Tuesday, February 17, 2009

Say goodbye to awful concurrency bugs -- Showcase of MTRAT on Tomcat

Multicore hardware trend drives more and more program archtects and progreammers take the double-edged sward -- parallel program, even it has been very notorious for its non-determined bugs, such race condition and deadlock, however mostly their injuries were beaten black and blue by this double-edged sward. What should and could we do? MTRAT might be one of the live-saving straw.

Today, I will show how do we use MTRAT to find concurrency defects in Tomcat, and hope this tool and article could comfort ones heart if he/she has been hurt by concurrency bugs a lot.

In one word, MTRAT instrument java classes when they are loaded by JVM, and runtime analysis engine is running during the program's execution. Once it finds some potential problems, it will report them with sufficient information, such as thread backtrace, class name, object id, etc.

Now, let us start the journey of MTRAT on Tomcat (my operating system is Linux, so this showcase is done under Linux),

  1. Download MTRAT from its webiste http://www.alphaworks.ibm.com/tech/mtrat, and configure it following the user manual.
  2. Start tomcat.
    [qiyao@mtrat-test:~/SourceCode/apache-tomcat-6.0.16]$ ./bin/startup.sh
  3. check java process of tomcat, record the process information of tomcat java process.
    [qiyao@mtrat-test:~/SourceCode/apache-tomcat-6.0.16]$ ps -elf | grep tomcat
    0 S qiyao 7415 1 4 81 0 - 143807 stext 11:13 pts/1 00:00:10 /opt/ibm-java-i386-60/bin/java -Djava.util.logging.manager=org.apache.juli.ClassLoaderLogManager -Djava.util.logging.config.file=/home/qiyao/SourceCode/apache-tomcat-6.0.16/conf/logging.properties -Djava.endorsed.dirs=/home/qiyao/SourceCode/apache-tomcat-6.0.16/endorsed -classpath :/home/qiyao/SourceCode/apache-tomcat-6.0.16/bin/bootstrap.jar -Dcatalina.base=/home/qiyao/SourceCode/apache-tomcat-6.0.16 -Dcatalina.home=/home/qiyao/SourceCode/apache-tomcat-6.0.16 -Djava.io.tmpdir=/home/qiyao/SourceCode/apache-tomcat-6.0.16/temp org.apache.catalina.startup.Bootstrap start

  4. stop tomcat,
    [qiyao@mtrat-test:~/SourceCode/apache-tomcat-6.0.16]$ ./bin/shutdown.sh

  5. Replace java with mtrat in process command line, and run it,
    ~/MTRAT/mtrat/mtrat -x java.*:com.*:sun.*:org.apache.xerces.*:javax.managment.* -Djava.util.logging.manager=org.apache.juli.ClassLoaderLogManager -Djava.util.logging.config.file=/home/qiyao/SourceCode/apache-tomcat-6.0.16/conf/logging.properties -Djava.endorsed.dirs=/home/qiyao/SourceCode/apache-tomcat-6.0.16/endorsed -classpath :/home/qiyao/SourceCode/apache-tomcat-6.0.16/bin/bootstrap.jar -Dcatalina.base=/home/qiyao/SourceCode/apache-tomcat-6.0.16 -Dcatalina.home=/home/qiyao/SourceCode/apache-tomcat-6.0.16 -Djava.io.tmpdir=/home/qiyao/SourceCode/apache-tomcat-6.0.16/temp org.apache.catalina.startup.Bootstrap start
  6. Access tomcat via browser and click examples shipped in tomcat, then you will see some data races are report in console,
Actually, user could deploy some applications to tomcat, and drive http requests to tomcat. Then, MTRAT could find more potential race conditions. In our experiments, we find some potential race conditions in tomcat 6.0.16, and one of them has been confirmed by tomcat commnity. See bug 45608

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