Parallel for loop with specific number of threads

Question

What is the best way, how to implement parallel for loop with a specified number of threads? Like this:

int maxThreads=5;
int curretnThreads=0;

for(int i = 0; i < 10000; i++){

   if(currentThreads<maxThreads){

      start thread...... 

   }else{
        wait...
   }

}

I would say the best way is to use the Java 8 Stream API. The second best way is to use ExecutorService.fixedThreadPool. The absolute worst way is to use raw Threads. — Boris the Spider
– Boris the Spider, Commented Jan 1, 2015 at 17:56

Boris the Spider · Accepted Answer · 2015-01-01 18:01:17Z

2

I would first create a ForkJoinPool with a fixed number of threads:

final ForkJoinPool forkJoinPool = new ForkJoinPool(numThreads);

Now simply execute a parallel stream operation in a task:

forkJoinPool.submit(() -> {
    IntStream.range(0, 10_000)
            .parallel()
            .forEach(i -> {
                //do stuff
            });
});

Obviously this example simply translates your code literally. I would recommend that you use the Stream API to its fullest rather than just loop [0, 10,000).

answered Jan 1, 2015 at 18:01

Boris the Spider

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