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products/Sources/formale Sprachen/Java/Openjdk/src/hotspot/share/oops/ (Sun/Oracle ^©) Datei vom 13.11.2022 mit Größe 3 kB

Quelle symbolHandle.hpp Sprache: C

/*
* Copyright (c) 2022, 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
* or visit www.oracle.com if you need additional information or have any
* questions.
*
*/

#ifndef SHARE_OOPS_SYMBOLHANDLE_HPP
#define SHARE_OOPS_SYMBOLHANDLE_HPP

#include "memory/allocation.hpp"
#include "oops/symbol.hpp"

// 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() 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.
template <bool TEMP>
class SymbolHandleBase : public StackObj {
  Symbol* _temp;

public:
  SymbolHandleBase() : _temp(NULL) { }

  // Conversion from a Symbol* to a SymbolHandleBase.
  // Does not increment the current reference count if temporary.
  SymbolHandleBase(Symbol *s) : _temp(s) {
    if (!TEMP) {
      assert(s != nullptr, "must not be null");
      s->increment_refcount();
    }
  }

  // Copy constructor increments reference count.
  SymbolHandleBase(const SymbolHandleBase& rhs) : _temp(rhs._temp) {
    Symbol::maybe_increment_refcount(_temp);
  }

  // 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=(SymbolHandleBase rhs) {
    Symbol* tmp = rhs._temp;
    rhs._temp = _temp;
    _temp = tmp;
  }

  // Decrement reference counter so it can go away if it's unused
  ~SymbolHandleBase() {
    Symbol::maybe_decrement_refcount(_temp);
  }

  // Symbol* conversion operators
  Symbol* operator -> () const                   { return _temp; }
  bool    operator == (Symbol* o) const          { return _temp == o; }
  operator Symbol*() const                       { return _temp; }

  static unsigned int compute_hash(const SymbolHandleBase& name) {
    return (unsigned int) name->identity_hash();
  }
};

// TempNewSymbol is a temporary holder for a newly created symbol
using TempNewSymbol = SymbolHandleBase<true>;

// SymbolHandle is a non-temp symbol used to hold a symbol in a semi permanent place,
// like in a hashtable. The only difference is that the constructor increments the refcount.
using SymbolHandle = SymbolHandleBase<false>;

#endif // SHARE_OOPS_SYMBOLHANDLE_HPP

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