RFR: 8207263: Store the Configuration for system modules into CDS archive
claes.redestad at oracle.com
Sat Aug 4 16:22:14 UTC 2018
Jiangli and I discussed a subtle issue with the archiving changes here
last week (she's currently on vacation, and I was at JVMLS this week, so
it was never brought to the list, sorry!)
Basically: the empty configuration uses things like
Collections.emptySet(), which means it will end up deserializing an
object from the archive that doesn't (necessarily) have the same
identity as the object retrieved from direct uses of Collection.emptySet().
Same goes for the Set.of()/Map.of()/List.of() singletons which might now
already exist at runtime in two versions since the change to archive
This glitch is probably fine semantically for most intents and purposes,
but could lead to some unnecessary inefficiencies and theoretically real
surprises/bugs, so we probably need to ensure that all singletons we
serialize retain the property that they are identical to the object a
caller of the respective getter would receive.
I think this can be deferred to a must-fix follow-up, mainly since
there's some benefit in first cleaning up a few things here first:
- currently we have uses of both Collections.emptyFoo() and Foo.of() in
the ModuleDescriptor/Configuration code
- to be correct, we thus need to archive the Collections.emptyFoo()
singletons *and* the various java.util.ImmutableCollections ones
- if we first consolidated all uses of Collections.emptyFoo() to
Foo.of() (in java.lang.module), we'd only need to archive the immutable
singletons in java.util.ImmutableCollections
Consolidating to Foo.of() was actually already being considered anyway,
so I'll go ahead with a separate RFE..
On 2018-07-20 20:31, Jiangli Zhou wrote:
> Many thanks to Alan and Claes for discussions and contributions to
> this change!
> Webrev: http://cr.openjdk.java.net/~jiangli/8207263/webrev.00/
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