Does Java have support for multicore processors/parallel processing?

Question

I know that now that most processors have two or more cores, multicore programming is all the rage. Is there functionality to utilize this in Java? I know that Java has a Thread class, but I also know this was around a long time before multicores became popular. If I can make use of multiple cores in Java, what class/technique would I use?

Answer 1

Does Java have support for multicore processors/parallel processing?

Yes. It also has been a platform for other programming languages where the implementation added a "true multithreading" or "real threading" selling point. The G1 Garbage Collector introduced in newer releases also makes use of multi-core hardware.

Java Concurrency in Practice

Try to get a copy of the Java Concurrency in Practice book.

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If I can make use of multiple cores in Java, what class/technique would I use?

java.util.concurrent

Utility classes commonly useful in concurrent programming. This package includes a few small standardized extensible frameworks, as well as some classes that provide useful functionality and are otherwise tedious or difficult to implement. Here are brief descriptions of the main components.

Executors

Executor is a simple standardized interface for defining custom thread-like subsystems, including thread pools, asynchronous IO, and lightweight task frameworks.

Queues

The java.util.concurrent ConcurrentLinkedQueue class supplies an efficient scalable thread-safe non-blocking FIFO queue.

Timing

The TimeUnit class provides multiple granularities (including nanoseconds) for specifying and controlling time-out based operations. Most classes in the package contain operations based on time-outs in addition to indefinite waits.

Synchronizers

Four classes aid common special-purpose synchronization idioms. Semaphore is a classic concurrency tool. CountDownLatch is a very simple yet very common utility for blocking until a given number of signals, events, or conditions hold. [...]

Concurrent Collections

Besides Queues, this package supplies a few Collection implementations designed for use in multithreaded contexts: ConcurrentHashMap, CopyOnWriteArrayList, and CopyOnWriteArraySet.

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This also comes in handy if you want to match the number of threads to the number of available CPUs for example:

int n = Runtime.getRuntime().availableProcessors();

Answer 2

In most Java implementations, you can rely on Java threads being real OS threads. As a result, the operating system will take care of making sure that the workload is distributed across multiple cores if you use the Thread class.

Operating system threads pre-date commodity multicore systems by a long time, so that's not a concern really. The only difference multicore systems made was to allow time-multiplexed operating system threads to be executed as truly concurrent threads on multiple cores.

Answer 3

Java 5 introduced the java.util.concurrent package which helps in building concurrent applications that can benefit from multicore systems. This package goes way beyond the multithreading functionality offered in Java 1.4 and earlier (like synchronized, wait, notify, etc).

There's a proposal for Java 7 to include the Fork/Join framework to make use of multicore systems easier.

Answer 4

You'll find new functionality in Ateji PX, an extension of the Java language with parallel primitives inspired from pi-calculus. Quite different from thread programming and everything thread-based (Tasks, Executors, etc).

Parallelism introduced this way at the language level, as opposed to threading librairies that provide API access to a mostly hardware-level concept, makes multicore programming much simpler and intuitive.

It's a radically new approach to parallel programming worth reading about (disclaimer: I am the designer of Ateji PX). The whitepaper is here : http://www.ateji.com/px/whitepapers/Ateji%20PX%20for%20Java%20v1.0.pdf.