are started, it can perform its own execution.

Conclusion

Congratulations!! 🙋 today we discussed CountDownLatch with an example. I hope you enjoyed this post.

You can find the complete code of this project on my GitHub in this commit. Feel free to fork or open issues, if any.

I would love to hear your thoughts on this and would like have suggestions from you to make it better.

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Happy Coding 😊

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