RFR(S) 8218700: infinite loop in HotSpotJVMCIMetaAccessContext.fromClass after OutOfMemoryError

Tom Rodriguez tom.rodriguez at oracle.com
Fri May 3 17:45:02 UTC 2019

dean.long at oracle.com wrote on 5/2/19 11:47 PM:
> On 5/1/19 5:44 PM, Tom Rodriguez wrote:
>> You'll need to update your webrev after Vladimir's push.  This code 
>> has moved into HotSpootJVMCIRuntime.java.
> Here's the updated version:
> http://cr.openjdk.java.net/~dlong/8218700/webrev.3/

Looks good to me.

>> Maybe WeakReferenceHolder instead of WeakTypeRef?  It needs a comment 
>> explaining that we're intentionally avoiding the use of 
>> ClassValue.remove as well.  Shouldn't the ref field be volatile? 
>> ClassValue includes some barrier semantics and the new code needs 
>> similar guarantees.
> I went ahead and made it volatile, but I don't understand what guarantee 
> was missing, and what problem we want to eliminate, unless it is to 
> reduce the possibility of duplicates.  But the fix for JDK-8201248 
> assumes that duplicates are possible, so I wasn't worried about that.

We're publishing a mutable locally created object to other threads so it 
seems like we need some sort of ordering barrier when we do so. 
Presumably the ClassValue would normally provide some ordering though 
it's a little unclear from the javadoc if it makes any such guarantees. 
Is the extra volatile unneeded?


> dl
>> tom
>> dean.long at oracle.com wrote on 4/26/19 12:09 PM:
>>> https://bugs.openjdk.java.net/browse/JDK-8218700
>>> http://cr.openjdk.java.net/~dlong/8218700/webrev.2/
>>> If we throw an OutOfMemoryError in the right place (see JDK-8222941), 
>>> HotSpotJVMCIMetaAccessContext.fromClass can go into an infinite loop 
>>> calling ClassValue.remove.  To work around the problem, reset the 
>>> value in a mutable cell instead of calling remove.
>>> dl

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