/*

 * Copyright (c) 1997, 2017, Oracle and/or its affiliates. All rights reserved.

 * 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.

 *

 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

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 */

#ifndef SHARE_VM_CLASSFILE_SYMBOLTABLE_HPP

#define SHARE_VM_CLASSFILE_SYMBOLTABLE_HPP

#include "memory/allocation.inline.hpp"

#include "oops/symbol.hpp"

#include "utilities/hashtable.hpp"

// The symbol table holds all Symbol*s and corresponding interned strings.

// Symbol*s and literal strings should be canonicalized.

//

// The interned strings are created lazily.

//

// It is implemented as an open hash table with a fixed number of buckets.

//

// %note:

//  - symbolTableEntrys are allocated in blocks to reduce the space overhead.

class BoolObjectClosure;

class outputStream;

class SerializeClosure;

// TempNewSymbol acts as a handle class in a handle/body idiom and is

// responsible for proper resource management of the body (which is a Symbol*).

// The body is resource managed by a reference counting scheme.

// TempNewSymbol can therefore be used to properly hold a newly created or referenced

// Symbol* temporarily in scope.

//

// Routines in SymbolTable will initialize the reference count of a Symbol* before

// it becomes "managed" by TempNewSymbol instances. As a handle class, TempNewSymbol

// needs to maintain proper reference counting in context of copy semantics.

//

// In SymbolTable, new_symbol() and lookup() will create a Symbol* if not already in the

// symbol table and add to the symbol's reference count.

// probe() and lookup_only() will increment the refcount if symbol is found.

class TempNewSymbol : public StackObj {

  Symbol* _temp;

 public:

  TempNewSymbol() : _temp(NULL) {}

  // Conversion from a Symbol* to a TempNewSymbol.

  // Does not increment the current reference count.

  TempNewSymbol(Symbol *s) : _temp(s) {}

  // Copy constructor increments reference count.

  TempNewSymbol(const TempNewSymbol& rhs) : _temp(rhs._temp) {

    if (_temp != NULL) {

      _temp->increment_refcount();

    }

  }

  // Assignment operator uses a c++ trick called copy and swap idiom.

  // rhs is passed by value so within the scope of this method it is a copy.

  // At method exit it contains the former value of _temp, triggering the correct refcount

  // decrement upon destruction.

  void operator=(TempNewSymbol rhs) {

    Symbol* tmp = rhs._temp;

    rhs._temp = _temp;

    _temp = tmp;

  }

  // Decrement reference counter so it can go away if it's unused

  ~TempNewSymbol() {

    if (_temp != NULL) {

      _temp->decrement_refcount();

    }

  }

  // Symbol* conversion operators

  Symbol* operator -> () const                   { return _temp; }

  bool    operator == (Symbol* o) const          { return _temp == o; }

  operator Symbol*()                             { return _temp; }

};

template <class T, class N> class CompactHashtable;

class SymbolTable : public RehashableHashtable<Symbol*, mtSymbol> {

  friend class VMStructs;

  friend class ClassFileParser;

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 bool _lookup_shared_first;

  // For statistics

  static int _symbols_removed;

  static int _symbols_counted;

  // shared symbol table.

  static CompactHashtable<Symbol*, char> _shared_table;

  Symbol* allocate_symbol(const u1* name, int len, bool c_heap, TRAPS); // Assumes no characters larger than 0x7F

  // Adding elements

  Symbol* basic_add(int index, u1* name, int len, unsigned int hashValue,

                    bool c_heap, TRAPS);

  bool basic_add(ClassLoaderData* loader_data,

                 const constantPoolHandle& cp, int names_count,

                 const char** names, int* lengths, int* cp_indices,

                 unsigned int* hashValues, TRAPS);

  static void new_symbols(ClassLoaderData* loader_data,

                          const constantPoolHandle& cp, int names_count,

                          const char** name, int* lengths,

                          int* cp_indices, unsigned int* hashValues,

                          TRAPS) {

    add(loader_data, cp, names_count, name, lengths, cp_indices, hashValues, THREAD);

  }

  static Symbol* lookup_shared(const char* name, int len, unsigned int hash);

  Symbol* lookup_dynamic(int index, const char* name, int len, unsigned int hash);

  Symbol* lookup(int index, const char* name, int len, unsigned int hash);

  SymbolTable()

    : RehashableHashtable<Symbol*, mtSymbol>(SymbolTableSize, sizeof (HashtableEntry<Symbol*, mtSymbol>)) {}

  SymbolTable(HashtableBucket<mtSymbol>* t, int number_of_entries)

    : RehashableHashtable<Symbol*, mtSymbol>(SymbolTableSize, sizeof (HashtableEntry<Symbol*, mtSymbol>), t,

                number_of_entries) {}

  // Arena for permanent symbols (null class loader) that are never unloaded

  static Arena*  _arena;

  static Arena* arena() { return _arena; }  // called for statistics

  static void initialize_symbols(int arena_alloc_size = 0);

  static volatile int _parallel_claimed_idx;

  typedef SymbolTable::BucketUnlinkContext BucketUnlinkContext;

  // Release any dead symbols. Unlinked bucket entries are collected in the given

  // context to be freed later.

  // This allows multiple threads to work on the table at once.

  static void buckets_unlink(int start_idx, int end_idx, BucketUnlinkContext* context);

public:

  enum {

    symbol_alloc_batch_size = 8,

    // Pick initial size based on java -version size measurements

    symbol_alloc_arena_size = 360*K

  };

  // The symbol table

  static SymbolTable* the_table() { return _the_table; }

  // Size of one bucket in the string table.  Used when checking for rollover.

  static uint bucket_size() { return sizeof(HashtableBucket<mtSymbol>); }

  static void create_table() {

    assert(_the_table == NULL, "One symbol table allowed.");

    _the_table = new SymbolTable();

    initialize_symbols(symbol_alloc_arena_size);

  }

  static unsigned int hash_symbol(const char* s, int len);

  static unsigned int hash_shared_symbol(const char* s, int len);

  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);

  // Only copy to C string to be added if lookup failed.

  static Symbol* lookup(const Symbol* sym, int begin, int end, TRAPS);

  static void release(Symbol* sym);

  // Look up the address of the literal in the SymbolTable for this Symbol*

  static Symbol** lookup_symbol_addr(Symbol* sym);

  // jchar (UTF16) version of lookups

  static Symbol* lookup_unicode(const jchar* name, int len, TRAPS);

  static Symbol* lookup_only_unicode(const jchar* name, int len, unsigned int& hash);

  static void add(ClassLoaderData* loader_data,

                  const constantPoolHandle& cp, int names_count,

                  const char** names, int* lengths, int* cp_indices,

                  unsigned int* hashValues, TRAPS);

  // Release any dead symbols

  static void unlink() {

    int processed = 0;

    int removed = 0;

    unlink(&processed, &removed);

  }

  static void unlink(int* processed, int* removed);

  // Release any dead symbols, possibly parallel version

  static void possibly_parallel_unlink(int* processed, int* removed);

  // iterate over symbols

  static void symbols_do(SymbolClosure *cl);

  static void metaspace_pointers_do(MetaspaceClosure* it);

  // Symbol creation

  static Symbol* new_symbol(const char* utf8_buffer, int length, TRAPS) {

    assert(utf8_buffer != NULL, "just checking");

    return lookup(utf8_buffer, length, THREAD);

  }

  static Symbol*       new_symbol(const char* name, TRAPS) {

    return new_symbol(name, (int)strlen(name), THREAD);

  }

  static Symbol*       new_symbol(const Symbol* sym, int begin, int end, TRAPS) {

    assert(begin <= end && end <= sym->utf8_length(), "just checking");

    return lookup(sym, begin, end, THREAD);

  }

  // Create a symbol in the arena for symbols that are not deleted

  static Symbol* new_permanent_symbol(const char* name, TRAPS);

  // Symbol lookup

  static Symbol* lookup(int index, const char* name, int len, TRAPS);

  // Needed for preloading classes in signatures when compiling.

  // Returns the symbol is already present in symbol table, otherwise

  // NULL.  NO ALLOCATION IS GUARANTEED!

  static Symbol* probe(const char* name, int len) {

    unsigned int ignore_hash;

    return lookup_only(name, len, ignore_hash);

  }

  static Symbol* probe_unicode(const jchar* name, int len) {

    unsigned int ignore_hash;

    return lookup_only_unicode(name, len, ignore_hash);

  }

  // Histogram

  static void print_histogram()     PRODUCT_RETURN;

  static void print()     PRODUCT_RETURN;

  // Debugging

  static void verify();

  static void dump(outputStream* st, bool verbose=false);

  static void read(const char* filename, TRAPS);

  // Sharing

  static void write_to_archive();

  static void serialize(SerializeClosure* soc);

  static u4 encode_shared(Symbol* sym);

  static Symbol* decode_shared(u4 offset);

  // Rehash the symbol table if it gets out of balance

  static void rehash_table();

  static bool needs_rehashing()         { return _needs_rehashing; }

  // Parallel chunked scanning

  static void clear_parallel_claimed_index() { _parallel_claimed_idx = 0; }

  static int parallel_claimed_index()        { return _parallel_claimed_idx; }

};

#endif // SHARE_VM_CLASSFILE_SYMBOLTABLE_HPP