Java中Fork/Join示例

我就是我 2023-08-17 16:56 95阅读 0赞

import java.util.concurrent.ForkJoinPool;
    import java.util.concurrent.ForkJoinTask;
    import java.util.concurrent.RecursiveTask;
    
    public class SumTask extends RecursiveTask<Long> {
    
        static final int THRESHOLD = 100;
        long[] array;
        int start;
        int end;
    
        SumTask(long[] array, int start, int end) {
            this.array = array;
            this.start = start;
            this.end = end;
        }
    
        @Override
        protected Long compute() {
            if (end - start <= THRESHOLD) {
                long sum = 0;
                for (int i = start; i < end; i++) {
                    sum += array[i];
                }
                System.out.println(String.format("compute %d~%d = %d", start, end, sum));
                return sum;
            }
    
            int middle = (start + end) / 2;
            System.out.println(String.format("split%d~%d ==> %d~%d, %d~%d", start, end, start, middle, middle, end));
            SumTask subTask1 = new SumTask(this.array, start, middle);
            SumTask subTask2 = new SumTask(this.array, middle, end);
    
            invokeAll(subTask1, subTask2);
            Long subResult1 = subTask1.join();
            Long subResult2 = subTask2.join();
    
            long result = subResult1 + subResult2;
            System.out.println("result = " + subResult1 + " + " + subResult2 + " ==> " + result);
            return result;
        }
    
        public static void main(String[] args) {
            long[] array = new long[800];
            for (int i = 0; i < array.length; i++) {
                array[i] = i + 1;
            }
    
            // fork/join task
            ForkJoinPool fjp = new ForkJoinPool(4);
            ForkJoinTask<Long> task = new SumTask(array, 0, array.length);
            long startTime = System.currentTimeMillis();
            long result = fjp.invoke(task);
            long endTime = System.currentTimeMillis();
            System.out.println("Fork/Join sum: " + result + " in: " + (endTime - startTime) + " ms");
        }
    }

程序执行结果

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