Terracotta in Action (2)

2.  Terracotta Eclipse Plugin

    开发基于Terracotta的应用程序的最便捷的方法就是使用TerracottaEclipse Plugin。http://www.terracotta.org/web/display/docs/Eclipse+Plugin+Guide上有详细的安装说明。安装完毕后，通过Terracotta->Add Terracotta Nature可以给已有的工程增加Terracotta Nature。此外也可以通过File->New->Project->Java->Terracotta Projects->Terracotta DSO Project创建一个Terracotta工程。Terracotta工程创建完毕后，工程的根目录下会创建tc-config.xml、terracotta目录和一个Boot jar。tc-config.xml包含了所有Terracotta相关的配置信息，例如需要进行字节码加强的类、Lock相关的配置，共享对象的root、分布式方法的配置等。Terracotta目录用于保存Terracotta客户端的日志和统计信息等。Boot jar的作用会在稍后的章节里介绍。接下来通过两个例子介绍一下Terracotta Eclipse Plugin的使用。

2.1  wait/notify 
    设想某个线程A调用了某个对象obj的wait方法后被阻塞，接下来另一个线程B调用了obj的notify方法从而唤醒了线程A。这在单个JVM中是司空见惯的场景了。但是有没有设想过B线程可以在一个不同于线程A所在的JVM中调用obj的notify方法从而唤醒线程A呢？这在Terracotta的世界里也是司空见惯的场景。
    首先建立一个Terracotta工程，然后创建以下两个普通的Java类：

 package tcinaction;

 public class A {

     public static final Object OBJECT = new Object();

     public static void main(String args[]) throws InterruptedException {

         System.out.println("A is waiting on OBJECT...");
         synchronized(OBJECT) {
             OBJECT.wait();
         }
         System.out.println("A was woken up");
     }
 }


 package tcinaction;

 public class B {

     public static void main(String args[]) throws InterruptedException {

         System.out.println("B is calling A.OBJECT.notify()...");
         synchronized(A.OBJECT) {
             A.OBJECT.notify();
         }
     }
 }

 

    然后在Package Explorer中选中A，单击右键选中Terracotta->Module A.java->Instrumented，也就是令Terracotta对A类进行字节码加强。对B类也执行同样操作。接下来在A类的OBJECT静态成员变量上单击右键，选中Terracotta->Field OBJECT->Shared root,这样A类的OBJECT就成了在Terracotta中共享的对象。再接下来在A类的main方法上单击右键，选中Terracotta->Method main->Autolock，在弹出的Specify Autolock Attributes对话框中选中Write。对B类的main方法也执行相同的操作。经过了以上操作之后，tc-config.xml的内容如下:

 <?xml version="1.0" encoding="UTF-8"?>
 <con:tc-config xmlns:con="http://www.terracotta.org/config">
   <servers>
     <server host="%i" name="localhost">
       <dso-port>9510</dso-port>
       <jmx-port>9520</jmx-port>
       <data>terracotta/server-data</data>
       <logs>terracotta/server-logs</logs>
       <statistics>terracotta/cluster-statistics</statistics>
     </server>
   </servers>
   <clients>
     <logs>terracotta/client-logs</logs>
     <statistics>terracotta/client-statistics/%D</statistics>
   </clients>
   <application>
     <dso>
       <instrumented-classes>
         <include>
           <class-expression>tcinaction.A</class-expression>
         </include>
         <include>
           <class-expression>tcinaction.B</class-expression>
         </include>
       </instrumented-classes>
       <roots>
         <root>
           <field-name>tcinaction.A.OBJECT</field-name>
         </root>
       </roots>
       <locks>
         <autolock auto-synchronized="false">
           <method-expression>void tcinaction.B.main(java.lang.String[])</method-expression>
           <lock-level>write</lock-level>
         </autolock>
         <autolock auto-synchronized="false">
           <method-expression>void tcinaction.A.main(java.lang.String[])</method-expression>
           <lock-level>write</lock-level>
         </autolock>
       </locks>
     </dso>
   </application>
 </con:tc-config>

 

    最后我们来验证一下程序的运行结果。首先选中A类，单击右键Run As->Terracotta DSO Application。此时首先会启动Terracotta server，然后会启动另外一个JVM，运行A类的main方法。输出如下：
    A is waiting on OBJECT...
    接下来选中B类，单击右键Run As->Terracotta DSO Application。此时会再启动一个JVM，执行B类的main方法，相关控制台的输出如下：
    B is calling A.OBJECT.notify()...
    回到A的控制台，发现其主线程已被唤醒并执行完毕，输出如下：
    A is waiting on OBJECT...
    A was woken up

2.2  Simple Messaging 
    在这个例子中介绍一个通过LinkedBlockingQueue在不同JVM中传递数据的方法。首先创建以下两个类：

 package tcinaction;

 import java.util.concurrent.LinkedBlockingQueue;

 public class MessageProducer {

     public static final LinkedBlockingQueue<String> PIPE = new LinkedBlockingQueue<String>();

     public static void main(String args[]) throws InterruptedException {
         for(int i = 0; i < 100; i++) {
             PIPE.offer("message-" + i);
             Thread.sleep(1000);
         }
     }
 }


 package tcinaction;

 public class MessageConsumer {

     public static void main(String args[]) throws InterruptedException {

         while(true) {
             String message = MessageProducer.PIPE.take();
             System.out.println(message);
         }
     }
 }

 

    然后将MessageProducer 和 MessageConsumer配置为instrumented；各自的main方法配置为Autolock（Write）；MessageProducer的PIPE静态成员变量配置为Shared root。此时tc-config.xml的内容如下：

 <?xml version="1.0" encoding="UTF-8"?>
 <con:tc-config xmlns:con="http://www.terracotta.org/config">
   <servers>
     <server host="%i" name="localhost">
       <dso-port>9510</dso-port>
       <jmx-port>9520</jmx-port>
       <data>terracotta/server-data</data>
       <logs>terracotta/server-logs</logs>
       <statistics>terracotta/cluster-statistics</statistics>
     </server>
   </servers>
   <clients>
     <logs>terracotta/client-logs</logs>
     <statistics>terracotta/client-statistics/%D</statistics>
   </clients>
   <application>
     <dso>
       <instrumented-classes>
         <include>
           <class-expression>tcinaction.MessageProducer</class-expression>
         </include>
         <include>
           <class-expression>tcinaction.MessageConsumer</class-expression>
         </include>
       </instrumented-classes>
       <locks>
         <autolock auto-synchronized="false">
           <method-expression>void tcinaction.MessageConsumer.main(java.lang.String[])</method-expression>
           <lock-level>write</lock-level>
         </autolock>
         <autolock auto-synchronized="false">
           <method-expression>void tcinaction.MessageProducer.main(java.lang.String[])</method-expression>
           <lock-level>write</lock-level>
         </autolock>
       </locks>
       <roots>
         <root>
           <field-name>tcinaction.MessageProducer.PIPE</field-name>
         </root>
       </roots>
     </dso>
   </application>
 </con:tc-config>

 

    最后我们来验证一下程序的运行结果。首先启动MessageConsumer，单击右键Run As->Terracotta DSO Application。然后启动MessageProducer。MessageConsumer的控制台上会显示出接收到的消息：
    message-0
    message-1
    message-2