Hi David, Ioi,
Here's an updated webrev which doesn't involve changing
InstanceKlass::verify_on() and made use of the changes for JDK-8240481.
http://cr.openjdk.java.net/~ccheung/jdk15/8232081/webrev.03/
thanks,
Calvin
On 3/1/20 10:14 PM, David Holmes wrote:
Hi Calvin,
On 28/02/2020 4:12 pm, Calvin Cheung wrote:
Hi David,
On 2/27/20 5:40 PM, David Holmes wrote:
Hi Calvin, Ioi,
Looking good - comments below.
A meta-question: normal application classes are rarely loaded but
not linked so I'm a little surprised this is an issue. What is the
main source of such classes - generated classes like lambda forms?
Also why do we need to link them when loading from the archive if
they were never linked when the application actually executed ??
I saw that Ioi already answered the above.
I'll try to answer your questions inline below..
Responses inline below ...
On 28/02/2020 10:48 am, Calvin Cheung wrote:
Hi David, Ioi,
Thanks for your review and suggestions.
On 2/26/20 9:46 PM, Ioi Lam wrote:
On 2/26/20 7:50 PM, David Holmes wrote:
Hi Calvin,
Adding core-libs-dev as you are messing with their code :)
On 27/02/2020 1:19 pm, Calvin Cheung wrote:
JBS: https://bugs.openjdk.java.net/browse/JDK-8232081
webrev:
http://cr.openjdk.java.net/~ccheung/jdk15/8232081/webrev.00/
The proposed changeset for this RFE adds a
JVM_LinkClassesForCDS() function to be called from
java/lang/Shutdown to notify the JVM to link the classes loaded
by the builtin class loaders. The
This would be much less disruptive if this was handled purely on
the VM side once we have started shutdown. No need to make any
changes to the Java side then, nor jvm.cpp.
Hi David,
To link the classes, we need to be able to run Java code -- when
linking a class X loaded by the app loader, X will be verified.
During verification of X, we may need to load additional classes
from the app loader, which executes Java code during its class
loading operations.
We also need to handle all the exit conditions. As far as I can
tell, an app can exit the JVM in two ways:
(1) Explicitly calling System.exit(). This will call
java.lang.Shutdown.exit() which does this:
http://hg.openjdk.java.net/jdk/jdk/file/0edc7fd0d7a3/src/java.base/share/classes/java/lang/Shutdown.java#l163
beforeHalt(); // native
runHooks();
halt(status);
(2) When all non-daemon threads have died (e.g., falling out of
the bottom of HelloWorld.main()). There's no explicit call to
System.exit(), but the JVM will proactively call
java.lang.Shutdown.shutdown() inside
JavaThread::invoke_shutdown_hooks()
http://hg.openjdk.java.net/jdk/jdk/file/0edc7fd0d7a3/src/hotspot/share/runtime/thread.cpp#l4331
http://hg.openjdk.java.net/jdk/jdk/file/0edc7fd0d7a3/src/java.base/share/classes/java/lang/Shutdown.java#l184
If we want to avoid modifying the Java code, I think we can
intercept JVM_BeforeHalt() and
JavaThread::invoke_shutdown_hooks(). This way we should be able to
handle all the classes (except those that are loaded inside
Shutdown.runHooks).
I've implemented the above. No changes to the Java side.
updated webrev:
http://cr.openjdk.java.net/~ccheung/jdk15/8232081/webrev.01/
This looks much better to me. I wasn't sure if you were that
concerned about catching the classes loaded by the Shutdown hooks,
but it is good you are not as it seems problematic to me to trigger
class loading etc after the shutdown hooks have executed - you may
hit unexpected conditions. So this approach is good.
A few minor comments:
src/hotspot/share/memory/metaspaceShared.cpp
src/hotspot/share/memory/metaspaceShared.hpp
Why the change from TRAPS to "Thread* THREAD"?
I forgot why I changed it but I've changed it back and it still works.
Ok.
---
src/hotspot/share/oops/instanceKlass.cpp
I'm not clear how verify_on is used so am unsure how the additional
error state check may affect code unrelated to dynamic dumping ??
Some of the appcds tests by design have some classes which fail
verification. Without the change, the following assert would fail:
void vtableEntry::verify(klassVtable* vt, outputStream* st) {
Klass* vtklass = vt->klass();
if (vtklass->is_instance_klass() &&
(InstanceKlass::cast(vtklass)->major_version() >=
klassVtable::VTABLE_TRANSITIVE_OVERRIDE_VERSION)) {
*assert*(method() != NULL, "must have set method");
}
Okay so you need to exclude for that case but ...
Here's the call stack during dynamic CDS dump to the above function:
vtableEntry::verify(klassVtable *, outputStream *) : void
klassVtable::verify(outputStream *, bool) : void
InstanceKlass::verify_on(outputStream *) : void
Klass::verify() : void
ClassLoaderData::verify() : void
ClassLoaderDataGraph::verify() : void
Universe::verify(enum VerifyOption, const
char *) : void
Universe::verify(const char *) : void
DynamicArchiveBuilder::verify_universe(const char *) : void
DynamicArchiveBuilder::doit() : void (2 matches)
VM_PopulateDynamicDumpSharedSpace::doit() : void
VM_Operation::evaluate() : void
The is_linked() function is implemented as:
bool is_linked() const { return _init_state >=
linked; }
which includes 'initialization_error'.
... AFAICS Universe::verify is call from a number of places, all of
which would reach this modified code. As that existing code has
included classes that are in the error state then it seems to me that
unless you can prove otherwise you need to keep the existing code
as-is for the non-CDS dump case.
A previous version of the changeset (including the change in question
in instanceKlass.cpp) passed tier1 - 4 testing. Let me know if I
should run other tests to make sure the change is good.
There may well not be a test that covers this.
Thanks,
David
Also can I suggest (as you are touching this code) to delete the
ancient comment:
3580 // $$$ This used to be done only for m/s collections. Doing it
3581 // always seemed a valid generalization. (DLD -- 6/00)
I'm glad that you suggested to remove the above comment. I've no clue
what it means either.
updated webrev:
http://cr.openjdk.java.net/~ccheung/jdk15/8232081/webrev.02/
thanks,
Calvin
Thanks,
David
-----
I also updated the test to test the shutdown hook and System.exit()
scenarios.
All appcds tests passed on my linux host. I'll run more tests using
mach5.
thanks,
Calvin
What do you think?
- Ioi
Thanks,
David
MetaspaceShared::link_and_cleanup_shared_classes() has been
modified to handle both static and dynamic CDS dump. For dynamic
CDS dump, only classes loaded by the builtin class loaders will
be linked. Local performance testing using javac on
HelloWorld.java shows an improvement of >5%.
Passed tier1 - 4 tests.
thanks,
Calvin
