Oop.iterateFields() should support CompressedKlassPointers again (original) (raw)

云达(Yunda) yunda.mly at taobao.com
Mon Feb 25 17:14:55 PST 2013

Kris,

Thanks a lot!

Regards, Yunda

From: serviceability-dev-bounces at openjdk.java.net [mailto:serviceability-dev-bounces at openjdk.java.net] On Behalf Of Krystal Mo Sent: Monday, February 25, 2013 7:19 PM To: serviceability-dev at openjdk.java.net Subject: Re: Oop.iterateFields() should support CompressedKlassPointers again

Hi Yunda,

Thanks for fixing this. I actually have the exact same fix for this problem, along with fixes for some other problems in SA in my local workspace, but haven't come around to sending it out for public review yet.

I think this is just a missed change in JDK-7054512. I have created a JIRA issue for you: JDK-8008796: SA: Oop.iterateFields() should support CompressedKlassPointers again. I'll prepare a webrev and send it out for official review later.

Thanks, Kris

On 2013/2/25 2:58, 云达(Yunda) wrote: Hi all,

When I used CLHSDB just now I met this error: hsdb> inspect 0x00000000ee255080 instance of "java/io/InputStream" @ 0x00000000ee255080 @ 0x00000000ee255080 (size = 24) Exception in thread "main" java.lang.InternalError: unimplemented at sun.jvm.hotspot.oops.Oop.iterateFields(Oop.java:151) at sun.jvm.hotspot.oops.Instance.iterateFields(Instance.java:66) at sun.jvm.hotspot.oops.Oop.iterate(Oop.java:143) at sun.jvm.hotspot.ui.tree.OopTreeNodeAdapter.getChildCount(OopTreeNodeAdapter.java:65) at sun.jvm.hotspot.CommandProcessor$Command.printNode(CommandProcessor.java:231) at sun.jvm.hotspot.CommandProcessor$24.doit(CommandProcessor.java:1008) at sun.jvm.hotspot.CommandProcessor.executeCommand(CommandProcessor.java:1897) at sun.jvm.hotspot.CommandProcessor.executeCommand(CommandProcessor.java:1867) at sun.jvm.hotspot.CommandProcessor.run(CommandProcessor.java:1747) at sun.jvm.hotspot.CLHSDB.run(CLHSDB.java:91) at sun.jvm.hotspot.CLHSDB.main(CLHSDB.java:35)

I found it’s caused by the code of sun.jvm.hotspot.oops.Oop.iterateFields(): void iterateFields(OopVisitor visitor, boolean doVMFields) { if (doVMFields) { visitor.doCInt(mark, true); if (VM.getVM().isCompressedKlassPointersEnabled()) { throw new InternalError("unimplemented"); } else { visitor.doMetadata(klass, true); } } }

When compressed oops( which is by default) are used an InternalError of “unimplemented” will be throwed. But actually it can be implemented easily by just one line of code: visitor.doMetadata(compressedKlass, true);

I checked the hotspot-rt repo and I found it was implemented this way before changeset 3601, the main implementation of NPG. Since 3601 changed a whole lot of stuff, the ‘compressedKlass’ field couldn’t get the right value, as in line 51: // compressedKlass = new CIntField(type.getCIntegerField("_metadata._compressed_klass"), 0); So the code in iterateFields() was changed to throwing an InternalError accordingly.

But the ‘compressedKlass’ field can get the right value now. So I think it’s time to change the code back and here’s the diff against the latest hotspot-rt: diff -r 2f881161d085 agent/src/share/classes/sun/jvm/hotspot/oops/Oop.java --- a/agent/src/share/classes/sun/jvm/hotspot/oops/Oop.java Mon Feb 25 18:25:24 2013 +0800 +++ b/agent/src/share/classes/sun/jvm/hotspot/oops/Oop.java Mon Feb 25 18:47:08 2013 +0800 @@ -148,7 +148,7 @@ if (doVMFields) { visitor.doCInt(mark, true); if (VM.getVM().isCompressedKlassPointersEnabled()) {

Regards, Yunda

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