On 8/20/14 8:54 AM, Coleen Phillimore wrote:
Hi, it appears that my code is wrong and maybe the existing code is
wrong also. I have a spec question below.
On 8/19/14, 7:52 PM, serguei.spit...@oracle.com wrote:
On 8/19/14 3:53 PM, Daniel D. Daugherty wrote:
On 8/19/14 3:39 PM, Daniel D. Daugherty wrote:
On 8/15/14 2:18 PM, Coleen Phillimore wrote:
Summary: Use scratch_class to find EMCP methods for breakpoints if
the old methods are still running
See bug for more details. This fix also includes a change to
nmethod::metadata_do() to not walk the _method multiple times (the
_method is added to the metadata section of the nmethod), and an
attempt to help the sweeper clean up these scratch_class instance
classes sooner.
Tested with nsk tests, java/lang/instrument tests and jck tests
(which include some jvmti tests).
open webrev at http://cr.openjdk.java.net/~coleenp/8055008/
src/share/vm/oops/instanceKlass.hpp
line 1047 // RedefineClass support
Should be 'RedefineClasses'.
line 1049: void mark_newly_obsolete_methods(Array<Method*>*
old_methods,
int emcp_method_count);
The 'obsolete' part of the function name does not match with
the 'emcp' part of the parameter name. EMCP methods are 'old',
but not 'obsolete'.
Update: OK, I think I get it. We want to mark methods that are
newly transitioning from EMCP -> obsolete and the
emcp_method_count
parameter tells us if there is any work to do.
src/share/vm/oops/instanceKlass.cpp
line 3023: } // pvw is cleaned up
'pvw' no longer exists so comment is stale.
line 3455: // check the previous versions array
This comment should move above this line:
3453 for (; pv_node != NULL; ) {
and 'array' should change to 'list'.
Sorry for the bad placement of the original comment.
line 3463: last->link_previous_versions(pv_node);
So now we've overwritten the previous value of
last->previous_versions. How does that InstanceKlass
get freed? Maybe a short comment?
line 3484: // Mark the emcp method as obsolete if it's not
executing
I'm not sure about whether this is a good idea. When we had a
redefine make a method obsolete before, we knew that we could
make all older but previously EMCP methods obsolete because
the new method version did make them obsolete.
With this optimization, we're saying that no thread is
executing
the method so we're going to make it obsolete even if the
current
redefine did not do so. I worry about a method call that is in
the early stages of assembling the call stack being caught
calling a method that is now obsolete but not because of a
redefine made it obsolete. Just FYI, one of the tracing flags
catches unexpected calls to obsolete methods today and it does
catch the current system's legitimate race.
JVM/TI has an isMethodObsolete() API:
jvmtiError
IsMethodObsolete(jvmtiEnv* env,
jmethodID method,
jboolean* is_obsolete_ptr)
It would be possible for an agent to observe a method changing from
not obsolete to obsolete when that's not expected. I suspect that
this would be a spec violation.
I agree that this looks like a spec violation.
The emcp methods by definition are non-obsolete,
or in opposite, the obsolete methods are non-emcp:
http://docs.oracle.com/javase/8/docs/platform/jvmti/jvmti.html#obsoleteMethods
Old method versions may become obsolete, not emcp:
http://docs.oracle.com/javase/7/docs/platform/jvmti/jvmti.html#RedefineClasses
But maybe I'm missing something...
If an EMCP method is not running, should we save it on a previous
version list anyway so that we can make it obsolete if it's redefined
and made obsolete?
I hope, Dan will catch me if I'm wrong...
I think, we should not.
An EMCP method can not be made obsolete if it is not running.
BTW, I'm reviewing the webrev too, but probably it'd be better to switch
to updated webrev after it is ready.
Thanks,
Serguei
Currently we don't save previous versions of methods that are not
running. We didn't before permgen elimination either. If GC didn't
find the EMCP method, we would remove the entry.
Thanks,
Coleen
Thanks,
Serguei
Dan
line 3527: // clear out any matching EMCP method entries the
hard way.
Perhaps "mark" instead of "clear out"?
old line 3659: if (!method->is_obsolete() &&
new line 3546: if (method->is_emcp() &&
The old code is correct. The old code won't remark a method
that
was already made obsolete so there won't be more than one
trace
message for that operation.
line 3581: // stack, and set emcp methods on the stack.
In comments 'emcp' should be 'EMCP'. We did not do that in the
code because of HotSpot's variable name style.
Also, set what on EMCP methods on the stack?
line 3591: ... If emcp method from
line 3592: // a previous redefinition may be made obsolete by
this redefinition.
Having trouble parsing this comment.
src/share/vm/oops/method.hpp
line 693: // emcp methods (equivalent method except constant
pool is different)
line 694: // that are old but not obsolete or deleted.
Perhaps:
// EMCP methods are old but not obsolete or deleted.
Equivalent
// Modulo Constant Pool means the method is equivalent except
// the constant pool and instructions that access the constant
// pool might be different.
src/share/vm/prims/jvmtiImpl.cpp
No comments.
src/share/vm/prims/jvmtiRedefineClasses.cpp
No comments.
src/share/vm/code/nmethod.cpp
So in the original code f(_method) was being called two extra
times? (once in the while-loop and once at the end) So I'm
guessing that f(_method) is properly called when the rest of
the metadata is handled in the nmethod (line 2085)?
src/share/vm/memory/universe.cpp
No comments (resisting 'The Walking Dead' ref...)
test/runtime/RedefineTests/RedefineFinalizer.java
No comments.
test/runtime/RedefineTests/RedefineRunningMethods.java
line 44: " while (!stop) { count2++; }" +
line 53: while (!stop) { count1++; }
line 56: while (!stop) { count2++; }
These may not behave well on OSes with bad threading
models. You might want to add a helper function that
sleeps for 10ms and have each of these loops call it
so the test more well behaved.
Dan
bug link https://bugs.openjdk.java.net/browse/JDK-8055008
Thanks,
Coleen
