RFR(S): 8232081: Try to link all classes during dynamic CDS dump

[Calvin Cheung]

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/

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
>>>
>