Since a servlet is blocking, a normal HTTP communication makes the thread wait. So there is a possibility that all the threads in the pool can be used up. By using the asynchronous http client framework Asynchronous HTTP Client framework (AHC javadocs), the thread can be released back into the pool and be made available for other purposes until the answer comes back. When the answer comes back, a callback is fired which then relays the response back to the client.

The async http client is to be used in conjunction with web containers that are configured for non blocking communication. CometProcesor with Tomcat and Continuation with Jetty are some good examples. This example uses Tomcat.

This document is organized in the following sections:

Table of Contents

About this example

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The http-local-app

The AsyncServlet in this app implements app uses the AHC and implements the CometProcessor interface. This will The CometProcessor will make it's event method invoked rather than the usual service method, according to the event which occurred. The event object gives access to the usual request and response objects, which may be used in the usual way. More information about this can be read here.

...

Stop the server.
edit geronimo_home/var/config/config.xml
add load="false" to the TomcatWebConnector gbean. The line would now look like this code
<gbean load="false" name="TomcatWebConnector">

for the module org.apache.geronimo.configs/tomcat6/<version>/car, add the following gbean

Code Block

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	XML
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<gbean gbeanInfo="org.apache.geronimo.tomcat.connector.Http11NIOConnectorGBean"
       name="org.apache.geronimo.configs/tomcat6/2.0.1/car?ServiceModule=org.apache.geronimo.configs/tomcat6/2.0.1/car,j2eeType=GBean,name=TomcatNIOConnector">
<attribute name="useExecutor">true</attribute>
<attribute name="maxThreads">40</attribute>
<attribute name="pollerThreadCount">1</attribute>
<attribute name="socket_soTimeout">5000</attribute>
<attribute name="selectorTimeout">1000</attribute>
<attribute name="connectionTimeout">60000</attribute>
<attribute name="socket_soLingerOn">true</attribute>
<attribute name="acceptorThreadCount">1</attribute>
<attribute name="port">8080</attribute>
<attribute name="pollerThreadPriority">5</attribute>
<attribute name="compressableMimeType">text/html,text/xml,text/plain</attribute>
<attribute name="socket_performanceLatency">0</attribute>
<attribute name="useComet">true</attribute>
<attribute name="useIPVHosts">false</attribute>
<attribute name="maxHttpHeaderSize">4096</attribute>
<attribute name="restrictedUserAgents" value=""/>
<attribute name="acceptorThreadPriority">5</attribute>
<attribute name="proxyPort">0</attribute>
<attribute name="maxPostSize">2097152</attribute>
<attribute name="minSpareThreads">10</attribute>
<attribute name="socketBuffer">9000</attribute>
<attribute name="redirectPort">8443</attribute>
<attribute name="bufferSize">2048</attribute>
<attribute name="socket_soReuseAddress">false</attribute>
<attribute name="useSendfile">true</attribute>
<attribute name="threadPriority">5</attribute>
<attribute name="socket_tcpNoDelay">false</attribute>
<attribute name="useBodyEncodingForURI">false</attribute>
<attribute name="maxSpareThreads">100</attribute>
<attribute name="enableLookups">true</attribute>
<attribute name="socket_performanceConnectionTime">1</attribute>
<attribute name="socket_appWriteBufSize">8192</attribute>
<attribute name="maxKeepAliveRequests">100</attribute>
<attribute name="socket_ooBInline">true</attribute>
<attribute name="socket_keyCache">500</attribute>
<attribute name="disableUploadTimeout">true</attribute>
<attribute name="socket_bufferPoolSize">104857600</attribute>
<attribute name="keepAliveTimeout">60000</attribute>
<attribute name="acceptCount">100</attribute>
<attribute name="socket_txBufSize">43800</attribute>
<attribute name="connectionLinger">-1</attribute>
<attribute name="command_line_options">true</attribute>
<attribute name="tcpNoDelay">true</attribute>
<attribute name="oomParachute">1048576</attribute>
<attribute name="socket_appReadBufSize">8192</attribute>
<attribute name="selectorPool_maxSpareSelectors">-1</attribute>
<attribute name="xpoweredBy">false</attribute>
<attribute name="socket_rxBufSize">25188</attribute>
<attribute name="maxSavePostSize">4096</attribute>
<attribute name="socket_soLingerTime">25</attribute>
<attribute name="compression">off</attribute>
<attribute name="host">0.0.0.0</attribute>
<attribute name="socket_eventCache">500</attribute>
<attribute name="socket_performanceBandwidth">1</attribute>
<attribute name="noCompressionUserAgents" value=""/>
<attribute name="name">TomcatNIOConnector</attribute>
<attribute name="socket_soKeepAlive">false</attribute>
<attribute name="socket_soTrafficClass">28</attribute>
<attribute name="socket_directBuffer">false</attribute>
<attribute name="selectorPool_maxSelectors">200</attribute>
<attribute name="emptySessionPath">false</attribute>
<attribute name="uriEncoding">ISO-8859-1</attribute>
<attribute name="allowTrace">false</attribute>
<attribute name="processCache">200</attribute>
<attribute name="socket_processorCache">500</attribute>
<attribute name="server" null="true"/>
<attribute name="proxyName" null="true"/>
<reference name="TomcatContainer">
<pattern>
<groupId>org.apache.geronimo.configs</groupId>
<artifactId>tomcat6</artifactId>
<version>2.0.1</version>
<type>car</type>
<name>TomcatWebContainer</name>
</pattern>
</reference>
<reference name="ServerInfo">
<pattern>
<groupId>org.apache.geronimo.configs</groupId>
<artifactId>j2ee-system</artifactId>
<version>2.0.1</version>
<type>car</type>
<name>ServerInfo</name>
</pattern>
</reference>
</gbean>

The gbean uses version 2.0.1. Replace that with the appropriate version of your server
Start the server.

...

Deploy samples\async-http\http-local-app\target\http-local-app-2.0-SNAPSHOT.war on the Geronimo server we configured earlier using either the consoleor the command line code
$geronimo_home/bin>./deploy.sh deploy _samples_\async-http\http-local-app\target\http-local-app-2.0-SNAPSHOT.war
Deploy samples\async-http directory\http-remote-app\target\http-remote-app-2.0-SNAPSHOT.war on any server on the remote machine.
Point your browser to http://localhost:8080/localApp/async. If you wish to override the remoteUrl set in the <init-param> of the web.xml, you may pass it as a request param (http://localhost:8080/localApp/async?remoteUrl=http://foo:8080)
You should see either a dummy html or one of the popular HTTP errors.

...

Download the client python script. You will need python installed on your machine to run this script. You can download Python from here.
The script takes 3 arguments - the name of the machine running http-local-app (AHC), the url of the server on the remote app and the number of threads. code
ahcrequest.py local_machine http://remote_machine:8080 200

Test Results

The following test results show a comparison between an AHC enhanced servlet and a normal blocking servlet. Each of these servlets are pounded by 16, 200 and 500 simultaneous requests. The output captured from the python script shows the response time for each request. These tests also demonstrate the significance of tuning the IP stacks. When none of the machines are tuned, the response time starts increasing as the number of threads start increasing. Executing a netstat command shows that most sockets are either in TIME_WAIT or CLOSED_WAIT state.

Threads	Blocking Servlet max response time (secs)	AHC Servlet max response time(secs) Blocking Servlet	HttpComponents max response time (secs)
16	5.252	2.081	5.252	1.974
100			2.975
200	25.935 200	7.575	25.935		3.358
400			6.694
500	39.590 500	12.917	3913.590051

Code location and References

Browse the sample code at http://svn.apache.org/viewvc/geronimo/samples/trunk/samples/async-http/

Check out code from svn using
svn co https://svn.apache.org/repos/asf/geronimo/samples/trunk/samples/async-http async-http

Browse the AHC code at http://svn.apache.org/viewvc/geronimo/sandbox/AsyncHttpClient

Check out code from svn using
svn co https://svn.apache.org/repos/asf/geronimo/sandbox/AsyncHttpClient ahc

View AHC's javadocs at AHC javadocs

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About this example

The http-local-app

Test Results

Code location and References

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Versions Compared

Old Version 25

New Version Current

Key

About this example

The http-local-app

Test Results

Code location and References