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使用Executors创建和管理线程

来源 :中华考试网 2020-12-03

  1. 类 Executors

  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。

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  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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