Java multi-threading on an Intel core i5 processor-CodePudding

I am working on a PC with an Intel Core i5 processor which reports to have 12 processors, which I believe is comprised of 6 cores each with two threads.

I have done some research and it appears that Java uses kernel threading. I need to dramatically increase the performance of an existing Java program and am hoping I can use all 12 of the core i5 threads to do this.

I am trying to use the IntStream().parallel.forEach() Java 1.8 feature which looks like I can parallelize nested for() loops with as many threads as available.

My concern is: whether my code can use all twelve threads or just the two threads on one core?

CodePudding user response：

For knowing how many processors you could use at your machine you could use availableProcessors(), snippet from java doc:

Returns the number of processors available to the Java virtual machine. This value may change during a particular invocation of the virtual machine. Applications that are sensitive to the number of available processors should therefore occasionally poll this property and adjust their resource usage appropriately

Code:

public class CoresDemo {
    public static void main(String[] args) {
        int nCores = Runtime.getRuntime().availableProcessors();
        System.out.println(nCores);
    }
}

CodePudding user response：

Java parallel stream uses ForkJoinPool.commonPool; which calculates total threads by Runtime.getRuntime().availableProcessors() - 1 (this is for leaving one processor calling thread).

So in your case it would be 12 -1 = 11 processors.

So you might be able to use 11 threads for your multithreading operations.

E.g. on my system I do have 8 available processors & I can see below operations is being performed by 7 threads:

System.out.println(Runtime.getRuntime().availableProcessors());
        IntStream.range(0, 1000000).parallel()
                .forEach(value -> System.out.println(value   "  "   Thread.currentThread().getName()));