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Java:测试服务的并发性
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Stack Overflow用户
提问于 2019-05-14 02:59:17
回答 1查看 159关注 0票数 1

我有一个服务类,其中包含向Section添加Student的方法。现在,每个Section都有一个与之关联的set Students

此外,还有一个Map<Section, Set<Student>>定义了两者之间的关系。

使用addStudent方法时,service如下所示:

public class MembershipService {

private final Map<Section, Set<Student>> studentsBySection = new HashMap<>();


public void addStudentToSection(Student student, Section sec) {

 Set<Student> students = studentsBySection.get(sec);
    if (students == null) {
        students = new HashSet<>();
        studentsBySection.put(sec, students);
    }
    students.add(student);

}
//  ..... also containing helper method : getStudents(Section s)

我需要在多线程场景中测试功能,其中我需要展示如果两个或更多线程试图从公共map添加或读取学生会发生什么。

我清楚地知道用ConcurrentHashMap替换Hashmap会解决我的问题,但是我不能演示确切的行为。

My Solution

我创建了两个线程:Student1Student2,并尝试将相同的Service实例传递给这两个线程并执行添加操作。hashmap的预期行为应该是ConcurrentModificationException,而ConcurrentHashMap则不应该抛出。但它没有显示出预期的行为,即使使用HashMap也能很好地工作。请指点一下。

代码如下:

Student1

public class Student1 implements Runnable{

Services services;

public Student1(Services ser) {
    this.services =  ser;
    new Thread(this, "Student 1").start();
}



@Override
public void run() {
    final Student ALEX = new Student("alex");


    services.getMembershipService().addStudentToSection(ALEX,services.getSection());;

    try {
        System.out.println("Student 1 sleeping");
        Thread.sleep(100);
    } catch (Exception e) {
        System.out.println(e);
    }

}

}

Student2

  public class Student2 implements Runnable{

Services services;

public Student2(Services ser) {
    this.services =  ser;
    new Thread(this, "Student 2").start();
}



@Override
public void run() {
    final Student JOHN = new Student("john");


    services.getMembershipService().addStudentToSection(JOHN,services.getSection());;

    try {
        System.out.println("Student 2 sleeping");
        Thread.sleep(100);
    } catch (Exception e) {
        System.out.println(e);
    }

}

}

Tester.java

public static void main(String[] args) {
    final Services services = ServiceFactory.createServices();
    final Section A = new Section("A");
    services.createSection(A);

    Student1 one = new Student1(services);
    Student2 two = new Student2(services);

}

我该如何证明我的案子?

注意:这不是关于How ConcurrentHashMap works in java或general.Am中的多线程,知道这一点。我只是不能让它与我的需求保持一致。

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回答 1

Stack Overflow用户

发布于 2019-05-14 03:29:25

您的HashMap和ConcurrentHashMap在多线程环境中工作相同的原因是由于输入较少。我同时放入和读取200个键值对。

只需在代码中将ConcurrentHashMap替换为HashMap,即可获得concurrentModificationException。

ConcurrentHashMap实现:

package com.java.ConcurrentHashMap;

import java.util.HashMap;
import java.util.HashSet;
import java.util.Iterator;
import java.util.Set;
import java.util.concurrent.ConcurrentHashMap;
public class ConcurrentHashMapDemo {


    private  final ConcurrentHashMap<Section,Set<Student>> studentsBySection = new ConcurrentHashMap<>();

    public  void addStudentToSection(Student student, Section sec) {
//System.out.println(Thread.currentThread().getName());
         Set<Student> students = studentsBySection.get(sec);
            if (students == null) {
                students = new HashSet<>();
                studentsBySection.putIfAbsent(sec, students);
            }
            students.add(student);

        }




      public static void main(String[] args) {
          ConcurrentHashMapDemo ob = new ConcurrentHashMapDemo();



          Thread t1 = new Thread(ob.new WriteThreasOne());
          t1.setName("one");

          Thread t3 = new Thread(ob.new WriteThreasTwo());
          t3.setName("three");
          Thread t2= new Thread(ob.new ReadThread());
          t2.setName("two");
          t1.start();
          t2.start();
          t3.start();
      }
      class WriteThreasOne implements Runnable {
        @Override
        public void run() {


            final Section A = new Section("A");

            for(int i=0;i<100;i++) {
                addStudentToSection(new Student("alex"+i),A);
            }




        }
      }
      class WriteThreasTwo implements Runnable {
        @Override
        public void run() {


            final Section A = new Section("A");
            for(int i=1;i<100;i++) {
                addStudentToSection(new Student("sam"+i),A);
            }


        }
      }  
      class ReadThread implements Runnable {
        @Override
        public void run() {
            //System.out.println(Thread.currentThread().getName());

           Iterator<Section> ite = studentsBySection.keySet().iterator();
           while(ite.hasNext()){
               Section key = ite.next();
               System.out.println(key+" : " + studentsBySection.get(key));
          }
        }
      }   
}

部分类:

package com.java.ConcurrentHashMap;

public class Section {

    public Section(String sectionName) {
        this.sectionName = sectionName;
    }

    private String sectionName;



    public String getSectionName() {
        return sectionName;
    }

    public void setSectionName(String sectionName) {
        this.sectionName = sectionName;
    }

    @Override
    public String toString() {
        return "Section [sectionName=" + sectionName + "]";
    }

    @Override
    public int hashCode() {
        final int prime = 31;
        int result = 1;
        result = prime * result + ((sectionName == null) ? 0 : sectionName.hashCode());
        return result;
    }

    @Override
    public boolean equals(Object obj) {
        if (this == obj)
            return true;
        if (obj == null)
            return false;
        if (getClass() != obj.getClass())
            return false;
        Section other = (Section) obj;
        if (sectionName == null) {
            if (other.sectionName != null)
                return false;
        } else if (!sectionName.equals(other.sectionName))
            return false;
        return true;
    }



}

学生类:

package com.java.ConcurrentHashMap;

public class Student {



    private String studName;

    public Student(String studName) {

        this.studName = studName;
    }

    public String getStudName() {
        return studName;
    }

    public void setStudName(String studName) {
        this.studName = studName;
    }

    @Override
    public String toString() {
        return "Student [ studName=" + studName + "]";
    }

}
票数 0
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页面原文内容由Stack Overflow提供。腾讯云小微IT领域专用引擎提供翻译支持
原文链接:

https://stackoverflow.com/questions/56118386

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