JBossWeb/Tomcat 初始化连接器和处理 Http 请求过程

JBossWeb 是JBoss 中的 Web 容器，他是对 Tomcat 的封装，本文以 Http 连接器为例，简单说明 JBossWeb/Tomcat 初始化连接器和处理 Http 请求过程 。本文内容提要：

• Connector 初始化开始过程
• 如何理解 max-connections
• JIoEndpoint 处理 Socket 请求

Connector 初始化开始过程

如下图所示：

1. WebConnectorService 指的是 `org.jboss.as.web.WebConnectorService`
2. Connector 指的是 `org.apache.catalina.connector.Connector`
   
3. Http11Protocol 指的是 `org.apache.coyote.http11.Http11Protocol`
   
4. JIoEndpoint 指的是 `org.apache.tomcat.util.net.JIoEndpoint`
   

Connector init()

Connector 可以是 HTTP Connector，也可以是 AJP Connector，Connector 中有 ProtocolHandler 和 Adapter 属性，Connector 初始化主要包括：初始化 Adapter，且将初始化的 Adapter 的 设定给 ProtocolHandler，然后调运 ProtocolHandler 的初始化方法，如下面代码段所示：

[java] view plain copy print?

1. // Initializa adapter 
2. adapter = new CoyoteAdapter(this); 
3. protocolHandler.setAdapter(adapter); 
4.  
5. IntrospectionUtils.setProperty(protocolHandler, "jkHome", System.getProperty("catalina.base")); 
6.  
7. try { 
8.     protocolHandler.init(); 
9. } catch (Exception e) { 
10.     throw new LifecycleException(MESSAGES.protocolHandlerInitFailed(e)); 
11. } 

        // Initializa adapter        adapter = new CoyoteAdapter(this);        protocolHandler.setAdapter(adapter);        IntrospectionUtils.setProperty(protocolHandler, "jkHome", System.getProperty("catalina.base"));        try {            protocolHandler.init();        } catch (Exception e) {            throw new LifecycleException(MESSAGES.protocolHandlerInitFailed(e));        }

Http11Protocol init()

Http11Protocol 它有一个 Http11ConnectionHandler Handler，该 Handler 实现 `org.apache.tomcat.util.net.JIoEndpoint.Handler` 接口，Http11Protocol 同样有一个 JIoEndpoint 属性，该属性用来处理 incoming TCP connections，如下代码段所示：

[java] view plain copy print?

1. protected Http11ConnectionHandler cHandler =new Http11ConnectionHandler(this); 
2. protected JIoEndpoint endpoint = new JIoEndpoint(); 

    protected Http11ConnectionHandler cHandler = new Http11ConnectionHandler(this);    protected JIoEndpoint endpoint = new JIoEndpoint();

Http11Protocol 初始化主要包括：

• 给 JIoEndpoint 设定名字，默认设定的名字为 http-/127.0.0.1:8080
• 给 JIoEndpoint 设定 socket handler，设定的 handler 为 Http11ConnectionHandler，该 handler 的作用是 Handling of accepted sockets
  
• 调运 JIoEndpoint 的初始化方法
  

JIoEndpoint init()

JIoEndpoint，关于此类的作用之前我们有说，对该类最直接的总结如下：

[java] view plain copy print?

1. /**
2. * Handle incoming TCP connections.
3. *
4. * This class implement a simple server model: one listener thread accepts on a socket and
5. * creates a new worker thread for each incoming connection.
6. *
7. * More advanced Endpoints will reuse the threads, use queues, etc.
8. *
9. * @author James Duncan Davidson
10. * @author Jason Hunter
11. * @author James Todd
12. * @author Costin Manolache
13. * @author Gal Shachor
14. * @author Yoav Shapira
15. * @author Remy Maucherat
16. */ 
17. public class JIoEndpoint { 

/** * Handle incoming TCP connections. * * This class implement a simple server model: one listener thread accepts on a socket and * creates a new worker thread for each incoming connection. * * More advanced Endpoints will reuse the threads, use queues, etc. * * @author James Duncan Davidson * @author Jason Hunter * @author James Todd * @author Costin Manolache * @author Gal Shachor * @author Yoav Shapira * @author Remy Maucherat */public class JIoEndpoint {

JIoEndpoint 初始化包括：

• 初始化 Acceptor thread count，默认初始设定的 Acceptor thread count 为 1
• 初始化 ServerSocketFactory，并通过初始化的 ServerSocketFactory 创建 ServerSocket
  

Connector start()

Connector 开始方法验证更新当前的状态，并调运 Http11Protocol 的开始方法

Http11Protocol start()

Http11Protocol 的开始方法中直接调运 JIoEndpoint 的开始方法。

JIoEndpoint start()

JIoEndpoint 的开始方法主要包括：

如果外部基于 Executor 的线程池为空，则初始化内部的 workers 栈，该栈保存Worker，初始化的栈大小定义如下：

[java] view plain copy print?

1. protected int maxThreads = (org.apache.tomcat.util.Constants.LOW_MEMORY) ?64 : ((Constants.MAX_THREADS == -1) ?512 * Runtime.getRuntime().availableProcessors() : Constants.MAX_THREADS); 

 protected int maxThreads = (org.apache.tomcat.util.Constants.LOW_MEMORY) ? 64 : ((Constants.MAX_THREADS == -1) ? 512 * Runtime.getRuntime().availableProcessors() : Constants.MAX_THREADS);

如上：

• 如果通过系统参数 -Dorg.apache.tomcat.util.LOW_MEMORY=true，则初始化的栈大小为 64
• 如果通过系统参数 -Dorg.apache.tomcat.util.net.MAX_THREADS=XXX 指定最大值，则初始化的栈大小为系统参数指定的最大值
  
• 如果没有通过系统参数指定 MAX_THREADS，则初始化的栈大小为Runtime.getRuntime().availableProcessors()
  

启动 Poller 线程，默认线程的名字为 http-/127.0.0.1:8080-Poller。

启动 Acceptor 线程，默认线程的名字为 http-/127.0.0.1:8080-Acceptor-0

如下代码段显示如上逻辑

[java] view plain copy print?

1. public void start() 
2.         throws Exception { 
3.         // Initialize socket if not done before 
4.         if (!initialized) { 
5.             init(); 
6.         } 
7.         if (!running) { 
8.             running = true; 
9.             paused = false; 
10.  
11.             // Create worker collection 
12.             if (executor == null) { 
13.                 workers = new WorkerStack(maxThreads); 
14.             } 
15.  
16.             // Start event poller thread 
17.             eventPoller = new Poller(); 
18.             eventPoller.init(); 
19.             Thread pollerThread = new Thread(eventPoller, getName() +"-Poller"); 
20.             pollerThread.setPriority(threadPriority); 
21.             pollerThread.setDaemon(true); 
22.             pollerThread.start(); 
23.  
24.             // Start acceptor threads 
25.             for (int i =0; i < acceptorThreadCount; i++) { 
26.                 Thread acceptorThread = new Thread(new Acceptor(), getName() +"-Acceptor-" + i); 
27.                 acceptorThread.setPriority(threadPriority); 
28.                 acceptorThread.setDaemon(daemon); 
29.                 acceptorThread.start(); 
30.             } 
31.         } 
32.     } 

public void start()        throws Exception {        // Initialize socket if not done before        if (!initialized) {            init();        }        if (!running) {            running = true;            paused = false;            // Create worker collection            if (executor == null) {                workers = new WorkerStack(maxThreads);            }            // Start event poller thread            eventPoller = new Poller();            eventPoller.init();            Thread pollerThread = new Thread(eventPoller, getName() + "-Poller");            pollerThread.setPriority(threadPriority);            pollerThread.setDaemon(true);            pollerThread.start();            // Start acceptor threads            for (int i = 0; i < acceptorThreadCount; i++) {                Thread acceptorThread = new Thread(new Acceptor(), getName() + "-Acceptor-" + i);                acceptorThread.setPriority(threadPriority);                acceptorThread.setDaemon(daemon);                acceptorThread.start();            }        }    }

如何理解 max-connections

JBoss Web 中关于max-connections 的定义如下

[html] view plain copy print?

1. <subsystemxmlns="urn:jboss:domain:web:1.4"default-virtual-server="default-host"native="false"> 
2.             <connectorname="http"protocol="HTTP/1.1"scheme="http"socket-binding="http"max-connections="200"/> 

<subsystem xmlns="urn:jboss:domain:web:1.4" default-virtual-server="default-host" native="false">            <connector name="http" protocol="HTTP/1.1" scheme="http" socket-binding="http" max-connections="200" />

如上，如果我们定义了 max-connections，WebConnectorService 开始方法中会有如下逻辑：

• 设定 JIoEndpoint 中 pollerSize，如下代码:

[java] view plain copy print?

1. protected int pollerSize = (org.apache.tomcat.util.Constants.LOW_MEMORY) ?128 : (32 *1024); 
2. public void setPollerSize(int pollerSize) {this.pollerSize = pollerSize; } 
3. public int getPollerSize() {return pollerSize; } 

    protected int pollerSize = (org.apache.tomcat.util.Constants.LOW_MEMORY) ? 128 : (32 * 1024);    public void setPollerSize(int pollerSize) { this.pollerSize = pollerSize; }    public int getPollerSize() { return pollerSize; }

如上，默认的 pollerSize 如果没有 -Dorg.apache.tomcat.util.LOW_MEMORY=true 设定，它的值为 32 * 1024。

• 设定 JIoEndpoint 中 maxThreads，如下代码段：

[java] view plain copy print?

1. protected int maxThreads = (org.apache.tomcat.util.Constants.LOW_MEMORY) ?64 : ((Constants.MAX_THREADS == -1) ?512 * Runtime.getRuntime().availableProcessors() : Constants.MAX_THREADS); 
2. public void setMaxThreads(int maxThreads) {this.maxThreads = maxThreads; } 
3. public int getMaxThreads() {return maxThreads; } 

    protected int maxThreads = (org.apache.tomcat.util.Constants.LOW_MEMORY) ? 64 : ((Constants.MAX_THREADS == -1) ? 512 * Runtime.getRuntime().availableProcessors() : Constants.MAX_THREADS);    public void setMaxThreads(int maxThreads) { this.maxThreads = maxThreads; }    public int getMaxThreads() { return maxThreads; }

注意，该 maxThreads 用来初始化内部的 workers 栈的大小。

JIoEndpoint 处理 Socket 请求

JIoEndpoint 处理 Socket 请求如下图所示

如上，首先 Acceptor 线程（通常名字为 http-/127.0.0.1:8080-Acceptor-0）阻塞等待 Socket 连接，如下所示：

[java] view plain copy print?

1. "http-/127.0.0.1:8080-Acceptor-0" daemon prio=10 tid=0x49ed5800 nid=0xbe9 runnable [0x49789000] 
2.    java.lang.Thread.State: RUNNABLE 
3.         at java.net.PlainSocketImpl.socketAccept(Native Method) 
4.         at java.net.AbstractPlainSocketImpl.accept(AbstractPlainSocketImpl.java:398) 
5.         at java.net.ServerSocket.implAccept(ServerSocket.java:522) 
6.         at java.net.ServerSocket.accept(ServerSocket.java:490) 
7.         at org.apache.tomcat.util.net.DefaultServerSocketFactory.acceptSocket(DefaultServerSocketFactory.java:61) 
8.         at org.apache.tomcat.util.net.JIoEndpoint$Acceptor.run(JIoEndpoint.java:309) 
9.         at java.lang.Thread.run(Thread.java:722) 
10.  
11.    Locked ownable synchronizers: 
12.         - None