RFR: 8184603: Create ObjectStreamField signature lazily when possible
claes.redestad at oracle.com
Mon Jul 17 12:16:11 UTC 2017
On 2017-07-15 14:08, Peter Levart wrote:
> It seems that interning signature(s) is important for correctness (for
> example, in ObjectOutputStream.writeTypeString(str) the 'str' is used
> to lookup a handle so that handles are put into stream instead of the
> type signature(s) for multiple references to the same type). Looking
> up objects in handles table is based on identity comparison.
Yes, interned signatures is important for correctness (and performance?)
of the current serialization implementation.
> But there might be a way to obtain a singleton signature String per
> type and still profit. By adding a field to java.lang.Class and
> caching the JVM signature there. This would also be a useful public
> method, don't you think?
I have a nagging feeling that we should be careful about leaking
implementation details about the underlying VM through public APIs,
since making changes to various specifications is hard enough as it is.
> Out of 191 ObjectStreamField constructions I found in JDK sources,
> there are only 39 distinct field types involved, so the number if
> intern() calls is reduced by a factor of ~5. There's no need to cache
> signature in ObjectStreamField(s) this way any more, but there must
> still be a single final field for ObjectStreamField(s) constructed
> with explicit signature(s).
> Here's how this looks like in code:
Could this be done as a ClassValue instead of another field on Class? My
guess is only a small number of classes in any given app will be directly
involved in serialization, so growing Class seems to be a pessimization.
> What do you think?
I wonder what workloads actually see a bottleneck in these String.intern
calls, and *which* String.intern calls we are bottlenecking on in these
workloads. There's still a couple of constructors here that won't see a
I think we need more data to ensure this is actually worthwhile to pursue,
or whether there are other optimizations on a higher level that could
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