1 /*

     2  * Copyright (c) 2018, 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_WEAKHANDLE_HPP

    26 #define SHARE_VM_OOPS_WEAKHANDLE_HPP

    27 

    28 #include "oops/oop.hpp"

    29 #include "runtime/handles.hpp"

    30 

    31 class outputStream;

    32 class OopStorage;

    33 

    34 // A WeakHandle is a pointer to an oop that is stored in an OopStorage that is

    35 // processed weakly by GC.  The runtime structures that point to the oop must

    36 // either peek or resolve the oop, the latter will keep the oop alive for

    37 // the GC cycle.  The runtime structures that reference the oop must test

    38 // if the value is NULL.  If it is NULL, it has been cleaned out by GC.

    39 // This is the vm version of jweak but has different GC lifetimes and policies,

    40 // depending on the type.

    41 

    42 enum WeakHandleType { vm_class_loader_data, vm_string };

    43 

    44 template <WeakHandleType T>

    45 class WeakHandle {

    46  public:

    47 

    48  private:

    49   oop* _obj;

    50 

    51   WeakHandle(oop* w) : _obj(w) {}

    52   static OopStorage* get_storage();

    53  public:

    54   WeakHandle() : _obj(NULL) {} // needed for init

    55 

    56   static WeakHandle create(Handle obj);

    57   inline oop resolve() const;

    58   inline oop peek() const;

    59   void release() const;

    60   bool is_null() const { return _obj == NULL; }

    61 

    62   void print() const;

    63   void print_on(outputStream* st) const;

    64 };

    65 

    66 #endif // SHARE_VM_OOPS_WEAKHANDLE_HPP