在java中使用多线程并行化for循环

Question

I have a for loop in java with the following structure that I need to parallelize into a fixed number of threads. Lets say that number is in numThreads . The for loop is given below. Note that only the outer loop needs to be parallelized. I think I need to use Executor but I can't figure out how to split the workload into different threads, and if that will change my indexes inside the loop in statements like isInsulator[x][y] . basically I want different threads splitting the value of X and running a for loop for those x values assigned to them. Does that make sense? Can anyone help me achieve this or maybe push me in the right direction please?

Answer 1

1. Write a benchmark (so you can prove it's really faster with parallel processing), use JMH.
2. Rewrite the code to be a produce_inputs->process->collect_or_summarize pipeline
3. Use parallel Stream s API (it uses an internal fork-join pool tuned to the number of CPUs on the box).
4. Compare the performance of sequential vs paralle processing.

int result = IntStream.generate(() -> 42) // lazy inputs source
        .limit(100) // limit number of inputs
        .parallel() // use parallel processing
//      .sequential() // ...or sequential processing
        .map(x -> x + 1) // do the processing
        .reduce(0, Math::addExact); // summarize the result
//      .collect(toList()); // ...or just collect it to a container

Answer 2

You can declare a fixed thread pool (it will initialize and use only the specified number of threads):

Executor executor = Executors.newFixedThreadPool(numThreads);

You have to submit X tasks to the thread pool:

for (int i = 0; i < X; i++) {
        final int x = i;
        executor.execute(() -> submitTask(x));
}

In the method submitTask you can define your logic:

private void submitTask(final int x) {
    for (int y = 0; y < Y; y++) {
        //do stuff
    }
}