1 /* 2 * Copyright (c) 2021 Huawei Device Co., Ltd. 3 * Licensed under the Apache License, Version 2.0 (the "License"); 4 * you may not use this file except in compliance with the License. 5 * You may obtain a copy of the License at 6 * 7 * http://www.apache.org/licenses/LICENSE-2.0 8 * 9 * Unless required by applicable law or agreed to in writing, software 10 * distributed under the License is distributed on an "AS IS" BASIS, 11 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 12 * See the License for the specific language governing permissions and 13 * limitations under the License. 14 */ 15 16 #ifndef ECMASCRIPT_MEM_MARK_WORD_H 17 #define ECMASCRIPT_MEM_MARK_WORD_H 18 19 #include <cstdint> 20 #include <atomic> 21 22 #include "libpandabase/utils/bit_field.h" 23 24 namespace panda { 25 namespace ecmascript { 26 class TaggedObject; 27 class JSHClass; 28 29 using MarkWordType = uint64_t; 30 31 class MarkWord { 32 public: 33 // ForwardingAddress mark, this object has been moved and the address points to the newly allocated space. 34 static constexpr MarkWordType TAG_MARK_BIT = 0x02ULL; 35 MarkWord(TaggedObject * header)36 explicit MarkWord(TaggedObject *header) 37 { 38 value_ = reinterpret_cast<volatile std::atomic<MarkWordType> *>(header)->load(std::memory_order_acquire); 39 } 40 ~MarkWord() = default; 41 NO_COPY_SEMANTIC(MarkWord); 42 NO_MOVE_SEMANTIC(MarkWord); 43 IsForwardingAddress()44 bool IsForwardingAddress() 45 { 46 return (value_ & TAG_MARK_BIT) != 0; 47 } 48 ToForwardingAddress()49 TaggedObject *ToForwardingAddress() 50 { 51 return reinterpret_cast<TaggedObject *>(value_ & (~TAG_MARK_BIT)); 52 } 53 FromForwardingAddress(MarkWordType forwardAddress)54 static MarkWordType FromForwardingAddress(MarkWordType forwardAddress) 55 { 56 return forwardAddress | TAG_MARK_BIT; 57 } 58 GetValue()59 MarkWordType GetValue() const 60 { 61 return value_; 62 } 63 GetJSHClass()64 JSHClass *GetJSHClass() const 65 { 66 return reinterpret_cast<JSHClass *>(value_ & (~TAG_MARK_BIT)); 67 } 68 69 private: 70 MarkWordType value_ {0}; 71 }; 72 } // namespace ecmascript 73 } // namespace panda 74 75 #endif // ECMASCRIPT_MEM_MARK_WORD_H 76