Reputation: 97

Java Multithreading - Assign threads to processor cores

I am writing an application in java which involves parallel computing. My question is how can I explicitly assign threads to cores? What is the programming logic for it?

Can anyone tell why class Executor is used? Thanks

Upvotes: 5

Answers (7)

zengr

Reputation: 38899

You cannot assign threads to cores.

Java7's fork/join framework addresses exactly the same problem. Automatically though (It will be designed for multi-core processors).
What you can do is to set Thread priority to prioritize your threads, if that's what you want to achieve.
JNI might be another direction to export, but an overkill I guess. You can look at Peter Lawrey's Java-Thread-Affinity which uses JNI (I haven't used it).

Upvotes: 9

rgrebski

Reputation: 2584

See Java Thread Affinity project.

Lock to CPU

try (AffinityLock al = AffinityLock.acquireLock()) {
    // do some work while locked to a CPU.
}

Lock core:

try (AffinityLock al = AffinityLock.acquireCore()) {
    // do some work while locked to a CPU.
}

Upvotes: 3

Patrick

Reputation: 31

As said, the JVM won't let you. But first, you should ask yourself why you're thinking about assigning threads to cores. This is probably not what you want to do.

The Executor class is used to schedule medium-sized "grains" of computation without incurring the overhead of creating too many threads. You may also want to try using parallel branches for a much more fine-grained scheduling, here are some code samples: http://www.ateji.com/px/codesamples.html

Upvotes: 1

Bozho

Reputation: 597046

You can't. See this article. The JVM will delegate this to the OS, which will handle it for you.

Upvotes: 2

gd1

Reputation: 11403

I don't think it's easy for you to explicitly assign threads to cores. Maybe you can use native instructions, but I doubt it can be done.

And unless you're doing some special benchmark, you really don't need to. Java threads are backed by native threads, and if the O.S. is modern enough, its kernel will dynamically assign (and re-assign) threads to cores in a way that is certainly better than yours, because it (hopefully) does load balancing.

Start some threads that perform long computations and then see processor usage from a task manager. You'll see many cores being used.

Upvotes: 2