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/*
* Copyright (C) 2011 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
#ifndef ART_RUNTIME_LOCK_WORD_H_
#define ART_RUNTIME_LOCK_WORD_H_
#include <iosfwd>
#include <stdint.h>
#include "base/logging.h"
namespace art {
namespace mirror {
class Object;
} // namespace mirror
class Monitor;
/* The lock value itself as stored in mirror::Object::monitor_. The MSB of the lock encodes its
* state. When cleared, the lock is in the "thin" state and its bits are formatted as follows:
*
* |3|32222222222111|11111110000000000|
* |1|09876543210987|65432109876543210|
* |0| lock count | thread id |
*
* When set, the lock is in the "fat" state and its bits are formatted as follows:
*
* |3|3222222222211111111110000000000|
* |1|0987654321098765432109876543210|
* |1| Monitor* >> 1 |
*/
class LockWord {
public:
enum {
// Number of bits to encode the state, currently just fat or thin/unlocked.
kStateSize = 1,
// Number of bits to encode the thin lock owner.
kThinLockOwnerSize = 16,
// Remaining bits are the recursive lock count.
kThinLockCountSize = 32 - kThinLockOwnerSize - kStateSize,
// Thin lock bits. Owner in lowest bits.
kThinLockOwnerShift = 0,
kThinLockOwnerMask = (1 << kThinLockOwnerSize) - 1,
// Count in higher bits.
kThinLockCountShift = kThinLockOwnerSize + kThinLockOwnerShift,
kThinLockCountMask = (1 << kThinLockCountShift) - 1,
kThinLockMaxCount = kThinLockCountMask,
// State in the highest bits.
kStateShift = kThinLockCountSize + kThinLockCountShift,
kStateMask = (1 << kStateSize) - 1,
kStateThinOrUnlocked = 0,
kStateFat = 1,
};
static LockWord FromThinLockId(uint32_t thread_id, uint32_t count) {
CHECK_LE(thread_id, static_cast<uint32_t>(kThinLockOwnerMask));
return LockWord((thread_id << kThinLockOwnerShift) | (count << kThinLockCountShift));
}
enum LockState {
kUnlocked, // No lock owners.
kThinLocked, // Single uncontended owner.
kFatLocked // See associated monitor.
};
LockState GetState() const {
if (value_ == 0) {
return kUnlocked;
} else if (((value_ >> kStateShift) & kStateMask) == kStateThinOrUnlocked) {
return kThinLocked;
} else {
return kFatLocked;
}
}
// Return the owner thin lock thread id.
uint32_t ThinLockOwner() const;
// Return the number of times a lock value has been locked.
uint32_t ThinLockCount() const;
// Return the Monitor encoded in a fat lock.
Monitor* FatLockMonitor() const;
// Default constructor with no lock ownership.
LockWord();
// Constructor a lock word for inflation to use a Monitor.
explicit LockWord(Monitor* mon);
bool operator==(const LockWord& rhs) {
return GetValue() == rhs.GetValue();
}
private:
explicit LockWord(uint32_t val) : value_(val) {}
uint32_t GetValue() const {
return value_;
}
// Only Object should be converting LockWords to/from uints.
friend class mirror::Object;
// The encoded value holding all the state.
uint32_t value_;
};
std::ostream& operator<<(std::ostream& os, const LockWord::LockState& code);
} // namespace art
#endif // ART_RUNTIME_LOCK_WORD_H_
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