view src/share/vm/utilities/hashtable.hpp @ 13404:46bb2774fc88

7133093: Improve system dictionary performance Summary: implement one dictionary per ClassLoaderData for faster lookup and removal during class unloading Reviewed-by: iklam, acorn, jiangli
author coleenp
date Fri, 28 Jul 2017 10:48:35 -0400
parents c044f8d03932
children a77c680f1535
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 * Copyright (c) 2003, 2017, Oracle and/or its affiliates. All rights reserved.
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 * or visit if you need additional information or have any
 * questions.


#include "classfile/classLoaderData.hpp"
#include "memory/allocation.hpp"
#include "oops/oop.hpp"
#include "oops/symbol.hpp"
#include "runtime/handles.hpp"

// This is a generic hashtable, designed to be used for the symbol
// and string tables.
// It is implemented as an open hash table with a fixed number of buckets.
// %note:
//  - TableEntrys are allocated in blocks to reduce the space overhead.

template <MEMFLAGS F> class BasicHashtableEntry : public CHeapObj<F> {
  friend class VMStructs;
  unsigned int         _hash;           // 32-bit hash for item

  // Link to next element in the linked list for this bucket.  EXCEPT
  // bit 0 set indicates that this entry is shared and must not be
  // unlinked from the table. Bit 0 is set during the dumping of the
  // archive. Since shared entries are immutable, _next fields in the
  // shared entries will not change.  New entries will always be
  // unshared and since pointers are align, bit 0 will always remain 0
  // with no extra effort.
  BasicHashtableEntry<F>* _next;

  // Windows IA64 compiler requires subclasses to be able to access these
  // Entry objects should not be created, they should be taken from the
  // free list with BasicHashtable.new_entry().
  BasicHashtableEntry() { ShouldNotReachHere(); }
  // Entry objects should not be destroyed.  They should be placed on
  // the free list instead with BasicHashtable.free_entry().
  ~BasicHashtableEntry() { ShouldNotReachHere(); }


  unsigned int hash() const             { return _hash; }
  void set_hash(unsigned int hash)      { _hash = hash; }
  unsigned int* hash_addr()             { return &_hash; }

  static BasicHashtableEntry<F>* make_ptr(BasicHashtableEntry<F>* p) {
    return (BasicHashtableEntry*)((intptr_t)p & -2);

  BasicHashtableEntry<F>* next() const {
    return make_ptr(_next);

  void set_next(BasicHashtableEntry<F>* next) {
    _next = next;

  BasicHashtableEntry<F>** next_addr() {
    return &_next;

  bool is_shared() const {
    return ((intptr_t)_next & 1) != 0;

  void set_shared() {
    _next = (BasicHashtableEntry<F>*)((intptr_t)_next | 1);

template <class T, MEMFLAGS F> class HashtableEntry : public BasicHashtableEntry<F> {
  friend class VMStructs;
  T               _literal;          // ref to item in table.

  // Literal
  T literal() const                   { return _literal; }
  T* literal_addr()                   { return &_literal; }
  void set_literal(T s)               { _literal = s; }

  HashtableEntry* next() const {
    return (HashtableEntry*)BasicHashtableEntry<F>::next();
  HashtableEntry** next_addr() {
    return (HashtableEntry**)BasicHashtableEntry<F>::next_addr();

template <MEMFLAGS F> class HashtableBucket : public CHeapObj<F> {
  friend class VMStructs;
  // Instance variable
  BasicHashtableEntry<F>*       _entry;

  // Accessing
  void clear()                        { _entry = NULL; }

  // The following methods use order access methods to avoid race
  // conditions in multiprocessor systems.
  BasicHashtableEntry<F>* get_entry() const;
  void set_entry(BasicHashtableEntry<F>* l);

  // The following method is not MT-safe and must be done under lock.
  BasicHashtableEntry<F>** entry_addr()  { return &_entry; }


template <MEMFLAGS F> class BasicHashtable : public CHeapObj<F> {
  friend class VMStructs;

  BasicHashtable(int table_size, int entry_size);
  BasicHashtable(int table_size, int entry_size,
                 HashtableBucket<F>* buckets, int number_of_entries);

  // Sharing support.
  void copy_buckets(char** top, char* end);
  void copy_table(char** top, char* end);

  // Bucket handling
  int hash_to_index(unsigned int full_hash) const {
    int h = full_hash % _table_size;
    assert(h >= 0 && h < _table_size, "Illegal hash value");
    return h;

  // Instance variables
  int               _table_size;
  HashtableBucket<F>*     _buckets;
  BasicHashtableEntry<F>* volatile _free_list;
  char*             _first_free_entry;
  char*             _end_block;
  int               _entry_size;
  volatile int      _number_of_entries;


  void initialize(int table_size, int entry_size, int number_of_entries);

  // Accessor
  int entry_size() const { return _entry_size; }

  // The following method is MT-safe and may be used with caution.
  BasicHashtableEntry<F>* bucket(int i) const;

  // The following method is not MT-safe and must be done under lock.
  BasicHashtableEntry<F>** bucket_addr(int i) { return _buckets[i].entry_addr(); }

  // Attempt to get an entry from the free list
  BasicHashtableEntry<F>* new_entry_free_list();

  // Table entry management
  BasicHashtableEntry<F>* new_entry(unsigned int hashValue);

  // Used when moving the entry to another table
  // Clean up links, but do not add to free_list
  void unlink_entry(BasicHashtableEntry<F>* entry) {

  // Move over freelist and free block for allocation
  void copy_freelist(BasicHashtable* src) {
    _free_list = src->_free_list;
    src->_free_list = NULL;
    _first_free_entry = src->_first_free_entry;
    src->_first_free_entry = NULL;
    _end_block = src->_end_block;
    src->_end_block = NULL;

  // Free the buckets in this hashtable
  void free_buckets();

  // Helper data structure containing context for the bucket entry unlink process,
  // storing the unlinked buckets in a linked list.
  // Also avoids the need to pass around these four members as parameters everywhere.
  struct BucketUnlinkContext {
    int _num_processed;
    int _num_removed;
    // Head and tail pointers for the linked list of removed entries.
    BasicHashtableEntry<F>* _removed_head;
    BasicHashtableEntry<F>* _removed_tail;

    BucketUnlinkContext() : _num_processed(0), _num_removed(0), _removed_head(NULL), _removed_tail(NULL) {

    void free_entry(BasicHashtableEntry<F>* entry);
  // Add of bucket entries linked together in the given context to the global free list. This method
  // is mt-safe wrt. to other calls of this method.
  void bulk_free_entries(BucketUnlinkContext* context);
  int table_size() { return _table_size; }
  void set_entry(int index, BasicHashtableEntry<F>* entry);

  void add_entry(int index, BasicHashtableEntry<F>* entry);

  void free_entry(BasicHashtableEntry<F>* entry);

  int number_of_entries() { return _number_of_entries; }

  template <class T> void verify_table(const char* table_name) PRODUCT_RETURN;

template <class T, MEMFLAGS F> class Hashtable : public BasicHashtable<F> {
  friend class VMStructs;

  Hashtable(int table_size, int entry_size)
    : BasicHashtable<F>(table_size, entry_size) { }

  Hashtable(int table_size, int entry_size,
                   HashtableBucket<F>* buckets, int number_of_entries)
    : BasicHashtable<F>(table_size, entry_size, buckets, number_of_entries) { }

  // Debugging
  void print()               PRODUCT_RETURN;

  unsigned int compute_hash(const Symbol* name) const {
    return (unsigned int) name->identity_hash();

  int index_for(const Symbol* name) const {
    return this->hash_to_index(compute_hash(name));


  // Table entry management
  HashtableEntry<T, F>* new_entry(unsigned int hashValue, T obj);
  // Don't create and use freelist of HashtableEntry.
  HashtableEntry<T, F>* allocate_new_entry(unsigned int hashValue, T obj);

  // The following method is MT-safe and may be used with caution.
  HashtableEntry<T, F>* bucket(int i) const {
    return (HashtableEntry<T, F>*)BasicHashtable<F>::bucket(i);

  // The following method is not MT-safe and must be done under lock.
  HashtableEntry<T, F>** bucket_addr(int i) {
    return (HashtableEntry<T, F>**)BasicHashtable<F>::bucket_addr(i);


template <class T, MEMFLAGS F> class RehashableHashtable : public Hashtable<T, F> {
 friend class VMStructs;

  enum {
    rehash_count = 100,
    rehash_multiple = 60

  // Check that the table is unbalanced
  bool check_rehash_table(int count);

  RehashableHashtable(int table_size, int entry_size)
    : Hashtable<T, F>(table_size, entry_size) { }

  RehashableHashtable(int table_size, int entry_size,
                   HashtableBucket<F>* buckets, int number_of_entries)
    : Hashtable<T, F>(table_size, entry_size, buckets, number_of_entries) { }

  // Function to move these elements into the new table.
  void move_to(RehashableHashtable<T, F>* new_table);
  static bool use_alternate_hashcode();
  static juint seed();

  static int literal_size(Symbol *symbol);
  static int literal_size(oop oop);

  // The following two are currently not used, but are needed anyway because some
  // C++ compilers (MacOS and Solaris) force the instantiation of
  // Hashtable<ConstantPool*, mtClass>::dump_table() even though we never call this function
  // in the VM code.
  static int literal_size(ConstantPool *cp) {Unimplemented(); return 0;}
  static int literal_size(Klass *k)         {Unimplemented(); return 0;}

  void dump_table(outputStream* st, const char *table_name);

  static juint _seed;

template <class T, MEMFLAGS F> juint RehashableHashtable<T, F>::_seed = 0;
template <class T, MEMFLAGS F> juint RehashableHashtable<T, F>::seed() { return _seed; };
template <class T, MEMFLAGS F> bool  RehashableHashtable<T, F>::use_alternate_hashcode() { return _seed != 0; };