Getting a thread dump from Tomcat running as a Windows service
by Albert MacSweenyWe’re supporting a java application deployed on Tomcat, which is running as a windows service. On Friday the logs showed that parts of the application were frequently timing out while trying to aquire a DB connection from a pool. We wanted to get a thread dump to see if any threads holding connections were deadlocked. If Tomcat had been started from a console this would be straightforward, unfortunately it wasn’t, and we didn’t have the option to re-start it on the production server.
One useful tool is the free web start version of stack trace. We had no joy with this either though. Our remote desktop session was not the account from which the service was started. Stack trace helpfully suggests using Start->run->”mstsc /console” to start the remote desktop session in this case, but this would have terminated other sessions that were open to the server, and therefore wasn’t an option for us.
Cue a moment of inspiration from Rob, which resulted in a simple jsp that will output a thread dump. Note that your applicaiton must be running on at least java 5.0 for this to work. Just make a simple jsp with the following snippit as the body of the page, and drop it in the web root of your application. Then fire up a browser, navigate to the jsp and view the dump without even having to restart Tomcat!
<body>
<center><h1>Thread Dump</h1></center>
<pre>
<%
StringBuffer sb = new StringBuffer();
Map st = Thread.getAllStackTraces();
for (Map.Entry e : st.entrySet() ) {
StackTraceElement[] el = e.getValue();
Thread t= e.getKey();
sb.append(”\”" ).append( t.getName() ).append( “\” ” );
sb.append( t.isDaemon()?”daemon”:”" ).append( ” prio=” ).append( t.getPriority() );
sb.append ( ” Thread id=” ).append( t.getId() ).append( ” ” ).append( t.getState() );
sb.append( “\n” );
for (StackTraceElement line: el) {
sb.append(”\t”+line + “\n”);
}
sb.append(”\n”);
}
% >
<%=sb.toString() %>
</pre>
</body>