RFR 8056084: Refactor Hashtable to allow implementations without rehashing support

[Mikael Gerdin]

Hi all,

For JDK-8048268 I need to do some refactoring of the Hashtable class template.

>From the bug description:
In order to simplify usage of the Hashtable<T, F> class the code to perform 
rehashing of the SymbolTable and StringTable should be factored out to an 
intermediate class common to those two tables.
Also factor out HashtableEntry freelist allocation to allow implementors an 
easier route for providing their own memory management. 

Introducing the new intermediary superclass requires some calls to superclass 
functions to be qualified using the "this->" syntax due to the C++ template 
name lookup rules.

a comment about hashtable.cpp RehashableHashtable::dump_table:

-  int bucket_bytes = (int)num_buckets * sizeof(bucket(0));
+  int bucket_bytes = (int)num_buckets * sizeof(HashtableBucket<F>);

I decided to change the sizeof to count the size of the hashtable bucket class 
instead of the HashtableEntry* returned by bucket(0), even though they may be 
of the same size currently.

Note that the webrev url refers to another bug.
Webrev: http://cr.openjdk.java.net/~mgerdin/8048268/hashtable-refactor/webrev/
Buglink: https://bugs.openjdk.java.net/browse/JDK-8056084

Testing: JPRT.