lock_word.h revision 8d82de5d7b04b8f43e7d2bb7ee8a66b0c7e71e1b 
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
26namespace art {
27namespace mirror {
28  class Object;
29}  // namespace mirror
30
31class 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 */
53class 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
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
91  static LockWord FromForwardingAddress(size_t target) {
92    DCHECK(IsAligned < 1 << kStateSize>(target));
93    return LockWord((target >> kStateSize) | (kStateForwardingAddress << kStateShift));
94  }
95
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
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
153  uint32_t GetValue() const {
154    return value_;
155  }
156
157 private:
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};
166std::ostream& operator<<(std::ostream& os, const LockWord::LockState& code);
167
168}  // namespace art
169
170
171#endif  // ART_RUNTIME_LOCK_WORD_H_
172