В чем разница между newFixedThreadPool и…

newFixedThreadPool creates a thread pool of fixed size, where each thread executes tasks sequentially. This is a classic thread pool from Executors, suitable for parallel execution of independent tasks with a limit on the number of concurrently running threads.

ForkJoinPool is a specialized thread pool optimized for tasks that can be recursively broken down into subtasks (fork) and then combined (join). It uses a work-stealing algorithm, where idle threads 'steal' tasks from busy threads, increasing efficiency when executing a large number of small tasks.

Example of using ForkJoinPool for parallel array summation:

import java.util.concurrent.*;

class SumTask extends RecursiveTask<Integer> {
    private final int[] arr;
    private final int start, end;
    private static final int THRESHOLD = 10;

    SumTask(int[] arr, int start, int end) {
        this.arr = arr;
        this.start = start;
        this.end = end;
    }

    @Override
    protected Integer compute() {
        if (end - start <= THRESHOLD) {
            int sum = 0;
            for (int i = start; i < end; i++) {
                sum += arr[i];
            }
            return sum;
        } else {
            int mid = (start + end) / 2;
            SumTask left = new SumTask(arr, start, mid);
            SumTask right = new SumTask(arr, mid, end);
            left.fork();
            int rightResult = right.compute();
            int leftResult = left.join();
            return leftResult + rightResult;
        }
    }
}

// Usage:
ForkJoinPool pool = new ForkJoinPool();
int[] data = {1,2,3,4,5,6,7,8,9,10};
int result = pool.invoke(new SumTask(data, 0, data.length));
System.out.println("Sum: " + result);

Thus, newFixedThreadPool is suitable for simple parallelism with a fixed number of threads, while ForkJoinPool is used for tasks with recursive splitting and high degrees of parallelism.

В чем разница между newFixedThreadPool и ForkJoinPool?