新启动的JVM的方法级别分析

Question

In my application, a new JVM is launched when ever a new resource is created. I am able to profile the newly launched JVM by connecting it in yourkit.

Right now I am able to connect to JVM only after it is ready and after that I am able to profile it but i want to profile the JVM methods while is is coming up ie profile the methods calls of the JVM while it is initializing.

Is there any way i can achieve this?

Reason for this is, some methods which are only invoked during initialization are causing some problem and those can't be profiled once the JVM is created and is ready.

Thanks

Answer 1

If under "JVM methdos" you mean Java method which are being called on JVM initialization, then you are able to do it with yourkit. You have to:

• Run JVM with YourKit agent just from start http://www.yourkit.com/docs/java/help/agent.jsp

• Start CPU profiling ("tracing" and "sampling" options) just from start http://www.yourkit.com/docs/java/help/startup_options.jsp

After that you should see "early" call in YourKit UI after connection.

Answer 2

You want to do a remote debugging session on code that runs in the initial few seconds of your app being launched.

A problem that you can run into when attempting to do this is that since the code runs right in the beginning, the JVM may rush past it before you have had a chance to attach a debugger via Eclipse and set your break points.

The solution is to setup your JVM/debugging config so that it is set to suspend at startup.

A typical way to setup remote debugging is to use the following JVM argument in the code used to launch your application so that a debugger can later attach itself to port 8000.

-Xrunjdwp:transport=dt_socket,server=y,suspend=n,address=8000

Infact this is what Eclipse does when you launch an app in debug mode rather than normal mode. It adds this line in the JVM arguments used when launching your application.

Note the suspend=n. If that is set to y, the JVM will suspend on startup. It will wait for a debugger to attach to it and release it before it will proceed.

So using the suspend flag, our problem is solved.

Source: http://www.onkarjoshi.com/blog/224/how-to-suspend-vm-on-startup-when-remote-debugging-your-java-app/