Request for Review: JDK-8008796: SA: Oop.iterateFields() should support CompressedKlassPointers again

Fri Mar 15 11:13:19 PDT 2013

Looks good.
Coleen

On 3/15/2013 1:55 PM, Krystal Mo wrote:
> cc'ing hotspot-runtime for a review
>
>
> -------- Original Message --------
> Subject: 	Request for Review: JDK-8008796: SA: Oop.iterateFields() 
> should support CompressedKlassPointers again
> Date: 	Mon, 25 Feb 2013 18:03:20 -0800
> From: 	Krystal Mo <krystal.mo at oracle.com>
> Organization: 	Oracle Corporation
> To: 	"云达(Yunda)" <yunda.mly at taobao.com>
> CC: 	serviceability-dev at openjdk.java.net 
> <serviceability-dev at openjdk.java.net>
>
>
>
> Hi all,
>
> Could I have a review for this small change, please?
>
> Webrev: http://cr.openjdk.java.net/~kmo/8008796/webrev.00/
> CR: http://bugs.sun.com/view_bug.do?bug_id=8008796 (should be 
> available externally soon)
>
> 8008796: SA: Oop.iterateFields() should support 
> CompressedKlassPointers again
> Summary: add a missing change from JDK-7054512 so that 
> Oop.iterateFields() works with UseCompressedKlassPointers
> Reviewed-by: ?
> Contributed-by: yunda.mly at taobao.com
>
> Thanks,
> Kris
>
> On 2013/2/25 17:14, 云达(Yunda) wrote:
>>
>> 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()) {
>>
>>     -        throw new InternalError("unimplemented");
>>
>>     + visitor.doMetadata(compressedKlass, true);
>>
>>            } else {
>>
>>     visitor.doMetadata(klass, true);
>>
>>            }
>>
>>     Regards,
>>
>>     Yunda
>>
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>>
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