arthur.dy.lee

Fork/Join框架介绍IV-异常处理及取消任务【在数组中找指定数值，一旦找到立马停止任务的运行】

Fork/Join-异常处理及取消任务

在ForkJoinPool类中执行ForkJoinTask对象时，在任务开始执行前可以取消它。ForkJoinTask类提供了cancel()方法来达到取消任务的目的。在取消一个任务时必须要注意以下两点：

1、 ForkJoinPool类不提供任何方法来取消线程池中正在运行或者等待运行的所有任务；
2、取消任务时，不能取消已经被执行的任务。

实例

在本节，我们将实现一个取消ForkJoinTask对象的范例。该范例将寻找数组中某个数字所处的位置。第一个任务是寻找可以被取消的剩余任务数。由于Fork／Join框架没有提供取消功能，我们将创建一个辅助类来实现取消任务的操作。

注意：下面的代码，是在有1000个整数的数组中，查找数值等于5的数组位置，一经找到，就立马停止任务，但已经在运行的任务则无测取消。所以，数组中可能有95个位置有5，但是找出来的只有30多个，例子只是说明，一经找到就会停止任务。其实我觉得这种情况只适合在众多的数据中找一个的情况。

代码如下：
Main.java

package com.packtpub.java7.concurrency.chapter5.recipe05.core;

import java.util.concurrent.ForkJoinPool;
import java.util.concurrent.TimeUnit;

import com.packtpub.java7.concurrency.chapter5.recipe05.task.SearchNumberTask;
import com.packtpub.java7.concurrency.chapter5.recipe05.util.ArrayGenerator;
import com.packtpub.java7.concurrency.chapter5.recipe05.util.TaskManager;

/**
 * Main class of the program. 
 */
public class Main {

    /**
     * Main method of the example
     * @param args
     */
    public static void main(String[] args) {

        // Generate an array of 1000 integers
        ArrayGenerator generator=new ArrayGenerator();
        int array[]=generator.generateArray(1000);

        // Create a TaskManager object
        TaskManager manager=new TaskManager();

        // Create a ForkJoinPool with the default constructor
        ForkJoinPool pool=new ForkJoinPool();

        // Create a Task to process the array
        SearchNumberTask task=new SearchNumberTask(array,0,1000,5,manager);

        // Execute the task
        pool.execute(task);

        // Shutdown the pool
        pool.shutdown();


        // Wait for the finalization of the task
        try {
            pool.awaitTermination(1, TimeUnit.DAYS);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }

        // Write a message to indicate the end of the program
        System.out.printf("Main: The program has finished\n");
    }

}

ArrayGenerator.java

package com.packtpub.java7.concurrency.chapter5.recipe05.util;

import java.util.Random;

/**
 * Class that generates an array of integer numbers between 0 and 10
 * with a size specified as parameter
 *
 */
public class ArrayGenerator {

    /**
     * Method that generates an array of integer numbers between 0 and 10
     * with the specified size
     * @param size The size of the array
     * @return An array of random integer numbers between 0 and 10
     */
    public int[] generateArray(int size) {
        int count = 0;
        int array[]=new int[size];
        Random random=new Random();
        for (int i=0; i10);
            if(array[i]==5){
                System.out.print(i+", ");
                count++;
            }
        }
        System.out.println("------------------");
        System.out.println("count: "+count);
        return array;
    }

}

TaskManager.java

package com.packtpub.java7.concurrency.chapter5.recipe05.util;

import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.ForkJoinTask;

import com.packtpub.java7.concurrency.chapter5.recipe05.task.SearchNumberTask;

/**
 * Class that stores all the tasks that have been sent to
 * a ForkJoinPool. Provides a method for the cancellation of
 * all the tasks
 *
 */
public class TaskManager {

    /**
     * List of tasks
     */
    private List> tasks;

    /**
     * Constructor of the class. Initializes the list of tasks
     */
    public TaskManager(){
        tasks=new ArrayList<>();
    }

    /**
     * Method to add a new Task in the list
     * @param task The new task
     */
    public void addTask(ForkJoinTask task){
        tasks.add(task);
    }

    /**
     * Method that cancel all the tasks in the list
     * @param cancelTask 
     */
    public void cancelTasks(ForkJoinTask cancelTask){
        for (ForkJoinTask task  :tasks) {
            if (task!=cancelTask) {
                task.cancel(true);
                ((SearchNumberTask)task).writeCancelMessage();
            }
        }
    }
}

SearchNumberTask.java

package com.packtpub.java7.concurrency.chapter5.recipe05.task;

import java.util.concurrent.RecursiveTask;
import java.util.concurrent.TimeUnit;

import com.packtpub.java7.concurrency.chapter5.recipe05.util.TaskManager;

/**
 * This task look for a number in an array of integer numbers.
 * If the part of the array it has to process has more than
 * 10 elements, it creates two subtasks and executes then asynchronously
 * with the fork method. Otherwise, look for the number in the block
 * it has to process.
 * 
 * If the task found the number, return the position where the number has
 * been found. Else, return the -1 value. If a subtask found the number,
 * the tasks suspend the other subtask and return the position where the number
 * has been found. If none of the two subtasks found the number, return the -1
 * value.
 *
 */
public class SearchNumberTask extends RecursiveTask<Integer> {

    /**
     * Serial Version UID
     */
    private static final long serialVersionUID = 1L;

    /**
     * Valued returned when the number has not been found by the task
     */
    private final static int NOT_FOUND=-1;

    /**
     * Array of numbers
     */
    private int numbers[];

    /**
     * Start and end positions of the block of numbers
     * this task has to process
     */
    private int start, end;

    /**
     * Number this task is going to look for
     */
    private int number;

    /**
     * Object that allows the cancellation of all the tasks
     */
    private TaskManager manager;

    /**
     * Constructor of the class
     * @param array Array of numbers
     * @param start Start position of the block of numbers this task has to process 
     * @param end End position of the block of numbers this task has to process
     * @param number Number this task is going to look for
     * @param manager 
     */
    public SearchNumberTask(int numbers[], int start, int end, int number, TaskManager manager){
        this.numbers=numbers;
        this.start=start;
        this.end=end;
        this.number=number;
        this.manager=manager;
    }

    /**
     * If the block of number this task has to process has more than
     * ten elements, divide that block in two parts and create two
     * new Tasks using the launchTasks() method.
     * Else, looks for the number in the block assigned to it using
     * the lookForNumber() method
     */
    @Override
    protected Integer compute() {
        System.out.println("Task: "+start+":"+end);
        int ret;
        if (end-start>10) {
            ret=launchTasks();
        } else {
            ret=lookForNumber();
        }
        return new Integer(ret);
    }

    /**
     * Looks for the number in the block of numbers assigned to this task
     * @return The position where it found the number or -1 if it doesn't find it
     */
    private int lookForNumber() {
        for (int i=start; iif (numbers[i]==number) {
                System.out.printf("Task: Number %d found in position %d\n",number,i);
                manager.cancelTasks(this);
                return i;
            }
            try {
                TimeUnit.SECONDS.sleep(1);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
        return NOT_FOUND;
    }

    /**
     * Divide the block of numbers assigned to this task in two and 
     * execute to new Task objects to process that blocks 
     * @return The position where the number has been found of -1
     * if the number haven't been found in the subtasks
     */
    private int launchTasks() {
        int mid=(start+end)/2;

        SearchNumberTask task1=new SearchNumberTask(numbers,start,mid,number,manager);
        SearchNumberTask task2=new SearchNumberTask(numbers,mid,end,number,manager);

        manager.addTask(task1);
        manager.addTask(task2);

        task1.fork();
        task2.fork();
        int returnValue;

        returnValue=task1.join();
        if (returnValue!=-1) {
            return returnValue;
        }

        returnValue=task2.join();
        return returnValue;
    }

    public void writeCancelMessage(){
        System.out.printf("Task: Cancelled task from %d to %d\n",start,end);
    }

}

结果

0, 4, 14, 45, 67, 73, 77, 79, 102, 107, 115, 118, 119, 134, 165, 180, 183, 188, 192, 219, 228, 242, 253, 258, 270, 271, 273, 282, 304, 327, 328, 333, 348, 362, 394, 405, 411, 420, 424, 431, 452, 461, 477, 486, 494, 498, 505, 510, 537, 547, 550, 564, 568, 569, 573, 591, 620, 631, 634, 646, 654, 659, 723, 725, 735, 736, 739, 746, 753, 762, 768, 779, 783, 802, 810, 835, 836, 838, 844, 849, 854, 857, 867, 878, 888, 892, 912, 923, 948, 973, 974, 992, 998, ——————
count: 93
Task: 0:1000
Task: 500:1000
Task: 0:500
Task: 500:750
Task: 0:250
Task: 0:125
Task: 125:250
Task: 0:62
Task: 62:125
Task: 0:31
Task: 500:625
Task: 31:62
Task: 625:750
Task: 31:46
Task: 31:38
Task: 46:62
Task: 62:93
Task: 38:46
Task: 500:562
Task: Number 5 found in position 45
Task: Cancelled task from 0 to 500
Task: Cancelled task from 500 to 1000
Task: 93:125
Task: 750:1000
Task: Cancelled task from 500 to 750
Task: 0:15
Task: 93:109
Task: 125:187
Task: 625:687
Task: 46:54
Task: 15:31
Task: 54:62
Task: 15:23
Task: 625:656
Task: 23:31
Task: 109:125
Task: 500:531
Task: 500:515
Task: 187:250
Task: 0:7
Task: Number 5 found in position 0
Task: Cancelled task from 0 to 500
Task: Cancelled task from 500 to 1000
Task: Cancelled task from 500 to 750
Task: Cancelled task from 750 to 1000
Task: Cancelled task from 0 to 250
Task: 250:500
Task: Cancelled task from 250 to 500
Task: 515:531
Task: 7:15
Task: 93:101
Task: 62:77
Task: 187:218
Task: 125:156
Task: Number 5 found in position 14
Task: Cancelled task from 0 to 500
Task: Cancelled task from 500 to 1000
Task: Cancelled task from 500 to 750
Task: Cancelled task from 750 to 1000
Task: Cancelled task from 0 to 250
Task: Cancelled task from 250 to 500
Task: Cancelled task from 500 to 625
Task: 500:507
Task: Cancelled task from 625 to 750
Task: Cancelled task from 0 to 125
Task: Cancelled task from 125 to 250
Task: Cancelled task from 0 to 62
Task: Cancelled task from 62 to 125
Task: Cancelled task from 125 to 187
Task: Cancelled task from 187 to 250
Task: Cancelled task from 0 to 31
Task: Cancelled task from 31 to 62
Task: Cancelled task from 62 to 93
Task: Cancelled task from 93 to 125
Task: Cancelled task from 0 to 15
Task: Cancelled task from 15 to 31
Task: Cancelled task from 500 to 562
Task: 625:640
Task: Cancelled task from 562 to 625
Task: 250:375
Task: 562:625
Task: 515:523
Task: 101:109
Task: 156:187
Task: Number 5 found in position 102
Task: Cancelled task from 0 to 500
Task: Cancelled task from 500 to 1000
Task: Cancelled task from 500 to 750
Task: Cancelled task from 750 to 1000
Task: Cancelled task from 0 to 250
Task: Cancelled task from 250 to 500
Task: Cancelled task from 500 to 625
Task: Cancelled task from 625 to 750
Task: Cancelled task from 0 to 125
Task: Cancelled task from 125 to 250
Task: Cancelled task from 0 to 62
Task: Cancelled task from 62 to 125
Task: Cancelled task from 125 to 187
Task: Cancelled task from 187 to 250
Task: Cancelled task from 0 to 31
Task: Cancelled task from 31 to 62
Task: Cancelled task from 62 to 93
Task: Cancelled task from 93 to 125
Task: Cancelled task from 0 to 15
Task: Cancelled task from 15 to 31
Task: Cancelled task from 500 to 562
Task: Cancelled task from 562 to 625
Task: Cancelled task from 31 to 46
Task: Cancelled task from 46 to 62
Task: 687:750
Task: Cancelled task from 625 to 687
Task: 109:117
Task: 531:562
Task: Number 5 found in position 505
Task: Cancelled task from 0 to 500
Task: Cancelled task from 500 to 1000
Task: Cancelled task from 500 to 750
Task: Cancelled task from 750 to 1000
Task: Cancelled task from 0 to 250
Task: Cancelled task from 250 to 500
Task: Cancelled task from 500 to 625
Task: Cancelled task from 625 to 750
Task: Cancelled task from 0 to 125
Task: Cancelled task from 125 to 250
Task: Cancelled task from 0 to 62
Task: Cancelled task from 62 to 125
Task: Cancelled task from 125 to 187
Task: Cancelled task from 187 to 250
Task: Cancelled task from 0 to 31
Task: Cancelled task from 31 to 62
Task: Cancelled task from 62 to 93
Task: Cancelled task from 93 to 125
Task: Cancelled task from 0 to 15
Task: Cancelled task from 15 to 31
Task: Cancelled task from 500 to 562
Task: Cancelled task from 562 to 625
Task: Cancelled task from 31 to 46
Task: Cancelled task from 46 to 62
Task: Cancelled task from 625 to 687
Task: Cancelled task from 687 to 750
Task: Cancelled task from 31 to 38
Task: Cancelled task from 38 to 46
Task: Cancelled task from 46 to 54
Task: Cancelled task from 54 to 62
Task: Cancelled task from 62 to 77
Task: 77:93
Task: Cancelled task from 77 to 93
Task: 625:632
Task: 507:515
Task: Number 5 found in position 115
Task: 523:531
Task: 750:875
Task: Cancelled task from 0 to 500
Task: 125:140
Task: 117:125
Task: Number 5 found in position 510
Task: Cancelled task from 0 to 500
Task: Cancelled task from 500 to 1000
Task: Cancelled task from 500 to 750
Task: Cancelled task from 750 to 1000
Task: Cancelled task from 0 to 250
Task: Cancelled task from 250 to 500
Task: Cancelled task from 500 to 625
Task: Cancelled task from 625 to 750
Task: Cancelled task from 0 to 125
Task: Cancelled task from 125 to 250
Task: Cancelled task from 0 to 62
Task: Cancelled task from 62 to 125
Task: Cancelled task from 125 to 187
Task: Cancelled task from 187 to 250
Task: Cancelled task from 0 to 31
Task: Cancelled task from 31 to 62
Task: Cancelled task from 62 to 93
Task: Cancelled task from 93 to 125
Task: Cancelled task from 0 to 15
Task: Cancelled task from 15 to 31
Task: Cancelled task from 500 to 562
Task: Cancelled task from 562 to 625
Task: Cancelled task from 31 to 46
Task: Cancelled task from 46 to 62
Task: Cancelled task from 625 to 687
Task: Cancelled task from 687 to 750
Task: Cancelled task from 31 to 38
Task: Cancelled task from 38 to 46
Task: Cancelled task from 46 to 54
Task: Cancelled task from 54 to 62
Task: Cancelled task from 62 to 77
Task: Cancelled task from 77 to 93
Task: Cancelled task from 500 to 531
Task: Cancelled task from 531 to 562
Task: Cancelled task from 93 to 109
Task: Cancelled task from 109 to 125
Task: Cancelled task from 750 to 875
Task: 875:1000
Task: Cancelled task from 875 to 1000
Task: 140:156
Task: 156:171
Task: 632:640
Task: Number 5 found in position 118
Task: Cancelled task from 0 to 500
Task: Cancelled task from 500 to 1000
Task: Cancelled task from 500 to 750
Task: Cancelled task from 750 to 1000
Task: Cancelled task from 0 to 250
Task: Cancelled task from 250 to 500
Task: Cancelled task from 500 to 625
Task: Cancelled task from 625 to 750
Task: Cancelled task from 0 to 125
Task: Cancelled task from 125 to 250
Task: Cancelled task from 0 to 62
Task: Cancelled task from 62 to 125
Task: Cancelled task from 125 to 187
Task: Cancelled task from 187 to 250
Task: Cancelled task from 0 to 31
Task: Cancelled task from 31 to 62
Task: Cancelled task from 62 to 93
Task: Cancelled task from 93 to 125
Task: Cancelled task from 0 to 15
Task: Cancelled task from 15 to 31
Task: Cancelled task from 500 to 562
Task: Cancelled task from 562 to 625
Task: Cancelled task from 31 to 46
Task: Cancelled task from 46 to 62
Task: Cancelled task from 625 to 687
Task: Cancelled task from 687 to 750
Task: Cancelled task from 31 to 38
Task: Cancelled task from 38 to 46
Task: Cancelled task from 46 to 54
Task: Cancelled task from 54 to 62
Task: Cancelled task from 62 to 77
Task: Cancelled task from 77 to 93
Task: Cancelled task from 500 to 531
Task: Cancelled task from 531 to 562
Task: Cancelled task from 93 to 109
Task: Cancelled task from 109 to 125
Task: Cancelled task from 750 to 875
Task: Cancelled task from 875 to 1000
Task: Cancelled task from 0 to 7
Task: Cancelled task from 7 to 15
Task: Cancelled task from 93 to 101
Task: Cancelled task from 101 to 109
Task: Cancelled task from 125 to 156
Task: Cancelled task from 156 to 187
Task: Cancelled task from 625 to 656
Task: Cancelled task from 656 to 687
Task: Cancelled task from 15 to 23
Task: Cancelled task from 23 to 31
Task: Cancelled task from 625 to 640
Task: Cancelled task from 640 to 656
Task: Cancelled task from 109 to 117
Task: Cancelled task from 500 to 515
Task: Cancelled task from 515 to 531
Task: Cancelled task from 500 to 507
Task: Cancelled task from 507 to 515
Task: Cancelled task from 187 to 218
Task: Cancelled task from 218 to 250
Task: 218:250
Task: 375:500
Task: Cancelled task from 250 to 375
Task: 62:69
Task: Number 5 found in position 634
Task: Cancelled task from 0 to 500
Task: Cancelled task from 500 to 1000
Task: Cancelled task from 500 to 750
Task: Cancelled task from 750 to 1000
Task: Cancelled task from 0 to 250
Task: Cancelled task from 250 to 500
Task: Cancelled task from 500 to 625
Task: Cancelled task from 625 to 750
Task: Cancelled task from 0 to 125
Task: Cancelled task from 125 to 250
Task: Cancelled task from 0 to 62
Task: Cancelled task from 62 to 125
Task: Cancelled task from 125 to 187
Task: Cancelled task from 187 to 250
Task: Cancelled task from 0 to 31
Task: Cancelled task from 31 to 62
Task: Cancelled task from 62 to 93
Task: Cancelled task from 93 to 125
Task: Cancelled task from 0 to 15
Task: Cancelled task from 15 to 31
Task: Cancelled task from 500 to 562
Task: Cancelled task from 562 to 625
Task: Cancelled task from 31 to 46
Task: Cancelled task from 46 to 62
Task: Cancelled task from 625 to 687
Task: Cancelled task from 687 to 750
Task: Cancelled task from 31 to 38
Task: Cancelled task from 38 to 46
Task: Cancelled task from 46 to 54
Task: Cancelled task from 54 to 62
Task: Cancelled task from 62 to 77
Task: Cancelled task from 77 to 93
Task: Cancelled task from 500 to 531
Task: Cancelled task from 531 to 562
Task: Cancelled task from 93 to 109
Task: Cancelled task from 109 to 125
Task: Cancelled task from 750 to 875
Task: Cancelled task from 875 to 1000
Task: Cancelled task from 0 to 7
Task: Cancelled task from 7 to 15
Task: Cancelled task from 93 to 101
Task: Cancelled task from 101 to 109
Task: Cancelled task from 125 to 156
Task: Cancelled task from 156 to 187
Task: Cancelled task from 625 to 656
Task: Cancelled task from 656 to 687
Task: Cancelled task from 15 to 23
Task: Cancelled task from 23 to 31
Task: Cancelled task from 625 to 640
Task: Cancelled task from 640 to 656
Task: Cancelled task from 109 to 117
Task: Cancelled task from 117 to 125
Task: Cancelled task from 500 to 515
Task: Cancelled task from 515 to 531
Task: Cancelled task from 500 to 507
Task: Cancelled task from 507 to 515
Task: Cancelled task from 187 to 218
Task: Cancelled task from 218 to 250
Task: Cancelled task from 250 to 375
Task: Cancelled task from 375 to 500
Task: Cancelled task from 515 to 523
Task: Cancelled task from 523 to 531
Task: Cancelled task from 62 to 69
Task: Cancelled task from 69 to 77
Task: Cancelled task from 187 to 202
Task: 202:218
Task: Cancelled task from 202 to 218
Task: 531:546
Task: 875:937
Task: 562:593
Task: 140:148
Task: Number 5 found in position 631
Task: Cancelled task from 0 to 500
Task: Cancelled task from 500 to 1000
Task: Cancelled task from 500 to 750
Task: Cancelled task from 750 to 1000
Task: Cancelled task from 0 to 250
Task: Cancelled task from 250 to 500
Task: Cancelled task from 500 to 625
Task: Cancelled task from 625 to 750
Task: Cancelled task from 0 to 125
Task: Cancelled task from 125 to 250
Task: Cancelled task from 0 to 62
Task: Cancelled task from 62 to 125
Task: Cancelled task from 125 to 187
Task: Cancelled task from 187 to 250
Task: Cancelled task from 0 to 31
Task: Cancelled task from 31 to 62
Task: Cancelled task from 62 to 93
Task: Cancelled task from 93 to 125
Task: Cancelled task from 0 to 15
Task: Cancelled task from 15 to 31
Task: Cancelled task from 500 to 562
Task: Cancelled task from 562 to 625
Task: Cancelled task from 31 to 46
Task: Cancelled task from 46 to 62
Task: Cancelled task from 625 to 687
Task: Cancelled task from 687 to 750
Task: Cancelled task from 31 to 38
Task: Cancelled task from 38 to 46
Task: Cancelled task from 46 to 54
Task: Cancelled task from 54 to 62
Task: Cancelled task from 62 to 77
Task: Cancelled task from 77 to 93
Task: Cancelled task from 500 to 531
Task: Cancelled task from 531 to 562
Task: Cancelled task from 93 to 109
Task: Cancelled task from 109 to 125
Task: Cancelled task from 750 to 875
Task: Cancelled task from 875 to 1000
Task: Cancelled task from 0 to 7
Task: Cancelled task from 7 to 15
Task: Cancelled task from 93 to 101
Task: Cancelled task from 101 to 109
Task: Cancelled task from 125 to 156
Task: Cancelled task from 156 to 187
Task: Cancelled task from 625 to 656
Task: Cancelled task from 656 to 687
Task: Cancelled task from 15 to 23
Task: Cancelled task from 23 to 31
Task: Cancelled task from 625 to 640
Task: Cancelled task from 640 to 656
Task: Cancelled task from 109 to 117
Task: Cancelled task from 117 to 125
Task: Cancelled task from 500 to 515
Task: Cancelled task from 515 to 531
Task: Cancelled task from 500 to 507
Task: Cancelled task from 507 to 515
Task: Cancelled task from 187 to 218
Task: Cancelled task from 218 to 250
Task: Cancelled task from 250 to 375
Task: Cancelled task from 375 to 500
Task: Cancelled task from 515 to 523
Task: Cancelled task from 523 to 531
Task: Cancelled task from 62 to 69
Task: Cancelled task from 69 to 77
Task: Cancelled task from 187 to 202
Task: Cancelled task from 202 to 218
Task: Cancelled task from 125 to 140
Task: Cancelled task from 140 to 156
Task: Cancelled task from 632 to 640
Task: Cancelled task from 250 to 312
Task: Cancelled task from 312 to 375
Task: Cancelled task from 562 to 593
Task: Cancelled task from 593 to 625
Task: Cancelled task from 156 to 171
Task: Cancelled task from 171 to 187
Task: Cancelled task from 687 to 718
Task: Cancelled task from 718 to 750
Task: Cancelled task from 531 to 546
Task: Cancelled task from 546 to 562
Task: Cancelled task from 77 to 85
Task: Cancelled task from 85 to 93
Task: Cancelled task from 750 to 812
Task: Cancelled task from 812 to 875
Task: Cancelled task from 125 to 132
Task: Cancelled task from 132 to 140
Task: Cancelled task from 875 to 937
Task: Cancelled task from 937 to 1000
Task: Cancelled task from 140 to 148
Task: Cancelled task from 148 to 156
Task: Cancelled task from 156 to 163
Task: Cancelled task from 163 to 171
Task: Cancelled task from 218 to 234
Task: Cancelled task from 234 to 250
Task: Cancelled task from 375 to 437
Task: Cancelled task from 437 to 500
Task: Cancelled task from 202 to 210
Task: Cancelled task from 210 to 218
Task: Cancelled task from 531 to 538
Task: Cancelled task from 538 to 546
Task: Cancelled task from 875 to 906
Task: Cancelled task from 906 to 937
Task: Cancelled task from 562 to 577
Task: Cancelled task from 577 to 593
Task: 312:375
Task: 577:593
Task: 906:937
Task: 538:546
Task: 210:218
Task: 437:500
Task: 234:250
Task: 163:171
Task: 148:156
Task: 937:1000
Task: 132:140
Task: 812:875
Task: 546:562
Task: 718:750
Task: 593:625
Task: Number 5 found in position 165
Task: Number 5 found in position 134
Task: Cancelled task from 0 to 500
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Main: The program has finished

工作原理

ForkJoinTask类提供的cancel()方法允许取消一个仍没有被执行的任务，这是非常重要的一点。如果任务已经开始执行，那么调用cancel()方法也无法取消。这个方法接收一个名为mayInterruptIfRunning的boolean值参数。顾名思义，如果传递true值给这个方法，即使任务正在运行也将被取消。JavaAPI文档指出，ForkJoinTask类的默认实现，这个属性没有起作用。如果任务还没有开始执行，那么这些任务将被取消。任务的取消对于已发送到线程池中的任务没有影响，它们将继续执行。

Fork／Join框架的局限性在于，ForkJoinPool线程池中的任务不允许被取消。为了克服这种局限性，我们实现了TaskManager类，它存储发送到线程池中的所有任务，可以用一个方法来取消存储的所有任务。如果任务正在运行或者已经执行结束，那么任务就不能被取消，cancel()方法返回false值，因此可以尝试去取消所有的任务而不用担心可能带来的间接影响。

这个范例实现在数字数组中寻找一个数字。根据Fork／Join框架的推荐，我们将问题拆分为更小的子问题。由于我们仅关心数字的一次出现，因此，当找到它时，就会取消其他的所有任务。

转自ifeve：http://ifeve.com/java7-concurrency-cookbook-4/

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一、概述记录时间[2024-08-16]前置知识：Java基础篇；Java面向对象多线程01：Java多线程学习导航，线程简介，线程相关概念的整理多线程02：线程实现，创建线程的三种方式，通过多线程下载图片案例分析异同（Thread，Runnable，Callable）Java多线程学习主要模块包括：线程简介；线程实现；线程控制；线程状态；线程同步；线程通信问题；拓展高级主题。本文是针对多线程的相
Java多线程的可重入和不可重入 @See you later Java java 开发语言
在Java中，可重入（Reentrant）和不可重入（Non-reentrant）这两个概念通常用于描述多线程环境下的同步方法或代码块的行为。可重入（Reentrant）可重入是指一个线程持有某个锁（Lock）时，可以再次请求同一个锁而不会被锁阻塞。换句话说，如果一个线程获取了某个对象的锁，它可以再次请求这个锁而不会导致死锁。Java中的synchronized关键字就是可重入的。当一个线程获取了
Java多线程：深入探索与详细解析 m0_63550220 java 开发语言
1.基础概念与重要性在Java编程中，多线程是并发编程的基石，它允许应用程序同时执行多个任务。这种能力不仅提高了程序的执行效率，还增强了其响应性和用户界面的流畅性。随着现代计算机系统的多核化趋势，多线程编程变得越来越重要，因为它能够充分利用硬件资源，提升程序的总体性能。线程（Thread）：作为Java中的基本执行单元，线程是轻量级的进程，由线程ID、程序计数器、Java虚拟机栈、本地方法栈、和线
JAVA多线程基础篇 8、线程隔离与ThreadLocal 悟空学编程 JAVA多线程基础篇 java 开发语言后端
文章目录1.ThreadLocal的使用示例2.ThreadLocal的使用场景2.1线程隔离的数据库连接与事务2.2线程隔离的session会话3.ThreadLocal原理4.ThreadLocal与内存泄露4.1Java语言将Entry设计为弱引用4.2记得手动remove总结在多线程并发环境中，要保证线程并发安全总体有2类方法。使用锁，在访问资源时是互斥的、原子性的。这个锁可以是Synch
java多线程:模拟ThreadLocal ╭╯Erica 并发编程 java 多线程
ThreadLocal存储的变量，同一线程下可见，不同线程不可见packagecom.tuyrk.chapter10;importjava.util.HashMap;importjava.util.Map;/***模拟ThreadLocal**/publicclassThreadLocalSimulator{privatefinalMapstorage=newHashMapthreadLocal=
Java多线程同步工具类：Semaphore原理剖析 JermeryBesian Java java jvm 面试多线程
Java多线程同步工具类：Semaphore原理剖析文章目录Java多线程同步工具类：Semaphore原理剖析Semaphore原理实战案例前驱知识准备：AbstractQueuedSynchronizer队列同步器[Java多线程之：队列同步器AbstractQueuedSynchronizer原理剖析]Semaphore原理Semaphore也就是信号量，提供了资源数量的并发访问控制，可以用
普通公司员工的编程水平与阿里巴巴有多大差距？ Java机械师
BAT的牛人多，普通人也多，虽然他们不是每个人都能达到令人仰望的技术水平，但毕竟平台高，所以眼光会变得宽阔；代码要求更为严格，所以普通的程序员也会被逼变得更优秀；身边的牛人多，普通的程序员也会受到影响，提升的更快。image正好今天看到一篇文章，是讲去阿里的面试经历，也分享给大家，看看自己离着【进】阿里还有多大的差距。Java多线程线程池的原理，为什么要创建线程池？线程的生命周期，什么时候会出现僵
java多线程缓存_java – 线程的多线程访问和变量缓存 weixin_39900736 java多线程缓存
问题是java只是一个规范.有许多JVM实现和物理操作环境的示例.在任何给定的组合上,动作可能是安全的或不安全的.例如,在单处理器系统上,示例中的volatile关键字可能完全没必要.由于存储器和语言规范的编写者无法合理地考虑可能的操作条件集,因此他们选择将某些模式列入白名单,这些模式可以保证适用于所有兼容的实现.遵守这些准则可确保您的代码可以在目标系统上运行,并且可以合理地移植.在这种情况下,“
“全栈2019”Java多线程第五十二章：LockSupport等待截止时间人人都是程序员
难度初级学习时间10分钟适合人群零基础开发语言Java开发环境JDKv11IntelliJIDEAv2018.3文章原文链接“全栈2019”Java多线程第五十二章：LockSupport等待截止时间下一章“全栈2019”Java多线程第五十三章：ThreadLocal简单介绍学习小组加入同步学习小组，共同交流与进步。方式一：加入编程圈子。方式二：关注头条号Gorhaf，私信“Java学习小组”。
JAVA多线程异步与线程池------JAVA 旧约Alatus JAVA #JUC多线程 java 缓存后端 mybatis 微服务 spring boot spring
初始化线程的四种方式继承Thread实现Runnable接口实现Callable接口+FutureTask(可以拿到返回结果,可以处理异常)线程池继承Thread和实现Runnable接口的方式,主进程无法获取线程的运算结果,不适合业务开发实现Callable接口+FutureTask可以获取线程内的返回结果,但是不利于控制服务器的线程资源,容易导致资源耗尽通过线程池的方式性能稳定,且可以获取结果
JAVA多线程等待唤醒机制我来变强了 JAVA java
为什么要处理线程间通信：当我们需要多个线程来共同完成一件任务，并且我们希望他们有规律的执行，那么多线程之间需要一些通信机制，可以协调它们的工作，以此实现多线程共同操作一份数据。比如：线程A用来生产包子的，线程B用来吃包子的，包子可以理解为同一资源，线程A与线程B处理的动作，一个是生产，一个是消费，此时B线程必须等到A线程完成后才能执行，那么线程A与线程B之间就需要线程通信，即——等待唤醒机制。这是
Java多线程中的锁机制：深入解析synchronized与ReentrantLock 杰哥在此 Java系列 java 开发语言
在Java多线程编程中，锁机制是确保线程安全的关键手段。当我们需要控制多个线程对共享资源的访问时，锁可以帮助我们实现这一目标。Java提供了两种主要的锁机制：synchronized关键字和ReentrantLock接口。本文将深入解析这两种锁机制的工作原理、使用场景以及性能特点。一、synchronized关键字synchronized是Java提供的一种内置锁机制，它可以用来修饰方法或代码块。
Java笔试面试题之多线程常见考点总结工程师老罗 Java笔试面试题AI答 java 开发语言
Java多线程面试题涵盖了Java多线程编程的多个重要方面，主要考察面试者对Java并发编程的理解和应用能力。以下是常见的考点总结：基本概念与区别：进程与线程的区别：进程是资源分配的基本单位，线程是CPU调度的基本单位，线程共享进程资源。Java堆与栈的区别：堆用于存储对象实例，栈用于存储局部变量和方法调用。线程创建与状态：线程创建方式：继承Thread类、实现Runnable接口、使用Calla
Java笔试面试题之多线程偏门考点总结工程师老罗 Java笔试面试题AI答 java 开发语言
以下一些偏门的Java多线程面试题考点：特定API的深入使用：Semaphore的具体应用场景和实现原理。文档中提到了Semaphore是什么，但没有深入探讨其在实际开发中的使用案例和细节。CyclicBarrier和CountDownLatch的具体实现原理和使用场景差异。尽管文档中提到了两者的区别，但可能缺乏具体的代码示例或更深入的分析。线程安全的高级概念：锁降级（LockDowngrade）
写一个Java多线程应用程序，模拟三个人排队买票，张三、李四和王五买电影票，售票员只有三张10元的钱，电影票10元钱一张。 xinkong1010 j2se 多线程 java thread string class
packagecom.online.test;/*编写一个Java多线程应用程序，模拟三个人排队买票，张三、李四和王五买电影票，售票员只有三张10元的钱，电影票10元钱一张。张三拿50元一张的人民币排在李四的前面买票，李四排在王五的前面拿一张20元的人民币买票，王五拿一张10元的人民币买票。*/publicclassMaipiao{publicstaticvoidmain(Stringargs[]
2024年Java多线程实战-从零手搓一个简易线程池(一)定义任务等待队列 2301_82257383 程序员 java python 数据库
为什么需要等待队列实现思路代码实现1.新建BlockQueue类2.任务的添加和获取方法定义阻塞添加任务方法put编写堵塞拿取任务方法take带超时时间的阻塞添加方法offer带超时时间的阻塞获取方法poll总结✨️本系列源码均已上传仓库1321928757/Concurrent-MulThread-Demo(github.com)")✨️前言在多线程编程中,线程池是一种非常重要的工具。它可以帮助
Java多线程向阳花自开 Java学习 java 开发语言多线程
多线程Java多线程是指在一个程序中同时运行多个任务的能力。想象一下，你正在做一顿大餐，同时煮饭、炒菜、切菜。如果你只能一次做一件事，那整个过程会很慢。但如果你可以同时进行多个任务，比如在煮饭的同时切菜，这样就能节省时间。Java多线程就像这样，它允许你的程序同时处理多个任务，从而提高效率和响应速度。通俗解释：单线程：就像一个人做多件事情，但只能按顺序一个接一个地完成，比如先煮饭，然后炒菜，再切菜
Java多线程向阳花自开 Java学习 java 开发语言多线程
多线程Java多线程是指在一个程序中同时运行多个任务的能力。想象一下，你正在做一顿大餐，同时煮饭、炒菜、切菜。如果你只能一次做一件事，那整个过程会很慢。但如果你可以同时进行多个任务，比如在煮饭的同时切菜，这样就能节省时间。Java多线程就像这样，它允许你的程序同时处理多个任务，从而提高效率和响应速度。通俗解释：单线程：就像一个人做多件事情，但只能按顺序一个接一个地完成，比如先煮饭，然后炒菜，再切菜
Java笔试面试题AI答之线程（2）工程师老罗 Java笔试面试题AI答 java 面试开发语言
文章目录7.如何确保N个线程可以访问N个资源同时又不导致死锁？1.资源排序与顺序访问2.资源分配策略3.避免占用并等待4.引入超时机制5.死锁检测与解决6.使用高级并发工具7.编程实践8.Java方法可以同时即是static又是synchronized的吗?9.什么是Java多线程同步?10.解释Java中wait和sleep方法的区别？11.如何使用threaddump？如何分析Threaddu
java多线程编程-上下文切换李2牛
上下文切换（ContextSwitch）是多线程共享同一个处理器的产物。线程活性故障死锁（Deadlock）：鹬蚌相争的场景锁死：绝情花毒世界上只有一枚解药可以解除，然后这枚解药没了。中毒的人永远无法解毒。活锁：小猫试图咬自己的尾巴但是它总是追着自己的尾巴咬，始终无法咬到。活锁的外在表现是可能处于RUNNABLE状态，但是线程的任务并没有实际的进展，一直在做无用功。饥饿：某些线程始终无法获取资源，
深度分析：Java多线程，线程安全，并发包前程有光
1：synchronized（保证原子性和可见性）1.同步锁。多线程同时访问时，同一时刻只能有一个线程能够访问使synchronized修饰的代码块或方法。它修饰的对象有以下几种：修饰一个代码块，被修饰的代码块称为同步语句块，其作用的范围是大括号{}括起来的代码，作用的对象是调用这个代码块的对象修饰一个方法，被修饰的方法称为同步方法，其作用的范围是整个方法，作用的对象是调用这个方法的对象修改一个静
Java系列：Java多线程编程经典问题详解，深入解析Java多线程生命周期、死锁、活锁与饥饿、守护线程等问题码农超哥同学 Java编程 java 开发语言
多线程编程是Java语言中的一个高级主题，它在提高程序性能和响应性方面起着至关重要的作用。本文旨在帮助Java学习人员深入理解多线程的概念，并准备相关的技术面试。线程与进程在深入多线程之前，我们需要理解线程与进程的基本概念。进程是程序执行的一个实例，它拥有自己的内存空间和系统资源。而线程是进程内部的一个执行序列，是CPU调度和分派的基本单位。一个进程可以有多个线程，这些线程共享进程的资源，但每个线
Java系列：Java多线程常见面试题，Java多线程必须掌握的知识点，理解线程池、线程安全、线程并发、性能优化等常见问题才是合格的Java程序员码农超哥同学 Java编程 java 性能优化开发语言
多线程编程在Java中是一个非常重要且复杂的领域，涉及许多经典问题。也是面试过程中最常被问及的考题，如果不能掌握这些问题，将不能称为一个合格的Java编程人员。那么Java多线程都有哪些常见问题，以及必须要掌握的知识点呢？本篇文章将列举一些基本知识点。以下是一些常见的问题：线程的创建与运行：如何创建线程？有哪些方法？（例如：继承Thread类，实现Runnable接口，使用Callable和Fut
java多线程——并发数据不一致java中的解决方案台风天赋 java多线程多线程 java 并发编程
多线程并发编程线程安全主要是由于多线程并发、同时操作共享变量导致的数据不一致。至于共享变量，需要涉及到计算机体系结构的内容：因为现代计算机都一般是设置了两级甚至三级cache。以两级cache为例：假设此时有两个CUP，线程1 线程2 | | v v CUP1 CUP2 | | v v Cache1-1 Cache2-1 | V 公用c
【Java多线程】线程安全问题与解决方案 Hacynn java 开发语言笔记线程安全 jvm 安全
目录1、线程安全问题1.2、线程安全原因2、线程加锁2.1、synchronized关键字2.2、完善代码2.3、对同一个线程的加锁操作3、内容补充3.1、内存可见性问题3.2、指令重排序问题3.3、解决方法3.4、总结volatile关键字1、线程安全问题某个代码，无论是单线程下执行还是多线程下执行都不会产生bug，被称之为“线程安全”；如果在单线程下执行正确，但是多线程下会产生bug，被称之为
Java多线程系列——同步关键字飞影铠甲 Java java 数据结构开发语言 c++算法
目录一、线程安全和数据不一致性二、synchronized关键字的作用三、synchronized工作原理四、锁的级别五、synchronized的优点与缺点六、实战应用七、总结在Java中，synchronized关键字是并发编程中的一个基本构建块，用于控制多个线程对共享资源的访问，以确保数据的一致性和线程的安全。在深入研究synchronized关键字的工作原理之前，我们需要理解在多线程环境中
JAVA面试题分享五百五十一：线程池使用不当的五个坑之乎者也· JAVA 面试题分享 java 开发语言
目录坑一：线程池中异常消失问题原因解决方法优雅的进行线程池异常处理坑二：拒绝策略设置错误导致接口超时问题原因解决方法坑三：重复创建线程池导致内存溢出问题原因解决方法坑四：共用线程池执行不同类型任务导致效率低下问题原因解决方法坑五：使用ThreadLocal和线程池的不兼容问题问题原因解决方法总结线程池是Java多线程编程中的一个重要概念，它可以有效地管理和复用线程资源，提高系统的性能和稳定性。但是
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多线程练习1(卖电影票)1、继承Thread类的方式自定义开发一个MyThread类，来继承Thread类，重写run方法，定义一个ticket共享变量，表示当前卖的是第几张票，一定要使用static关键字来修饰，这样可以确保每一个线程对象都共享这一个变量。具体代码如下：MyThread类packagetest.MaiPiao.test1;/***@authoryangchenyu*@create
Java程序员，你掌握了多线程吗？（文末送书）小尘要自信 java python 开发语言多线程系统架构
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jsonp 常用java方法 (1)以jsonp的形式返回:函数名(json字符串) /*** * 用于jsonp调用 * @param map : 用于构造json数据 * @param callback : 回调的javascript方法名 * @param filters : <code>SimpleBeanPropertyFilter theFilt
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