The only guide you’ll need on concurrency & multithreading for senior engineers. Pressure test your skills with real-world practice problems from top companies.

Concurrency in Java is one of the most complex and advanced topics brought up during senior engineering interviews. Knowledge of concurrency and multithreading can put interviewees at a considerable advantage. This course lays the foundations of advanced concurrency and multithreading and explains concepts such as Monitors and Deferred Callbacks in depth. It also builds simple and complete solutions to popular concurrency problems that can be asked about in interviews like the Reader-Writer Problem and the Dining Philosopher Problem. While prior knowledge of concurrency is not required to follow through with this course, familiarity with the very basics of concurrency would be helpful.

Java Multithreading for Senior Engineering Interviews

## CompletionService Interface
In the previous lesson we discussed how tasks can be submitted to executors but imagine a scenario where you want to submit hundreds or thousands of tasks. You'll retrieve the future objects returned from the submit calls and then poll all of them in a loop to check which one is done and then take appropriate action. Java offers a better way to address this use case through the <code class="intf">CompletionService</code> interface. You can use the <code class="clazz">ExecutorCompletionService</code> as a concrete implementation of the interface.
The completion service is a combination of a blocking queue and an executor. Tasks are submitted to the queue and then the queue can be polled for completed tasks. The service exposes two methods, one <code class="mthd">poll</code> which returns null if no task is completed or none were submitted and two <code class="mthd">take</code> which blocks till a completed task is available.
Below is an example program that demonstrates the use of completion service.

# CompletionService Interface
In the previous lesson we discussed how tasks can be submitted to executors but imagine a scenario where you want to submit hundreds or thousands of tasks. You'll retrieve the future objects returned from the submit calls and then poll all of them in a loop to check which one is done and then take appropriate action. Java offers a better way to address this use case through the <code class="intf">CompletionService</code> interface. You can use the <code class="clazz">ExecutorCompletionService</code> as a concrete implementation of the interface.
The completion service is a combination of a blocking queue and an executor. Tasks are submitted to the queue and then the queue can be polled for completed tasks. The service exposes two methods, one <code class="mthd">poll</code> which returns null if no task is completed or none were submitted and two <code class="mthd">take</code> which blocks till a completed task is available.
Below is an example program that demonstrates the use of completion service.

# CompletionService Interface
In the previous lesson we discussed how tasks can be submitted to executors but imagine a scenario where you want to submit hundreds or thousands of tasks. You'll retrieve the future objects returned from the submit calls and then poll all of them in a loop to check which one is done and then take appropriate action. Java offers a better way to address this use case through the <code>CompletionService</code> interface. You can use the <code>ExecutorCompletionService</code> as a concrete implementation of the interface.
The completion service is a combination of a blocking queue and an executor. Tasks are submitted to the queue and then the queue can be polled for completed tasks. The service exposes two methods, one <code>poll</code> which returns null if no task is completed or none were submitted and two <code>take</code> which blocks till a completed task is available.
Below is an example program that demonstrates the use of completion service.

This lesson talks about how to batch multiple tasks together

The Basics

Multithreading in Java

Java's Memory Model

Interview Practice Problems

Bonus Questions

Beyond the Interview

Java Concurrency Reference

Revision & Quizzes

CompletionService Interface

CompletionService Interface