1 /* 2 * Copyright (C) 2011 The Android Open Source Project 3 * 4 * Licensed under the Apache License, Version 2.0 (the "License"); 5 * you may not use this file except in compliance with the License. 6 * You may obtain a copy of the License at 7 * 8 * http://www.apache.org/licenses/LICENSE-2.0 9 * 10 * Unless required by applicable law or agreed to in writing, software 11 * distributed under the License is distributed on an "AS IS" BASIS, 12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 13 * See the License for the specific language governing permissions and 14 * limitations under the License. 15 */ 16 17 #ifndef ART_RUNTIME_LOCK_WORD_H_ 18 #define ART_RUNTIME_LOCK_WORD_H_ 19 20 #include <iosfwd> 21 #include <stdint.h> 22 23 #include "base/logging.h" 24 #include "utils.h" 25 26 namespace art { 27 namespace mirror { 28 class Object; 29 } // namespace mirror 30 31 class Monitor; 32 33 /* The lock value itself as stored in mirror::Object::monitor_. The two most significant bits of 34 * the state. The three possible states are fat locked, thin/unlocked, and hash code. 35 * When the lock word is in the "thin" state and its bits are formatted as follows: 36 * 37 * |33|22222222221111|1111110000000000| 38 * |10|98765432109876|5432109876543210| 39 * |00| lock count |thread id owner | 40 * 41 * When the lock word is in the "fat" state and its bits are formatted as follows: 42 * 43 * |33|222222222211111111110000000000| 44 * |10|987654321098765432109876543210| 45 * |01| MonitorId | 46 * 47 * When the lock word is in hash state and its bits are formatted as follows: 48 * 49 * |33|222222222211111111110000000000| 50 * |10|987654321098765432109876543210| 51 * |10| HashCode | 52 */ 53 class LockWord { 54 public: 55 enum { 56 // Number of bits to encode the state, currently just fat or thin/unlocked or hash code. 57 kStateSize = 2, 58 // Number of bits to encode the thin lock owner. 59 kThinLockOwnerSize = 16, 60 // Remaining bits are the recursive lock count. 61 kThinLockCountSize = 32 - kThinLockOwnerSize - kStateSize, 62 // Thin lock bits. Owner in lowest bits. 63 64 kThinLockOwnerShift = 0, 65 kThinLockOwnerMask = (1 << kThinLockOwnerSize) - 1, 66 // Count in higher bits. 67 kThinLockCountShift = kThinLockOwnerSize + kThinLockOwnerShift, 68 kThinLockCountMask = (1 << kThinLockCountSize) - 1, 69 kThinLockMaxCount = kThinLockCountMask, 70 71 // State in the highest bits. 72 kStateShift = kThinLockCountSize + kThinLockCountShift, 73 kStateMask = (1 << kStateSize) - 1, 74 kStateThinOrUnlocked = 0, 75 kStateFat = 1, 76 kStateHash = 2, 77 kStateForwardingAddress = 3, 78 79 // When the state is kHashCode, the non-state bits hold the hashcode. 80 kHashShift = 0, 81 kHashSize = 32 - kStateSize, 82 kHashMask = (1 << kHashSize) - 1, 83 }; 84 FromThinLockId(uint32_t thread_id,uint32_t count)85 static LockWord FromThinLockId(uint32_t thread_id, uint32_t count) { 86 CHECK_LE(thread_id, static_cast<uint32_t>(kThinLockOwnerMask)); 87 return LockWord((thread_id << kThinLockOwnerShift) | (count << kThinLockCountShift) | 88 (kStateThinOrUnlocked << kStateShift)); 89 } 90 FromForwardingAddress(size_t target)91 static LockWord FromForwardingAddress(size_t target) { 92 DCHECK(IsAligned < 1 << kStateSize>(target)); 93 return LockWord((target >> kStateSize) | (kStateForwardingAddress << kStateShift)); 94 } 95 FromHashCode(uint32_t hash_code)96 static LockWord FromHashCode(uint32_t hash_code) { 97 CHECK_LE(hash_code, static_cast<uint32_t>(kHashMask)); 98 return LockWord((hash_code << kHashShift) | (kStateHash << kStateShift)); 99 } 100 101 enum LockState { 102 kUnlocked, // No lock owners. 103 kThinLocked, // Single uncontended owner. 104 kFatLocked, // See associated monitor. 105 kHashCode, // Lock word contains an identity hash. 106 kForwardingAddress, // Lock word contains the forwarding address of an object. 107 }; 108 GetState()109 LockState GetState() const { 110 if (UNLIKELY(value_ == 0)) { 111 return kUnlocked; 112 } else { 113 uint32_t internal_state = (value_ >> kStateShift) & kStateMask; 114 switch (internal_state) { 115 case kStateThinOrUnlocked: 116 return kThinLocked; 117 case kStateHash: 118 return kHashCode; 119 case kStateForwardingAddress: 120 return kForwardingAddress; 121 default: 122 DCHECK_EQ(internal_state, static_cast<uint32_t>(kStateFat)); 123 return kFatLocked; 124 } 125 } 126 } 127 128 // Return the owner thin lock thread id. 129 uint32_t ThinLockOwner() const; 130 131 // Return the number of times a lock value has been locked. 132 uint32_t ThinLockCount() const; 133 134 // Return the Monitor encoded in a fat lock. 135 Monitor* FatLockMonitor() const; 136 137 // Return the forwarding address stored in the monitor. 138 size_t ForwardingAddress() const; 139 140 // Default constructor with no lock ownership. 141 LockWord(); 142 143 // Constructor a lock word for inflation to use a Monitor. 144 explicit LockWord(Monitor* mon); 145 146 bool operator==(const LockWord& rhs) const { 147 return GetValue() == rhs.GetValue(); 148 } 149 150 // Return the hash code stored in the lock word, must be kHashCode state. 151 int32_t GetHashCode() const; 152 GetValue()153 uint32_t GetValue() const { 154 return value_; 155 } 156 157 private: LockWord(uint32_t val)158 explicit LockWord(uint32_t val) : value_(val) {} 159 160 // Only Object should be converting LockWords to/from uints. 161 friend class mirror::Object; 162 163 // The encoded value holding all the state. 164 uint32_t value_; 165 }; 166 std::ostream& operator<<(std::ostream& os, const LockWord::LockState& code); 167 168 } // namespace art 169 170 171 #endif // ART_RUNTIME_LOCK_WORD_H_ 172