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, vm_string_table_data }; 43 44 template <WeakHandleType T> 45 class WeakHandle { 46 public: 47 private: 48 oop* _obj; 49 50 WeakHandle(oop* w) : _obj(w) {} 51 static OopStorage* get_storage(); 52 public: 53 WeakHandle() : _obj(NULL) {} // needed for init 54 55 static WeakHandle create(Handle obj); 56 inline oop resolve() const; 57 inline oop peek() const; 58 void release() const; 59 bool is_null() const { return _obj == NULL; } 60 61 void replace(oop with_obj); 62 63 void print() const; 64 void print_on(outputStream* st) const; 65 }; 66 67 typedef WeakHandle<vm_class_loader_data> ClassLoaderWeakHandle; 68 69 #endif // SHARE_VM_OOPS_WEAKHANDLE_HPP