Tomcat - Tomcat 网络通信模型剖析 & 并发参数解读

秒速五厘米 2023-02-14 15:34 8阅读 0赞

### 文章目录 ###

*  什么是IO
 *  Tomcat 支持四种线程模型
 *  Tomcat 如何使用指定IO模型
 *  Tomcat BIO VS NIO
 *   *  BIO
     *  NIO
 *  影响 BIO/NIO线程数量的多少的因素
 *  Tomcat connector 并发参数解读

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--------------------

# 什么是IO #

IO是指为数据传输所提供的输入输出流，其输入输出对象可以是：文件、网络服务、内存等。

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3lhbmdzaGFuZ3dlaQ_size_16_color_FFFFFF_t_70 1]

举个例子，假设应用在从硬盘中读取一个大文件过程中， CPU会与硬盘一样出于高负荷状态么？

CPU 没有太高的增涨 。 通常情况下IO操作是比较耗时的，所以为了高效的使用硬件，应用程序可以用一个专门线程进行IO操作，而另外一个线程则利用CPU的空闲去做其它计算。这种为提高应用执行效率而采用的IO操作方法即为IO模型。

--------------------

# Tomcat 支持四种线程模型 #

<table> 
 <thead> 
  <tr> 
   <th>IO模型</th> 
   <th>描述</th> 
  </tr> 
 </thead> 
 <tbody> 
  <tr> 
   <td>BIO</td> 
   <td>同步阻塞式IO，即Tomcat使用传统的java.io进行操作。该模式下每个请求都会创建一个线程，对性能开销大，不适合高并发场景。优点是稳定，适合连接数目小且固定架构。</td> 
  </tr> 
  <tr> 
   <td>NIO</td> 
   <td>同步非阻塞式IO，jdk1.4 之后实现的新IO。该模式基于多路复用选择器监测连接状态在同步通知线程处理，从而达到非阻塞的目的。比传统BIO能更好的支持并发性能。Tomcat 8.0之后默认采用该模式</td> 
  </tr> 
  <tr> 
   <td>APR</td> 
   <td>全称是 Apache Portable Runtime/Apache可移植运行库)，是Apache HTTP服务器的支持库。可以简单地理解为，Tomcat将以JNI的形式调用Apache HTTP服务器的核心动态链接库来处理文件读取或网络传输操作。使用需要编译安装APR 库</td> 
  </tr> 
  <tr> 
   <td>AIO (asynchronous I/O)</td> 
   <td>异步非阻塞式IO，jdk1.7后之支持 。与nio不同在于不需要多路复用选择器，而是请求处理线程执行完程进行回调调知，已继续执行后续操作。Tomcat 8之后支持。</td> 
  </tr> 
 </tbody> 
</table>

--------------------

# Tomcat 如何使用指定IO模型 #

配置 server.xml 文件当中的 `<Connector protocol="HTTP/1.1">` 修改即可。

默认配置 8.0 protocol=“HTTP/1.1” 8.0 之前是 BIO 8.0 之后是NIO

BIO: `protocol ="org.apache.coyote.http11.Http11Protocol"`

NIO: `protocol ="org.apache.coyote.http11.Http11NioProtocol"`

AIO: `protocol ="org.apache.coyote.http11.Http11Nio2Protocol"`

APR: `protocol ="org.apache.coyote.http11.Http11AprProtocol"`

tomcat 8 以前 默认的是 BIO ， 8 默认是 NIO

--------------------

# Tomcat BIO VS NIO #

在高并发场景下BIO与NIO的线程数的变化

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3lhbmdzaGFuZ3dlaQ_size_16_color_FFFFFF_t_70 2]

生产环境上，模拟了处理较慢的过程。

为什么差异这么大呢？

我们先看下这两种模型的区别

## BIO ##

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3lhbmdzaGFuZ3dlaQ_size_16_color_FFFFFF_t_70 3]

源码翻一翻

我们下个Tomcat 7的版本

[https://archive.apache.org/dist/tomcat/tomcat-7/v7.0.99/src/][https_archive.apache.org_dist_tomcat_tomcat-7_v7.0.99_src]

7嘛 ，默认的BIO， 对应的class `org.apache.coyote.http11.Http11Protocol.java`

看下 Http11Protocol构造函数

public Http11Protocol() { 
            endpoint = new JIoEndpoint();
            cHandler = new Http11ConnectionHandler(this);
            ((JIoEndpoint) endpoint).setHandler(cHandler);
            setSoLinger(Constants.DEFAULT_CONNECTION_LINGER);
            setSoTimeout(Constants.DEFAULT_CONNECTION_TIMEOUT);
            setTcpNoDelay(Constants.DEFAULT_TCP_NO_DELAY);
        }

重点 JIoEndpoint ------> Java I/O Endpoint

![在这里插入图片描述][20200603214208257.png]

对应JIoEndpoint 中的

![在这里插入图片描述][20200603214237851.png]

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熟悉吧 Socket， 同步阻塞。

继续  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3lhbmdzaGFuZ3dlaQ_size_16_color_FFFFFF_t_70 7]

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这个getExecutor（）获取的 就是 那个线程池，用来处理任务的

怎么处理的呢？ 继续

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3lhbmdzaGFuZ3dlaQ_size_16_color_FFFFFF_t_70 9]

--------------------

## NIO ##

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3lhbmdzaGFuZ3dlaQ_size_16_color_FFFFFF_t_70 10]

老套路

下载 apache-tomcat-8.5.55-src

Http11NioProtocol的构造函数  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3lhbmdzaGFuZ3dlaQ_size_16_color_FFFFFF_t_70 11]

重点 NioEndpoint

![在这里插入图片描述][20200603222242401.png]

Acceptor 和 SocketProcessor 大致形同， 主要在于Poller .

先看看Acceptor ，和BIO一样 ，有点不一样的是，Acceptor 交个 Poller处理

![在这里插入图片描述][20200603222807336.png]  
进入

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3lhbmdzaGFuZ3dlaQ_size_16_color_FFFFFF_t_70 12]  
添加事件  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3lhbmdzaGFuZ3dlaQ_size_16_color_FFFFFF_t_70 13]

public class Poller implements Runnable {  
     
    
    }

那就看run方法

public void run() { 
                // Loop until destroy() is called 轮询
                while (true) { 
    
                    boolean hasEvents = false;
    
                    try { 
                        if (!close) { 
                            hasEvents = events();
                            // > 0 说明有socket需要处理
                            if (wakeupCounter.getAndSet(-1) > 0) { 
                                //if we are here, means we have other stuff to do
                                //do a non blocking select
                                keyCount = selector.selectNow();
                            } else { 
                                keyCount = selector.select(selectorTimeout);
                            }
                            wakeupCounter.set(0);
                        }
                        if (close) { 
                            events();
                            timeout(0, false);
                            try { 
                                selector.close();
                            } catch (IOException ioe) { 
                                log.error(sm.getString("endpoint.nio.selectorCloseFail"), ioe);
                            }
                            break;
                        }
                    } catch (Throwable x) { 
                        ExceptionUtils.handleThrowable(x);
                        log.error("",x);
                        continue;
                    }
                    //either we timed out or we woke up, process events first
                    if ( keyCount == 0 ) hasEvents = (hasEvents | events());
    
                    Iterator<SelectionKey> iterator =
                        keyCount > 0 ? selector.selectedKeys().iterator() : null;
                    // Walk through the collection of ready keys and dispatch
                    // any active event.
                    while (iterator != null && iterator.hasNext()) { 
                        SelectionKey sk = iterator.next();
                        NioSocketWrapper attachment = (NioSocketWrapper)sk.attachment();
                        // Attachment may be null if another thread has called
                        // cancelledKey()
                        if (attachment == null) { 
                            iterator.remove();
                        } else { 
                            iterator.remove();
                            processKey(sk, attachment);
                        }
                    }//while
    
                    //process timeouts
                    timeout(keyCount,hasEvents);
                }//while
    
                getStopLatch().countDown();
            }

--------------------

# 影响 BIO/NIO线程数量的多少的因素 #

BIO

*  线程数量 会受到 客户端阻塞、网络延迟、业务处理慢===>线程数会更多

NIO

*  线程数量 会受到业务处理慢===>线程数会更多

--------------------

# Tomcat connector 并发参数解读 #

<table> 
 <thead> 
  <tr> 
   <th>名称</th> 
   <th>描述</th> 
  </tr> 
 </thead> 
 <tbody> 
  <tr> 
   <td>acceptCount</td> 
   <td>等待最大队列</td> 
  </tr> 
  <tr> 
   <td>address</td> 
   <td>绑定客户端特定地址，127.0.0.1</td> 
  </tr> 
  <tr> 
   <td>bufferSize</td> 
   <td>每个请求的缓冲区大小。bufferSize * maxThreads</td> 
  </tr> 
  <tr> 
   <td>compression</td> 
   <td>是否启用文档压缩</td> 
  </tr> 
  <tr> 
   <td>compressableMimeTypes</td> 
   <td>text/html,text/xml,text/plain</td> 
  </tr> 
  <tr> 
   <td>connectionTimeout</td> 
   <td>客户发起链接 到 服务端接收为止，中间最大的等待时间</td> 
  </tr> 
  <tr> 
   <td>connectionUploadTimeout</td> 
   <td>upload 情况下连接超时时间</td> 
  </tr> 
  <tr> 
   <td>disableUploadTimeout</td> 
   <td>true 则使用connectionTimeout</td> 
  </tr> 
  <tr> 
   <td>enableLookups</td> 
   <td>禁用DNS查询 true</td> 
  </tr> 
  <tr> 
   <td>keepAliveTimeout</td> 
   <td>当长链接闲置 指定时间主动关闭 链接 ，前提是客户端请求头 带上这个 head"connection" " keep-alive"</td> 
  </tr> 
  <tr> 
   <td>maxKeepAliveRequests</td> 
   <td>最大的 长连接数</td> 
  </tr> 
  <tr> 
   <td>maxHttpHeaderSize</td> 
   <td>HTTP请求、响应头信息的最大大小，默认是8192bytes</td> 
  </tr> 
  <tr> 
   <td>maxSpareThreads</td> 
   <td>BIO 模式下 最多线闲置线程数</td> 
  </tr> 
  <tr> 
   <td>maxThreads</td> 
   <td>（执行线程） 最大执行线程数</td> 
  </tr> 
  <tr> 
   <td>minSpareThreads</td> 
   <td>(初始线业务线程 10) BIO 模式下 最小线闲置线程数</td> 
  </tr> 
 </tbody> 
</table>

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[https_archive.apache.org_dist_tomcat_tomcat-7_v7.0.99_src]: https://archive.apache.org/dist/tomcat/tomcat-7/v7.0.99/src/
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