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Java并发编程中使用Executors类创建和管理线程的用法

1. 类 Executors
Executors类可以看做一个“工具类”。援引JDK1.6 API中的介绍:
  此包中所定义的 Executor、ExecutorService、ScheduledExecutorService、ThreadFactory 和 Callable 类的工厂和实用方法。此类支持以下各种方法:
(1)创建并返回设置有常用配置字符串的 ExecutorService 的方法。
(2)创建并返回设置有常用配置字符串的 ScheduledExecutorService 的方法。
(3)创建并返回“包装的”ExecutorService 方法,它通过使特定于实现的方法不可访问来禁用重新配置。
(4)创建并返回 ThreadFactory 的方法,它可将新创建的线程设置为已知的状态。
(5)创建并返回非闭包形式的 Callable 的方法,这样可将其用于需要 Callable 的执行方法中。
    通过这个类能够获得多种线程池的实例,例如可以调用newSingleThreadExecutor()获得单线程的ExecutorService,调 用newFixedThreadPool()获得固定大小线程池的ExecutorService,等等。拿到ExecutorService可以做的事情就比 较多了,最简单的是用它来执行Runnable对象,也可以执行一些实现了Callable<T>的对象。用Thread的start()方 法没有返回值,如果该线程执行的方法有返回值那用ExecutorService就再好不过了,可以选择submit()、invokeAll()或者 invokeAny(),根据具体情况选择合适的方法即可。
此类中提供的一些方法有:
1.1 public static ExecutorService newCachedThreadPool()
创建一个可根据需要创建新线程的线程池,但是在以前构造的线程可用时将重用它们。对于执行很多短期异步任务的程序而言,这些线程池通常可提高程序性能。
 
1.2 public static ExecutorService newFixedThreadPool(int nThreads)
创建一个可重用固定线程数的线程池,以共享的无界队列方式来运行这些线程。
 
1.3 public static ExecutorService newSingleThreadExecutor()
创建一个使用单个 worker 线程的 Executor,以无界队列方式来运行该线程。
 
这三个方法都可以配合接口ThreadFactory的实例一起使用。并且返回一个ExecutorService接口的实例。
2. 接口 ThreadFactory
根据需要创建新线程的对象。使用线程工厂就无需再手工编写对 new Thread 的调用了,从而允许应用程序使用特殊的线程子类、属性等等。
此接口最简单的实现就是:

class SimpleThreadFactory implements ThreadFactory {
  public Thread newThread(Runnable r) {
   return new Thread(r);
  }
 }

3. 接口ExecutorService
该接口提供了管理终止的方法。
4.创建标准线程池启动线程
4.1 提供一个简单的实现Runnable接口的线程
MyThread.java

package com.zj.concurrency.executors;
 
public class MyThread implements Runnable {
  private int count = 1, number;
 
  public MyThread(int num) {
    number = num;
    System.out.println("Create Thread-" + number);
  }
 
  public void run() {
    while (true) {
      System.out.println("Thread-" + number + " run " + count+" time(s)");
      if (++count == 3)
       return;
    }
  }
}

这个线程会打印出相应的创建和执行信息。
 
4.2使用CachedThreadPool启动线程
CachedThreadPool.java

package com.zj.concurrency.executors;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
 
public class CachedThreadPool {
  public static void main(String[] args) {
    ExecutorService exec = Executors.newCachedThreadPool();
    for (int i = 0; i < 5; i++)
      exec.execute(new MyThread(i));
    exec.shutdown();
  }
}

结果:

Create Thread-0
Create Thread-1
Create Thread-2
Create Thread-3
Thread-0 run 1 time(s)
Thread-0 run 2 time(s)
Thread-1 run 1 time(s)
Thread-1 run 2 time(s)
Thread-2 run 1 time(s)
Thread-2 run 2 time(s)
Create Thread-4
Thread-4 run 1 time(s)
Thread-4 run 2 time(s)
Thread-3 run 1 time(s)
Thread-3 run 2 time(s)

 
4.3 使用FixedThreadPool启动线程

FixedThreadPool.java
package com.zj.concurrency.executors;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
 
public class FixedThreadPool {
  public static void main(String[] args) {
    ExecutorService exec = Executors.newFixedThreadPool(2);
    for (int i = 0; i < 5; i++)
      exec.execute(new MyThread(i));
    exec.shutdown();
  }
}

结果:

Create Thread-0
Create Thread-1
Create Thread-2
Create Thread-3
Create Thread-4
Thread-0 run 1 time(s)
Thread-0 run 2 time(s)
Thread-2 run 1 time(s)
Thread-2 run 2 time(s)
Thread-3 run 1 time(s)
Thread-3 run 2 time(s)
Thread-4 run 1 time(s)
Thread-4 run 2 time(s)
Thread-1 run 1 time(s)
Thread-1 run 2 time(s)

 
4.4 使用SingleThreadExecutor启动线程
SingleThreadExecutor.java

package com.zj.concurrency.executors;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
 
public class SingleThreadExecutor {
  public static void main(String[] args) {
    ExecutorService exec = Executors.newSingleThreadExecutor();
    for (int i = 0; i < 5; i++)
      exec.execute(new MyThread(i));
    exec.shutdown();
  }
}

结果:

Create Thread-0
Create Thread-1
Create Thread-2
Create Thread-3
Create Thread-4
Thread-0 run 1 time(s)
Thread-0 run 2 time(s)
Thread-1 run 1 time(s)
Thread-1 run 2 time(s)
Thread-2 run 1 time(s)
Thread-2 run 2 time(s)
Thread-3 run 1 time(s)
Thread-3 run 2 time(s)
Thread-4 run 1 time(s)
Thread-4 run 2 time(s)

5.配合ThreadFactory接口的使用
我们试图给线程加入daemon和priority的属性设置。
5.1设置后台线程属性
DaemonThreadFactory.java

package com.zj.concurrency.executors.factory;
import java.util.concurrent.ThreadFactory;
 
public class DaemonThreadFactory implements ThreadFactory {
  public Thread newThread(Runnable r) {
    Thread t = new Thread(r);
    t.setDaemon(true);
    return t;
  }
}

 
5.2 设置优先级属性
最高优先级MaxPriorityThreadFactory.java

package com.zj.concurrency.executors.factory;
import java.util.concurrent.ThreadFactory;
 
public class MaxPriorityThreadFactory implements ThreadFactory {
  public Thread newThread(Runnable r) {
    Thread t = new Thread(r);
    t.setPriority(Thread.MAX_PRIORITY);
    return t;
  }
}

最低优先级MinPriorityThreadFactory.java

package com.zj.concurrency.executors.factory;
import java.util.concurrent.ThreadFactory;
 
public class MinPriorityThreadFactory implements ThreadFactory {
  public Thread newThread(Runnable r) {
    Thread t = new Thread(r);
    t.setPriority(Thread.MIN_PRIORITY);
    return t;
  }
}

 
5.3启动带有属性设置的线程
ExecFromFactory.java

package com.zj.concurrency.executors;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import com.zj.concurrency.executors.factory.DaemonThreadFactory;
import com.zj.concurrency.executors.factory.MaxPriorityThreadFactory;
import com.zj.concurrency.executors.factory.MinPriorityThreadFactory;
 
public class ExecFromFactory {
  public static void main(String[] args) throws Exception {
    ExecutorService defaultExec = Executors.newCachedThreadPool();
    ExecutorService daemonExec = Executors
       .newCachedThreadPool(new DaemonThreadFactory());
    ExecutorService maxPriorityExec = Executors
       .newCachedThreadPool(new MaxPriorityThreadFactory());
    ExecutorService minPriorityExec = Executors
       .newCachedThreadPool(new MinPriorityThreadFactory());
    for (int i = 0; i < 10; i++)
      daemonExec.execute(new MyThread(i));
    for (int i = 10; i < 20; i++)
      if (i == 10)
       maxPriorityExec.execute(new MyThread(i));
      else if (i == 11)
       minPriorityExec.execute(new MyThread(i));
      else
       defaultExec.execute(new MyThread(i));
  }
}

结果:

Create Thread-0
Create Thread-1
Create Thread-2
Create Thread-3
Thread-0 run 1 time(s)
Thread-0 run 2 time(s)
Thread-1 run 1 time(s)
Thread-1 run 2 time(s)
Thread-2 run 1 time(s)
Thread-2 run 2 time(s)
Create Thread-4
Thread-4 run 1 time(s)
Thread-4 run 2 time(s)
Create Thread-5
Thread-5 run 1 time(s)
Thread-5 run 2 time(s)
Create Thread-6
Create Thread-7
Thread-7 run 1 time(s)
Thread-7 run 2 time(s)
Create Thread-8
Thread-8 run 1 time(s)
Thread-8 run 2 time(s)
Create Thread-9
Create Thread-10
Thread-10 run 1 time(s)
Thread-10 run 2 time(s)
Create Thread-11
Thread-9 run 1 time(s)
Thread-9 run 2 time(s)
Thread-6 run 1 time(s)
Thread-6 run 2 time(s)
Thread-3 run 1 time(s)
Thread-3 run 2 time(s)
Create Thread-12
Create Thread-13
Create Thread-14
Thread-12 run 1 time(s)
Thread-12 run 2 time(s)
Thread-13 run 1 time(s)
Thread-13 run 2 time(s)
Create Thread-15
Thread-15 run 1 time(s)
Thread-15 run 2 time(s)
Create Thread-16
Thread-16 run 1 time(s)
Thread-16 run 2 time(s)
Create Thread-17
Create Thread-18
Create Thread-19
Thread-14 run 1 time(s)
Thread-14 run 2 time(s)
Thread-17 run 1 time(s)
Thread-17 run 2 time(s)
Thread-18 run 1 time(s)
Thread-18 run 2 time(s)
Thread-19 run 1 time(s)
Thread-19 run 2 time(s)
Thread-11 run 1 time(s)
Thread-11 run 2 time(s)

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