并发归并排序是一种使用并行计算的归并排序算法，在处理大数据集时可以提高排序效率。下面给出一个使用Java编写的并发归并排序的示例代码：

import java.util.Arrays;
import java.util.concurrent.*;

public class ConcurrentMergeSort {
    public static void main(String[] args) {
        int[] arr = {4, 2, 9, 1, 5, 7, 6, 3, 8};
        int[] sortedArr = concurrentMergeSort(arr);
        System.out.println(Arrays.toString(sortedArr));
    }

    public static int[] concurrentMergeSort(int[] arr) {
        if (arr.length <= 1) {
            return arr;
        }

        int mid = arr.length / 2;
        int[] left = Arrays.copyOfRange(arr, 0, mid);
        int[] right = Arrays.copyOfRange(arr, mid, arr.length);

        ExecutorService executorService = Executors.newFixedThreadPool(2);
        Future futureLeft = executorService.submit(() -> concurrentMergeSort(left));
        Future futureRight = executorService.submit(() -> concurrentMergeSort(right));

        try {
            int[] sortedLeft = futureLeft.get();
            int[] sortedRight = futureRight.get();
            return merge(sortedLeft, sortedRight);
        } catch (InterruptedException | ExecutionException e) {
            e.printStackTrace();
        } finally {
            executorService.shutdown();
        }

        return arr;
    }

    public static int[] merge(int[] left, int[] right) {
        int[] merged = new int[left.length + right.length];
        int i = 0, j = 0, k = 0;

        while (i < left.length && j < right.length) {
            if (left[i] <= right[j]) {
                merged[k++] = left[i++];
            } else {
                merged[k++] = right[j++];
            }
        }

        while (i < left.length) {
            merged[k++] = left[i++];
        }

        while (j < right.length) {
            merged[k++] = right[j++];
        }

        return merged;
    }
}

在上面的代码中，concurrentMergeSort方法是递归调用的，并且使用ExecutorService来实现并行计算。在每次递归调用中，将数组一分为二，分别对左右两部分进行并行排序。最后，使用merge方法将排序好的左右两部分合并起来。

需要注意的是，上述代码仅为示例，实际使用并发归并排序时需要根据具体情况进行调整和优化。