Thank you for response, Kris!
The only goal I'm trying to achieve is to to compute sizes of classes
loaded in perm gen.
As I've understood, this is possible only by using Serviceability Agent?
- Sergei
On 20.03.2014 00:12, Krystal Mok wrote:
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 <[email protected]
<mailto:[email protected]>> 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" <[email protected]
<mailto:[email protected]>>:
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 <[email protected]
<mailto:[email protected]>> 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
