src/hotspot/share/classfile/stringTable.hpp

/*
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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * 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.
 *
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#ifndef SHARE_CLASSFILE_STRINGTABLE_HPP
#define SHARE_CLASSFILE_STRINGTABLE_HPP

#include "memory/allocation.hpp"
#include "memory/padded.hpp"
#include "oops/oop.hpp"
#include "oops/oopHandle.hpp"
#include "oops/weakHandle.hpp"
#include "utilities/tableStatistics.hpp"

class CompactHashtableWriter;
class DumpedInternedStrings;
class JavaThread;
class SerializeClosure;

class StringTable;
class StringTableConfig;
class StringTableCreateEntry;

class StringTable : public CHeapObj<mtSymbol>{
  friend class VMStructs;
  friend class Symbol;
  friend class StringTableConfig;
  friend class StringTableCreateEntry;

  static volatile bool _has_work;

  // Set if one bucket is out of balance due to hash algorithm deficiency
  static volatile bool _needs_rehashing;

  static OopStorage* _oop_storage;

  static void grow(JavaThread* jt);
  static void clean_dead_entries(JavaThread* jt);

  static double get_load_factor();
  static double get_dead_factor(size_t num_dead);

  // GC support

  // Callback for GC to notify of changes that might require cleaning or resize.
  static void gc_notification(size_t num_dead);
  static void trigger_concurrent_work();

  static size_t item_added();
  static void item_removed();

  static oop intern(Handle string_or_null_h, const jchar* name, int len, TRAPS);
  static oop do_intern(Handle string_or_null, const jchar* name, int len, uintx hash, TRAPS);
  static oop do_lookup(const jchar* name, int len, uintx hash);

  static void print_table_statistics(outputStream* st);

  static bool do_rehash();

 public:
  static size_t table_size();
  static TableStatistics get_table_statistics();

  static void create_table();

  static void do_concurrent_work(JavaThread* jt);
  static bool has_work();

  // Probing
  static oop lookup(Symbol* symbol);
  static oop lookup(const jchar* chars, int length);

  // Interning
  static oop intern(Symbol* symbol, TRAPS);
  static oop intern(oop string, TRAPS);
  static oop intern(const char *utf8_string, TRAPS);

  // Rehash the string table if it gets out of balance
private:
  static bool should_grow();

public:
  static bool rehash_table_expects_safepoint_rehashing();
  static void rehash_table();
  static bool needs_rehashing() { return _needs_rehashing; }
  static inline void update_needs_rehash(bool rehash) {
    if (rehash) {
      _needs_rehashing = true;
    }
  }

  // Sharing
#if INCLUDE_CDS_JAVA_HEAP
  static inline oop read_string_from_compact_hashtable(address base_address, u4 index);

private:
  static bool _is_two_dimensional_shared_strings_array;
  static OopHandle _shared_strings_array;
  static int _shared_strings_array_root_index;

  // All the shared strings are referenced through _shared_strings_array to keep them alive.
  // Each shared string is stored as a 32-bit index in ::_shared_table. The index
  // is interpreted in two ways:
  //
  // [1] _is_two_dimensional_shared_strings_array = false: _shared_strings_array is an Object[].
  //     Each shared string is stored as _shared_strings_array[index]
  //
  // [2] _is_two_dimensional_shared_strings_array = true: _shared_strings_array is an Object[][]
  //     This happens when there are too many elements in the shared table. We store them
  //     using two levels of objArrays, such that none of the arrays are too big for
  //     ArchiveHeapWriter::is_too_large_to_archive(). In this case, the index is splited into two
  //     parts. Each shared string is stored as _shared_strings_array[primary_index][secondary_index]:
  //
  //           [bits 31 .. 14][ bits 13 .. 0  ]
  //            primary_index  secondary_index
  const static int _secondary_array_index_bits = 14;
  const static int _secondary_array_max_length = 1 << _secondary_array_index_bits;
  const static int _secondary_array_index_mask = _secondary_array_max_length - 1;

  // make sure _secondary_array_index_bits is not too big
  static void verify_secondary_array_index_bits() PRODUCT_RETURN;
#endif // INCLUDE_CDS_JAVA_HEAP

 private:
  static oop lookup_shared(const jchar* name, int len, unsigned int hash) NOT_CDS_JAVA_HEAP_RETURN_(nullptr);
 public:
  static oop lookup_shared(const jchar* name, int len) NOT_CDS_JAVA_HEAP_RETURN_(nullptr);
  static size_t shared_entry_count() NOT_CDS_JAVA_HEAP_RETURN_(0);
  static void allocate_shared_strings_array(TRAPS) NOT_CDS_JAVA_HEAP_RETURN;
  static oop init_shared_table(const DumpedInternedStrings* dumped_interned_strings) NOT_CDS_JAVA_HEAP_RETURN_(nullptr);
  static void set_shared_strings_array_index(int root_index) NOT_CDS_JAVA_HEAP_RETURN;
  static void serialize_shared_table_header(SerializeClosure* soc) NOT_CDS_JAVA_HEAP_RETURN;

  // Jcmd
  static void dump(outputStream* st, bool verbose=false);
  // Debugging
  static size_t verify_and_compare_entries();
  static void verify();
};

#endif // SHARE_CLASSFILE_STRINGTABLE_HPP