RFR: 8241958: Slow ClassLoaderReferenceImpl.findType

[Egor Ushakov]

Hi all, please review the fix

The com.sun.tools.jdi.ClassLoaderReferenceImpl#findType may be slow 
because ClassLoaderReferenceImpl#visibleClasses does not populate 
signature and we check it for every class in the loop just after, so 
requesting all unavailable signatures one by one.
The fix adds extra check in classesBySignature before comparing 
signatures of all visible classes.

bugid https://bugs.openjdk.java.net/browse/JDK-8241958
cr http://cr.openjdk.java.net/~eushakov/8241958/webrev.00/

Thanks!

-- 
Egor Ushakov
Software Developer
JetBrains
http://www.jetbrains.com
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