Java线程总结
fmms
13年前
<p class="MsoNormal"><span>今天准备总结一下关于<span lang="EN-US">Java</span> 线程的问题，提到线程很容易与进程混淆，从计算机操作系统的发展来看，经历了这样的两个阶段：</span> </p> <p class="MsoNormal"><span><span> </span></span><span>单进程处理：最早以前的<span lang="EN-US">DOS</span> 系统就属于单进程处理，即：在同一个时间段上只能有一个程序在执行，所以在<span lang="EN-US">DOS</span> 系统中只要有病毒的出现，则立刻会有反映；</span> </p> <p class="MsoNormal"><span><span> </span></span><span>多进程处理：我们现在使用的<span lang="EN-US">Windows</span> 操作系统就是典型的一个多线程，所以，如果在<span lang="EN-US">windows</span> 中出现病毒了，则系统照样可以使用，通过<span lang="EN-US">Ctrl+Shift+delete</span> 可以查看<span lang="EN-US">windows</span> 系统的具体进程情况；</span> </p> <p class="MsoNormal"><span><span> </span></span><span>那么对于资源来讲，所有的<span lang="EN-US">IO</span> 设备、<span lang="EN-US">CPU</span> 等等只有一个，那么对于多线程的处理来讲，在<strong><span style="color:red;">同一个时间段</span> </strong>上会有多个程序运行，但是在<strong><span style="color:red;">同一个时间点</span> </strong>上只能有一个程序运行。所以我们可以发现线程是在进程的基础上进一步的划分，我们可以举个这样的例子，<span lang="EN-US">Eclipse</span> 中对<span lang="EN-US">Java</span> 的关键字的检查，是在<span lang="EN-US">Eclipse</span> 整个程序运行中检测运行的。因此进程中止了，线程也随之中止。但是线程中止了，进程可能依然会执行。我们可以这样理解，进程是一个静态的概念，一个任务或者说一个程序，一个进程里有一个主线程。</span> </p> <p class="MsoNormal"><span><span> </span></span><span>下面我们来看看<span lang="EN-US">Java</span> 中对线程处理机制的支持，在<span lang="EN-US">Java</span> 语言中对线程的实现有两种方恨死：一个是继承<span lang="EN-US">Thread</span> 类，另一个是实现<span lang="EN-US">Runnable</span> 接口。下面我们来分别来看看这两种实现方式：<span lang="EN-US"><span> </span></span></span></p> <p class="MsoNormal"><strong><span>继承<span lang="EN-US">Thread</span> 类：</span> </strong></p> <p class="MsoNormal"><span><span> </span></span><span>一个<span lang="EN-US">java</span> 类只要继承了<span lang="EN-US">Thread</span> 类<span lang="EN-US"><span> </span></span>，同时覆写了本类中的<span lang="EN-US">run()</span> 方法，则就可以实现<span lang="EN-US">Java</span> 中的多线程操作了。</span> </p> <p><span>MyThread.java</span> <span>：</span></p> <pre class="brush:java; toolbar: true; auto-links: false;">package com.iflytek.thread; /** * @author xudongwang 2012-1-1 * * Email:xdwangiflytek@gmail.com */ public class MyThread extends Thread { private String name; public MyThread(String name) { this.name = name; } public void run() {// 覆写run()方法 for (int i = 0; i < 10; i++) { System.out.println("Thread运行:" + name + ",i=" + i); } } }</pre> <span>下面我们来实现上面的多线程操作类，<span lang="EN-US">MyThreadTest.java</span> ：<pre class="brush:java; toolbar: true; auto-links: false;">package com.iflytek.thread; /** * @author xudongwang 2012-1-1 * * Email:xdwangiflytek@gmail.com */ public class MyThreadTest { public static void main(String[] args) { MyThread thread1 = new MyThread("线程A"); MyThread thread2 = new MyThread("线程B"); thread1.run();// 调用线程 thread2.run(); } }</pre></span> <p></p> <p class="MsoNormal"><span>通过运行结果，我们可以发现其执行的结果非常有规律，先执行完第一个对象，再执行完第二个对象的，即没有实现交互的现象；</span> </p> <p style="text-indent:21pt;" class="MsoNormal"><span>通过<span lang="EN-US">JDK</span> 文档可以发现，一旦我们调用<span lang="EN-US">Start()</span> 方法，则会通过<span lang="EN-US">JVM</span> 找到<span lang="EN-US">run()</span> 方法。所以当我们将上面调用的<span lang="EN-US">run()</span> 方法改为<span lang="EN-US">start()</span> 方法：</span></p> <pre class="brush:java; toolbar: true; auto-links: false;">package com.iflytek.thread; /** * @author xudongwang 2012-1-1 * * Email:xdwangiflytek@gmail.com */ public class MyThreadTest { public static void main(String[] args) { MyThread thread1 = new MyThread("线程A"); MyThread thread2 = new MyThread("线程B"); thread1.start();// 调用线程 thread2.start(); } }</pre> <span>这时再去执行发现结果有交互的现象，所以这也值得我们思考为什么非要使用<span lang="EN-US">start()</span> 方法启动多线程呢？通过查看<span lang="EN-US">Java</span> 源码<span lang="EN-US">:<pre class="brush:java; toolbar: true; auto-links: false;">public synchronized void start() {//定义start方法 /** * This method is not invoked for the main method thread or "system" * group threads created/set up by the VM. Any new functionality added * to this method in the future may have to also be added to the VM. * * A zero status value corresponds to state "NEW". */ if (threadStatus != 0 || this != me)//判断线程是否已经启动 throw new IllegalThreadStateException(); group.add(this); start0();//调用start0方法 if (stopBeforeStart) { stop0(throwableFromStop); } } private native void start0();//使用native关键字声明的方法没有方法体</pre></span></span> <p></p> <p class="MsoNormal"><span>说明：操作系统有很多种，<span lang="EN-US">Windows</span> 、<span lang="EN-US">Linux</span> 、<span lang="EN-US">UNIX</span> ，既然多线程操作中要进行<span lang="EN-US">CPU</span> 资源的强占，也就是说要等待<span lang="EN-US">CPU</span> 调度，那么这些调度的操作是由各个操作系统的底层实现的，所以在<span lang="EN-US">Java</span> 程序中根本就没法实现，那么此时<span lang="EN-US">Java</span> 的设计者定义了<span lang="EN-US">native</span> 关键字，使用此关键字表示可以调用操作系统的底层函数，那么这样的技术又称为<span lang="EN-US">JNI</span> 技术（<span lang="EN-US">Java Native Interface</span> ），而且，此方法在执行的时候将调用<span lang="EN-US">run</span> 方法完成，由系统默认调用的。</span> </p> <p class="MsoNormal"><span>下面我们看看线程的状态：</span> </p> <p><img title="7751f5b5-0065-3e0f-aa81-c8f5db51e8f3.png" border="0" alt="7751f5b5-0065-3e0f-aa81-c8f5db51e8f3.png" src="https://simg.open-open.com/show/e4b371e09575e7a6407b9ab9433a1d50.png" width="402" height="203" /></p> <p> </p> <p class="MsoNormal"><strong><span>实现<span lang="EN-US">Runnable</span> 接口：</span> </strong></p> <p class="MsoNormal"><span><span> </span></span><span>因为我们知道继承的单一继承的局限性，所以我们在开发中一个多线程的操作类很少去使用<span lang="EN-US">Thread</span> 类完成，而是通过<span lang="EN-US">Runnable</span> 接口完成。</span> </p> <p> </p> <p class="MsoNormal"><span> 查看源码发现<span lang="EN-US">Runnable</span> 的定义：</span></p> <pre class="brush:java; toolbar: true; auto-links: false;"> public interface Runnable { public abstract void run(); }</pre> <span>所以一个类只要实现了此接口，并覆写<span lang="EN-US">run()</span> 方法<pre class="brush:java; toolbar: true; auto-links: false;">package com.iflytek.thread; /** * * @author xudongwang 2012-1-1 * * Email:xdwangiflytek@gmail.com */ public class MyThreadByRunnable implements Runnable { private String name; public MyThreadByRunnable(String name) { this.name = name; } public void run() {// 覆写run()方法 for (int i = 0; i < 10; i++) { System.out.println("Thread运行:" + name + ",i=" + i); } } }</pre></span> <span>有了多线程操作类下面我们需要启动多线程，但是在现在使用<span lang="EN-US">Runnable</span> 定义的子类中并没有<span lang="EN-US">start()</span> 方法，而只有<span lang="EN-US">Thread</span> 类中才有，在<span lang="EN-US">Thread</span> 类中存在以下的一个构造方法：<pre class="brush:java; toolbar: true; auto-links: false;"> public Thread(Runnable target) { init(null, target, "Thread-" + nextThreadNum(), 0); }</pre></span> <span>此构造方法接受<span lang="EN-US">Runnable</span> 的子类实例，也就是说现在我们可以通过<span lang="EN-US">Thread</span> 类来启动<span lang="EN-US">Runnable</span> 实现的多线程。<pre class="brush:java; toolbar: true; auto-links: false;">package com.iflytek.thread; /** * * @author xudongwang 2012-1-1 * * Email:xdwangiflytek@gmail.com */ public class MyThreadByRunnableTest { public static void main(String[] args) { MyThreadByRunnable thread1 = new MyThreadByRunnable("线程A"); MyThreadByRunnable thread2 = new MyThreadByRunnable("线程B"); new Thread(thread1).start(); new Thread(thread2).start(); } }</pre></span> <p></p> <p class="MsoNormal"><span>当然上面的操作代码也属于交替的运行，所以此时程序也同样实现了多线的操作；</span> </p> <p class="MsoNormal"><span> </span> </p> <p class="MsoNormal"><span>下面我们来总结一下两种实现方式的区别及联系：</span> </p> <p class="MsoNormal"><span><span> </span></span><span>在程序的开发中只要是多线程则肯定永远以实现<span lang="EN-US">Runnable</span> 接口为正统操作，因为实现<span lang="EN-US">Runnable</span> 接口相比继承<span lang="EN-US">Thread</span> 类有如下的好处：</span> </p> <p class="MsoListParagraph"><strong><span><span>1、<span style="line-height:normal;font-variant:normal;font-style:normal;font-size:7pt;font-weight:normal;"> </span></span></span></strong><strong><span>避免单继承的局限性，一个类可以同时实现多个接口</span> </strong></p> <p class="MsoListParagraph"><strong><span><span>2、<span style="line-height:normal;font-variant:normal;font-style:normal;font-size:7pt;font-weight:normal;"> </span></span></span></strong><strong><span>适合于资源的共享</span> </strong></p> <p class="MsoNormal"><span> </span> </p> <p class="MsoNormal"><span>下面来说说关于线程的几个<span lang="EN-US">Demo</span> ；</span> </p> <p class="MsoNormal"><span>1</span> <span>、两个线程访问同一个对象，<span lang="EN-US">ThreadSyncDemo.java</span> ：</span></p> <pre class="brush:java; toolbar: true; auto-links: false;">package com.iflytek.thread; /** * @author xudongwang 2012-1-1 * * Email:xdwangiflytek@gmail.com */ public class ThreadSyncDemo implements Runnable { Timer timer = new Timer(); public static void main(String[] args) { ThreadSyncDemo threadSyncDemo = new ThreadSyncDemo(); Thread thread1 = new Thread(threadSyncDemo); Thread thread2 = new Thread(threadSyncDemo); thread1.setName("t1");// 修改线程名称 thread2.setName("t2"); thread1.start(); thread2.start(); } @Override public void run() { timer.add(Thread.currentThread().getName()); } } class Timer { private static int num = 0; public void add(String name) { num++; try { // 第一个线程执行到 这里时被休眠了，这是num为1，而第二个线程重新来执行时num为2，并休眠，而此时第一个线程启动了 Thread.sleep(1); } catch (InterruptedException e) { } System.out.println(name + ",你是第" + num + "个使用timer的线程"); } }</pre> <p></p> <p class="MsoNormal"><span>运行结果：</span> </p> <table style="border-bottom:medium none;border-left:medium none;border-collapse:collapse;border-top:medium none;border-right:medium none;" class="MsoTableGrid" border="1" cellspacing="0" cellpadding="0"> <tbody> <tr> <td style="padding-bottom:0cm;padding-left:5.4pt;width:426.1pt;padding-right:5.4pt;padding-top:0cm;" valign="top" width="568"> <p style="text-align:left;" class="MsoNormal" align="left"><span style="font-family:Consolas;color:black;font-size:10pt;">t1,</span> <span>你是第</span> <span style="font-family:Consolas;color:black;font-size:10pt;">2</span> <span>个使用</span> <span style="font-family:Consolas;color:black;font-size:10pt;">timer</span> <span>的线程</span> </p> <p class="MsoNormal"><span style="font-family:Consolas;color:black;font-size:10pt;">t2,</span> <span>你是第</span> <span style="font-family:Consolas;color:black;font-size:10pt;">2</span> <span>个使用</span> <span style="font-family:Consolas;color:black;font-size:10pt;">timer</span> <span>的线程</span> </p> </td> </tr> </tbody> </table> <p class="MsoNormal"><span>而如果程序这样改动一下，<span lang="EN-US">ThreadSyncDemo02.java</span> ：</span></p> <pre class="brush:java; toolbar: true; auto-links: false;">package com.iflytek.thread; /** * @author xudongwang 2012-1-1 * * Email:xdwangiflytek@gmail.com */ public class ThreadSyncDemo02 implements Runnable { Timer02 timer = new Timer02(); public static void main(String[] args) { ThreadSyncDemo02 threadSyncDemo = new ThreadSyncDemo02(); Thread thread1 = new Thread(threadSyncDemo); Thread thread2 = new Thread(threadSyncDemo); thread1.setName("t1");// 修改线程名称 thread2.setName("t2"); thread1.start(); thread2.start(); } @Override public void run() { timer.add(Thread.currentThread().getName()); } } class Timer02 { private static int num = 0; public synchronized void add(String name) {// 执行这个方法的过程之中，当前对象被锁定 synchronized (this) {// 这样的话，在｛｝中的线程执行的过程中不会被另一个线程打断，也就是说｛｝只能有一个线程 num++; try { Thread.sleep(1);// 第一个线程执行到 // 这里时被休眠了，这是num为1，而第二个线程重新来执行时num为2，并休眠，而此时第一个线程启动了 } catch (InterruptedException e) { } System.out.println(name + ",你是第" + num + "个使用timer的线程"); } } }</pre> <span>运行结果：</span> <p></p> <table style="border-bottom:medium none;border-left:medium none;border-collapse:collapse;border-top:medium none;border-right:medium none;" class="MsoTableGrid" border="1" cellspacing="0" cellpadding="0"> <tbody> <tr> <td style="padding-bottom:0cm;padding-left:5.4pt;width:426.1pt;padding-right:5.4pt;padding-top:0cm;" valign="top" width="568"> <p style="text-align:left;" class="MsoNormal" align="left"><span style="font-family:Consolas;color:black;font-size:10pt;">t1,</span> <span>你是第</span> <span style="font-family:Consolas;color:black;font-size:10pt;">1</span> <span>个使用</span> <span style="font-family:Consolas;color:black;font-size:10pt;">timer</span> <span>的线程</span> </p> <p class="MsoNormal"><span style="font-family:Consolas;color:black;font-size:10pt;">t2,</span> <span>你是第</span> <span style="font-family:Consolas;color:black;font-size:10pt;">2</span> <span>个使用</span> <span style="font-family:Consolas;color:black;font-size:10pt;">timer</span> <span>的线程</span> </p> </td> </tr> </tbody> </table> <p class="MsoNormal"><span> </span> </p> <p class="MsoNormal"><span>2</span> <span>、死锁，<span lang="EN-US">ThreadDieDemo.java</span> ：</span></p> <pre class="brush:java; toolbar: true; auto-links: false;">package com.iflytek.thread; /** * @author xudongwang 2012-1-1 * * Email:xdwangiflytek@gmail.com */ public class ThreadDieDemo { public static void main(String[] args) { DeadLock lock1 = new DeadLock(); DeadLock lock2 = new DeadLock(); lock1.flag = 1; lock2.flag = 2; Thread thread1 = new Thread(lock1); Thread thread2 = new Thread(lock2); thread1.start(); thread2.start(); } } class DeadLock implements Runnable { public int flag = 1; static Object o1 = new Object(); static Object o2 = new Object(); @Override public void run() { System.out.println("flag = " + flag); if (flag == 1) { synchronized (o1) { try { Thread.sleep(500); } catch (InterruptedException e) { e.printStackTrace(); } synchronized (o2) { System.out.println("o2"); } } } if (flag == 2) { synchronized (o2) { try { Thread.sleep(500); } catch (InterruptedException e) { e.printStackTrace(); } synchronized (o1) { System.out.println("o1"); } } } } }</pre> <p></p> <p class="MsoNormal"><span>3</span> <span>、生产者和消费者问题：</span> </p> <p class="MsoNormal"><span>首先简单说明一下<span lang="EN-US">sleep</span> 、<span lang="EN-US">wait</span> 、<span lang="EN-US">notify</span> 的区别：</span> </p> <p class="MsoNormal"><span><span> </span>sleep</span> <span>：<span lang="EN-US">sleep</span> 是在<span lang="EN-US">Thread</span> 中的，同时在<span lang="EN-US">sleep</span> 的时候锁还在；</span> </p> <p class="MsoNormal"><span> wait</span> <span>：<span lang="EN-US">wait</span> 必须是在锁住对象时才能<span lang="EN-US">wait</span> ，同时在<span lang="EN-US">wait</span> 的时候，锁就不在归那个对象所有了，而在其方法定义在<span lang="EN-US">Object</span> 中，它是让进入到此锁住对象的线程<span lang="EN-US">wait</span> ；</span> </p> <p style="text-indent:21pt;" class="MsoNormal"><span>notify</span> <span>：与<span lang="EN-US">wait</span> 相对应，叫醒一个现在正在<span lang="EN-US">wait</span> 在我这个对象上的线程，谁现在正在我这个对象上等待，我就叫醒这个线程让他继续执行，他也是<span lang="EN-US">Object</span> 类中的方法；</span> </p> <p style="text-indent:21pt;" class="MsoNormal"><span>ProductCustomerDemo.java</span> <span>：</span></p> <pre class="brush:java; toolbar: true; auto-links: false;">package com.iflytek.thread; /** * @author xudongwang 2012-1-1 * * Email:xdwangiflytek@gmail.com */ public class ProductCustomerDemo { public static void main(String[] args) { WoToStack woToStack = new WoToStack(); Product product = new Product(woToStack); Customer customer = new Customer(woToStack); new Thread(product).start(); new Thread(customer).start(); } } /** * 消费和生产的对象 * * @author xudongwang 2012-1-1 * * Email:xdwangiflytek@gmail.com */ class WoTo { int id; public WoTo(int id) { this.id = id; } @Override public String toString() { return "WoTo [id=" + id + "]"; } } class WoToStack { int index = 0; WoTo[] arrayWoTo = new WoTo[10];// 这里限制一下，框子最多装10个WoTo /** * 向框子中放WoTo * * @param wt */ public synchronized void push(WoTo wt) { // 这里用while是因为如果被打断还要执行判断，而如果是if则会直接进入下一个语句 while (index == arrayWoTo.length) { try { this.wait(); } catch (InterruptedException e) { e.printStackTrace(); } } this.notifyAll(); arrayWoTo[index] = wt; index++; } /** * 从框子中去WoTo * * @return */ public synchronized WoTo pop() { while (index == 0) { try { this.wait(); } catch (InterruptedException e) { e.printStackTrace(); } } this.notifyAll(); index--; return arrayWoTo[index]; } } /** * 生产者 * * @author xudongwang 2012-1-1 * * Email:xdwangiflytek@gmail.com */ class Product implements Runnable { // 首先生产者需要知道生产WoTo放在哪里 WoToStack stack = null; public Product(WoToStack stack) { this.stack = stack; } @Override public void run() { for (int i = 0; i < 20; i++) {// 这里我们限制一下每一个生产者可以生产20个WoTo WoTo woTo = new WoTo(i); stack.push(woTo); System.out.println("生产者生产了 ：" + woTo); try { Thread.sleep((int) Math.random() * 200); } catch (InterruptedException e) { e.printStackTrace(); } } } } class Customer implements Runnable { WoToStack stack = null; public Customer(WoToStack stack) { this.stack = stack; } @Override public void run() { for (int i = 0; i < 20; i++) {// 这里我们也限制一下每一个小费者可以消费20个WoTo WoTo woTo = stack.pop(); System.out.println("消费者消费了 ：" + woTo); try { Thread.sleep((int) Math.random() * 1000); } catch (InterruptedException e) { e.printStackTrace(); } } } }</pre> <p></p> <p class="MsoNormal"><span>4</span> <span>、卖票问题（<span lang="EN-US">Runnable</span> 资源共享）：</span> </p> <p class="MsoNormal"><span>MyThread.java:</span></p> <pre class="brush:java; toolbar: true; auto-links: false;">package com.iflytek.maipiao; /** * @author xudongwang 2012-1-1 * * Email:xdwangiflytek@gmail.com */ public class MyThread extends Thread { private int ticket = 5;// 一共5张票 public void run() { for (int i = 0; i < 50; i++) { if (this.ticket > 0) { System.out.println("卖票：ticket = " + this.ticket--); } } } }</pre> <span>下面建三个线程对象，同时卖票，<span lang="EN-US">ThreadTicket.java</span> ：<pre class="brush:java; toolbar: true; auto-links: false;">package com.iflytek.maipiao; /** * @author xudongwang 2012-1-1 * * Email:xdwangiflytek@gmail.com */ public class ThreadTicket { public static void main(String[] args) { MyThread thread1 = new MyThread(); MyThread thread2 = new MyThread(); MyThread thread3 = new MyThread(); // 开始卖票 thread1.start(); thread2.start(); thread3.start(); } }</pre></span> <p class="MsoNormal"><span>运行发现一共卖了<span lang="EN-US">15</span> 张票，但是实际上只有<span lang="EN-US">5</span> 张票，所以证明每一个线程都卖自己的票，这样就没有达到资源共享的目的。</span> </p> <p class="MsoNormal"><span>其实我们使用<span lang="EN-US">Runnable</span> 接口的话，则就可以实现资源的共享：</span> </p> <p class="MsoNormal"><span>MyThreadByRunnable.java</span> <span>：</span></p> <pre class="brush:java; toolbar: true; auto-links: false;">package com.iflytek.maipiao; /** * @author xudongwang 2012-1-1 * * Email:xdwangiflytek@gmail.com */ public class MyThreadByRunnable implements Runnable { private int ticket = 5;// 一共5张票 public void run() { for (int i = 0; i < 50; i++) { if (this.ticket > 0) { System.out.println("卖票：ticket = " + this.ticket--); } } } }</pre> <span>同样，我们再弄一个多线程进行卖票的操作，<span lang="EN-US">RunnableTicket.Java</span> ：<pre class="brush:java; toolbar: true; auto-links: false;">package com.iflytek.maipiao; /** * @author xudongwang 2012-1-1 * * Email:xdwangiflytek@gmail.com */ public class RunnableTicket { public static void main(String[] args) { MyThreadByRunnable threadByRunnable = new MyThreadByRunnable(); new Thread(threadByRunnable).start(); new Thread(threadByRunnable).start(); new Thread(threadByRunnable).start(); } }</pre></span> <p></p> <p class="MsoNormal"><span>虽然现在程序中有三个线程，但是从运行结果上看，三个线程一共卖出了<span lang="EN-US">5</span> 张票，也就是说使用<span lang="EN-US">Runnable</span> 实现的多线程可以达到资源共享的目的。</span> </p> <p class="MsoNormal"><span>实际上，<span lang="EN-US">Runnable</span> 接口和<span lang="EN-US">Thread</span> 类之间还是存在联系的</span></p> <pre class="brush:java; toolbar: true; auto-links: false;">Public class Thread implements Runnable {</pre> <p></p> <p class="MsoNormal"><span>发现<span lang="EN-US">Thread</span> 类也是<span lang="EN-US">Runnable</span> 接口的子类。</span> </p> <p class="MsoNormal"><span>在实际的开发中比如说发多个邮件提醒等都会用到线程的，所以线程还是很重要的；<br /> <br /> 转自：<a href="/misc/goto?guid=4959500212274664494" target="_blank">http://xdwangiflytek.iteye.com/blog/1333128</a></span> </p> <p class="MsoNormal"></p> <p class="MsoNormal"></p> <p></p> <p style="text-indent:21pt;" class="MsoNormal"></p> <p class="MsoNormal"></p> <p class="MsoNormal"></p> <p class="MsoNormal"></p> <p class="MsoNormal"></p> <p style="text-indent:21pt;" class="MsoNormal"></p> <p></p>