1 /*
   2  * Copyright (c) 2017, Oracle and/or its affiliates. All rights reserved.
   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   4  *
   5  * This code is free software; you can redistribute it and/or modify it
   6  * under the terms of the GNU General Public License version 2 only, as
   7  * published by the Free Software Foundation.
   8  *
   9  * This code is distributed in the hope that it will be useful, but WITHOUT
  10  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  11  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  12  * version 2 for more details (a copy is included in the LICENSE file that
  13  * accompanied this code).
  14  *
  15  * You should have received a copy of the GNU General Public License version
  16  * 2 along with this work; if not, write to the Free Software Foundation,
  17  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  18  *
  19  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  20  * or visit www.oracle.com if you need additional information or have any
  21  * questions.
  22  *
  23  */
  24 
  25 #ifndef SHARE_VM_OOPS_OOPHANDLE_HPP
  26 #define SHARE_VM_OOPS_OOPHANDLE_HPP
  27 
  28 #include "oops/oop.hpp"
  29 #include "runtime/atomic.hpp"
  30 #include "runtime/orderAccess.hpp"
  31 
  32 class outputStream;
  33 
  34 // Simple class for encapsulating oop pointers stored in metadata.
  35 // These are different from Handle.  The Handle class stores pointers
  36 // to oops on the stack, and manages the allocation from a thread local
  37 // area in the constructor.
  38 // This assumes that the caller will allocate the handle in the appropriate
  39 // area.  The reason for the encapsulation is to help with naming and to allow
  40 // future uses for read barriers.
  41 
  42 class OopHandle {
  43 private:
  44   oop* _obj;
  45 
  46 public:
  47   OopHandle() : _obj(NULL) {}
  48   OopHandle(oop* w) : _obj(w) {}
  49 
  50   oop resolve() const         { return (_obj == NULL) ? (oop)NULL : *_obj; }
  51   oop* ptr()    const { return _obj; }
  52 
  53   // For ModuleEntry the protection_domain field requires memory ordering logic.
  54   oop resolve_acquire() const { 
  55     oop* obj = (oop*)OrderAccess::load_ptr_acquire(&_obj);
  56     return (obj == NULL) ? (oop)NULL : *obj;
  57   }
  58   bool set_atomic(OopHandle value) {
  59     return (Atomic::cmpxchg_ptr(value._obj, &_obj, NULL) == NULL);
  60   }
  61 };
  62 
  63 #endif // SHARE_VM_OOPS_OOPHANDLE_HPP