RFR: 8006593: Performance and compatibility improvements to hash based Map implementations

[Mike Duigou]

Hello all;

The alternative hashing implementation introduced in 7u6 added an unfortunate bottleneck to the initialization of HashMap and Hashtable instances. This patch avoids the performance bottleneck of using a shared Random instance by using a ThreadLocalRandom instead.

Along with this change are some additional performance improvements to further reduce the overhead of the alternative hashing feature and generally improve the performance of Hashtable or HashMap.

http://cr.openjdk.java.net/~mduigou/JDK-8006593/3/webrev/

Once review is completed here this patch will be proposed to JDK7u-dev for integration into the next 7u performance/feature release.

Mike