Hi Sergei, "jmap -permstat", or "PermStat" itself is an utility based on the Serviceability Agent.
For your reference, I've written other utilities based on SA, some of them listed here: http://rednaxelafx.iteye.com/blog/1814429 The easiest way to write your own custom SA-based tool is to inherit from the sun.jvm.hotspot.tools.Tool class and implement your logic in a "public void run()" method. Do please keep in mind that SA is a out-of-process debugger, and it works very differently from Java agents or JVMTI agents, in that the latter two runs in-process. A question to you is: what are you really trying to achieve? Whether or not using SA is applicable for you very much depends on what you're trying to do. I don't know of any JVMTI functions that could give you information on the InstanceKlass. The heap iterations functions don't expose information on VM metadata, as can be seen here: http://hg.openjdk.java.net/jdk7u/jdk7u/hotspot/file/tip/src/share/vm/services/serviceUtil.hpp#l38 (In JDK 8, there is no PermGen, and the VM metadata is moved out to Metaspace which is in native memory, and JVMTI IterateThroughHeap() doesn't even iterate over that space.) - Kris On Wed, Mar 19, 2014 at 1:22 PM, Sergei Mihhailov <rs...@yandex.com> wrote: > Thank you for response, Kris! > > I'm writing both "Java agent" and JVMTI agent. > > Are you suggesting that I should write Serviceability Agent instead? If > yes, then could you please pinpoint me into the right direction? Because it > wasn't clear to me how can I write my own custom Serviceability Agent. > > By the way, is it possible to compute sizes of classes loaded in perm gen > only by using "Java Agent" and JVMTI agent? > > - Sergei > > 19.03.2014, 17:39, "Krystal Mok" <rednaxel...@gmail.com>: > > Hi Sergei, > > Are you using PermStat in the context of Serviceability Agent? In other > words, is the agent you're writing a "Serviceability Agent", or something > else, like a "Java agent" as in java.lang.instrument, or a "JVMTI agent"? > SA uses different means to connect to the target VM from the other types of > agents, so you can't mix them up. > > - Kris > > On Wednesday, March 19, 2014, Sergei Mihhailov <rs...@yandex.ru> wrote: > > Greetings, > > I'm writing special purpose java agent to compute sizes of classes loaded > in perm gen. Basically reimplementing some functionality of "jmap > -permstat". But in order to do that, I need to get instances of > InstanceKlass for all loaded classes. > > I've looked up PermStat source code, and tried to use it internally in my > agent using its start() method. This attempt failed : > "sun.jvm.hotspot.debugger.DebuggerException: Can't attach to the process" > > Is it somehow possible to compute sizes of classes loaded in perm gen? > > > Thanks, > Sergei > >
