RFR(S): 8232081: Try to link all classes during dynamic CDS dump
ioi.lam at oracle.com
Thu Feb 27 05:46:01 UTC 2020
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.
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:
beforeHalt(); // native
(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
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
What do you think?
>> 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.
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