7158800: Improve storage of symbol tables

Use an alternate version of hashing algorithm for symbol string tables and after a certain bucket size to improve performance

Reviewed-by: pbk, kamg, dlong, kvn, fparain

hotspot/src/share/vm/classfile/symbolTable.hpp

@@ -40,6 +40,7 @@
 //  - symbolTableEntrys are allocated in blocks to reduce the space overhead.
 
 class BoolObjectClosure;
+class outputStream;
 
 
 // Class to hold a newly created or referenced Symbol* temporarily in scope.
@@ -78,6 +79,10 @@ private:
   // The symbol table
   static SymbolTable* _the_table;
 
+  // Set if one bucket is out of balance due to hash algorithm deficiency
+  static bool _needs_rehashing;
+  static jint _seed;
+
   // For statistics
   static int symbols_removed;
   static int symbols_counted;
@@ -119,6 +124,11 @@ private:
   static Arena* arena() { return _arena; }  // called for statistics
 
   static void initialize_symbols(int arena_alloc_size = 0);
+
+  static bool use_alternate_hashcode()  { return _seed != 0; }
+  static jint seed()                    { return _seed; }
+
+  unsigned int new_hash(Symbol* sym);
 public:
   enum {
     symbol_alloc_batch_size = 8,
@@ -146,6 +156,8 @@ public:
     initialize_symbols();
   }
 
+  static unsigned int hash_symbol(const char* s, int len, unsigned int hashValue = 0);
+
   static Symbol* lookup(const char* name, int len, TRAPS);
   // lookup only, won't add. Also calculate hash.
   static Symbol* lookup_only(const char* name, int len, unsigned int& hash);
@@ -208,6 +220,7 @@ public:
 
   // Debugging
   static void verify();
+  static void dump(outputStream* st);
 
   // Sharing
   static void copy_buckets(char** top, char*end) {
@@ -219,8 +232,13 @@ public:
   static void reverse(void* boundary = NULL) {
     the_table()->Hashtable<Symbol*>::reverse(boundary);
   }
+
+  // Rehash the symbol table if it gets out of balance
+  static void rehash_table();
+  static bool needs_rehashing()         { return _needs_rehashing; }
 };
 
+
 class StringTable : public Hashtable<oop> {
   friend class VMStructs;
 
@@ -228,6 +246,10 @@ private:
   // The string table
   static StringTable* _the_table;
 
+  // Set if one bucket is out of balance due to hash algorithm deficiency
+  static bool _needs_rehashing;
+  static jint _seed;
+
   static oop intern(Handle string_or_null, jchar* chars, int length, TRAPS);
   oop basic_add(int index, Handle string_or_null, jchar* name, int len,
                 unsigned int hashValue, TRAPS);
@@ -241,6 +263,10 @@ private:
     : Hashtable<oop>((int)StringTableSize, sizeof (HashtableEntry<oop>), t,
                      number_of_entries) {}
 
+  static bool use_alternate_hashcode()  { return _seed != 0; }
+  static jint seed()                    { return _seed; }
+
+  unsigned int new_hash(oop s);
 public:
   // The string table
   static StringTable* the_table() { return _the_table; }
@@ -265,6 +291,14 @@ public:
   // Invoke "f->do_oop" on the locations of all oops in the table.
   static void oops_do(OopClosure* f);
 
+  // Hashing algorithm, used as the hash value used by the
+  //     StringTable for bucket selection and comparison (stored in the
+  //     HashtableEntry structures).  This is used in the String.intern() method.
+  static unsigned int hash_string(const jchar* s, int len, unsigned int hashValue = 0);
+
+  // Internal test.
+  static void test_alt_hash() PRODUCT_RETURN;
+
   // Probing
   static oop lookup(Symbol* symbol);
 
@@ -275,6 +309,7 @@ public:
 
   // Debugging
   static void verify();
+  static void dump(outputStream* st);
 
   // Sharing
   static void copy_buckets(char** top, char*end) {
@@ -286,6 +321,9 @@ public:
   static void reverse() {
     the_table()->Hashtable<oop>::reverse();
   }
-};
 
+  // Rehash the symbol table if it gets out of balance
+  static void rehash_table();
+  static bool needs_rehashing() { return _needs_rehashing; }
+};
 #endif // SHARE_VM_CLASSFILE_SYMBOLTABLE_HPP