Explore multithreading and concurrency concepts in Java, from the basics on upward.

Java for Programmers

Java Multithreading

## 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 Memory Model

Java Thread Basics

CompletionService Interface

CompletionService Interface