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 "utils/bit_field.h" 23 #include "libpandabase/mem/mem.h" 24 25 namespace panda { 26 namespace ecmascript { 27 class TaggedObject; 28 class JSHClass; 29 30 using MarkWordType = uint64_t; 31 32 class MarkWord { 33 public: 34 // ForwardingAddress mark, this object has been moved and the address points to the newly allocated space. 35 static constexpr MarkWordType TAG_MARK_BIT = 0x02ULL; 36 MarkWord(TaggedObject * header)37 explicit MarkWord(TaggedObject *header) 38 { 39 value_ = reinterpret_cast<volatile std::atomic<MarkWordType> *>(header)->load(std::memory_order_acquire); 40 } 41 ~MarkWord() = default; 42 NO_COPY_SEMANTIC(MarkWord); 43 NO_MOVE_SEMANTIC(MarkWord); 44 IsForwardingAddress()45 bool IsForwardingAddress() 46 { 47 return (value_ & TAG_MARK_BIT) != 0; 48 } 49 ToForwardingAddress()50 TaggedObject *ToForwardingAddress() 51 { 52 return reinterpret_cast<TaggedObject *>(value_ & (~TAG_MARK_BIT)); 53 } 54 FromForwardingAddress(MarkWordType forwardAddress)55 static MarkWordType FromForwardingAddress(MarkWordType forwardAddress) 56 { 57 return forwardAddress | TAG_MARK_BIT; 58 } 59 GetValue()60 MarkWordType GetValue() const 61 { 62 return value_; 63 } 64 GetJSHClass()65 JSHClass *GetJSHClass() const 66 { 67 return reinterpret_cast<JSHClass *>(value_ & (~TAG_MARK_BIT)); 68 } 69 70 private: 71 MarkWordType value_{0}; 72 }; 73 } // namespace ecmascript 74 } // namespace panda 75 76 #endif // ECMASCRIPT_MEM_MARK_WORD_H 77