在Fork/Join框架中，提交任務的時候，有同步和非同步兩種方式。以前使用的invokeAll()的方法是同步的，也就是任

務提交後，這個方法不會返回直到所有的任務都處理完了。而還有另一種方式，就是使用fork方法，這個是非同步的。也

就是你提交任務後，fork方法立即返回，可以繼續下面的任務。這個執行緒也會繼續執行。

下面我們以一個查詢磁碟的以log結尾的檔案的程式例子來說明非同步的用法。

package com.bird.concursey.charpet8;import java.io.File;import java.util.ArrayList;import java.util.List;import java.util.concurrent.ForkJoinPool;import java.util.concurrent.RecursiveTask;public class FolderProcessor extends RecursiveTask<List<String>> { private static final
 
 long serialVersionUID = 1L;  private String path; private String extension; public FolderProcessor(String path, String extension) {  super();  this.path = path;  this.extension = extension; } @Override protected List<String> compute
 
() {  List<String> list = new ArrayList<String>();  List<FolderProcessor> tasks = new ArrayList<FolderProcessor>();  File file = new File(path);  File content[] = file.listFiles();  if(content != null) {   for(int i = 0; i < content.length; i++) {    if(content[i].isDirectory()) {     FolderProcessor task = new FolderProcessor(content[i].getAbsolutePath(), extension);     //非同步方式提交任務     task.fork();     tasks.add(task);    }else{     if(checkFile(content[i].getName())) {      list.add(content[i].getAbsolutePath());     }    }   }  }  if(tasks.size() > 50) {   System.out.printf("%s: %d tasks ran.\n",file.getAbsolutePath(),tasks.size());  }    addResultsFromTasks(list,tasks);  return list; } /**  * that will add to the list of filesthe results returned by the subtasks launched by this task.  * @param list  * @param tasks  */ private void addResultsFromTasks(List<String> list,   List<FolderProcessor> tasks) {  for(FolderProcessor item: tasks) {   list.addAll(item.join());  } }  /**  * This method compares if the name of a filepassed as a parameter ends with the extension you are looking for  * @param name  * @return  */ private boolean checkFile(String name) {  return name.endsWith(extension); }  public static void main(String[] args) {  ForkJoinPool pool = new ForkJoinPool();  FolderProcessor system = new FolderProcessor("C:\\Windows", "log");  FolderProcessor apps = new FolderProcessor("C:\\Program Files", "log");    pool.execute(system);  pool.execute(apps);    pool.shutdown();    List<String> results = null;  results = system.join();  System.out.printf("System: %d files found.\n",results.size());    results = apps.join();  System.out.printf("Apps: %d files found.\n",results.size());     }}

ff Files

ff Other folders

If the task finds a folder, it creates another Task object to process that folder and sends it to
the pool using the fork() method. This method sends the task to the pool that will execute it
if it has a free worker-thread or it can create a new one. The method returns immediately, so
the task can continue processing the content of the folder. For every file, a task compares its
extension with the one it's looking for and, if they are equal, adds the name of the file to the
list of results.

Once the task has processed all the content of the assigned folder, it waits for the finalization
of all the tasks it sent to the pool using the join() method. This method called in a task
waits for the finalization of its execution and returns the value returned by the compute()
method. The task groups the results of all the tasks it sent with its own results and returns
that list as a return value of the compute() method.

The ForkJoinPool class also allows the execution of tasks in an asynchronous way. You
have used the execute() method to send the three initial tasks to the pool. In the Main
class, you also finished the pool using the shutdown() method and wrote information about
the status and the evolution of the tasks that are running in it. The ForkJoinPool class
includes more methods that can be useful for this purpose. See the Monitoring a Fork/Join
pool recipe to see a complete list of those methods.

再分享一下我老師大神的人工智慧教程吧。零基礎！通俗易懂！風趣幽默！還帶黃段子！希望你也加入到我們人工智慧的隊伍中來！https://blog.csdn.net/jiangjunshow