/*
* 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/bit_utils.h"
#include "base/logging.h"
#include "read_barrier.h"
namespace art {
namespace mirror {
class Object;
} // namespace mirror
class Monitor;
/* The lock value itself as stored in mirror::Object::monitor_. The two most significant bits of
* the state. The four possible states are fat locked, thin/unlocked, hash code, and forwarding
* address. When the lock word is in the "thin" state and its bits are formatted as follows:
*
* |33|22|222222221111|1111110000000000|
* |10|98|765432109876|5432109876543210|
* |00|rb| lock count |thread id owner |
*
* When the lock word is in the "fat" state and its bits are formatted as follows:
*
* |33|22|2222222211111111110000000000|
* |10|98|7654321098765432109876543210|
* |01|rb| MonitorId |
*
* When the lock word is in hash state and its bits are formatted as follows:
*
* |33|22|2222222211111111110000000000|
* |10|98|7654321098765432109876543210|
* |10|rb| HashCode |
*
* When the lock word is in fowarding address state and its bits are formatted as follows:
*
* |33|22|2222222211111111110000000000|
* |10|98|7654321098765432109876543210|
* |11| ForwardingAddress |
*
* The rb bits store the read barrier state.
*/
class LockWord {
public:
enum SizeShiftsAndMasks { // private marker to avoid generate-operator-out.py from processing.
// Number of bits to encode the state, currently just fat or thin/unlocked or hash code.
kStateSize = 2,
kReadBarrierStateSize = 2,
// Number of bits to encode the thin lock owner.
kThinLockOwnerSize = 16,
// Remaining bits are the recursive lock count.
kThinLockCountSize = 32 - kThinLockOwnerSize - kStateSize - kReadBarrierStateSize,
// Thin lock bits. Owner in lowest bits.
kThinLockOwnerShift = 0,
kThinLockOwnerMask = (1 << kThinLockOwnerSize) - 1,
kThinLockMaxOwner = kThinLockOwnerMask,
// Count in higher bits.
kThinLockCountShift = kThinLockOwnerSize + kThinLockOwnerShift,
kThinLockCountMask = (1 << kThinLockCountSize) - 1,
kThinLockMaxCount = kThinLockCountMask,
kThinLockCountOne = 1 << kThinLockCountShift, // == 65536 (0x10000)
// State in the highest bits.
kStateShift = kReadBarrierStateSize + kThinLockCountSize + kThinLockCountShift,
kStateMask = (1 << kStateSize) - 1,
kStateMaskShifted = kStateMask << kStateShift,
kStateThinOrUnlocked = 0,
kStateFat = 1,
kStateHash = 2,
kStateForwardingAddress = 3,
kReadBarrierStateShift = kThinLockCountSize + kThinLockCountShift,
kReadBarrierStateMask = (1 << kReadBarrierStateSize) - 1,
kReadBarrierStateMaskShifted = kReadBarrierStateMask << kReadBarrierStateShift,
kReadBarrierStateMaskShiftedToggled = ~kReadBarrierStateMaskShifted,
// When the state is kHashCode, the non-state bits hold the hashcode.
// Note Object.hashCode() has the hash code layout hardcoded.
kHashShift = 0,
kHashSize = 32 - kStateSize - kReadBarrierStateSize,
kHashMask = (1 << kHashSize) - 1,
kMaxHash = kHashMask,
kMonitorIdShift = kHashShift,
kMonitorIdSize = kHashSize,
kMonitorIdMask = kHashMask,
kMonitorIdAlignmentShift = 32 - kMonitorIdSize,
kMonitorIdAlignment = 1 << kMonitorIdAlignmentShift,
kMaxMonitorId = kMaxHash
};
static LockWord FromThinLockId(uint32_t thread_id, uint32_t count, uint32_t rb_state) {
CHECK_LE(thread_id, static_cast<uint32_t>(kThinLockMaxOwner));
CHECK_LE(count, static_cast<uint32_t>(kThinLockMaxCount));
DCHECK_EQ(rb_state & ~kReadBarrierStateMask, 0U);
return LockWord((thread_id << kThinLockOwnerShift) | (count << kThinLockCountShift) |
(rb_state << kReadBarrierStateShift) |
(kStateThinOrUnlocked << kStateShift));
}
static LockWord FromForwardingAddress(size_t target) {
DCHECK(IsAligned < 1 << kStateSize>(target));
return LockWord((target >> kStateSize) | (kStateForwardingAddress << kStateShift));
}
static LockWord FromHashCode(uint32_t hash_code, uint32_t rb_state) {
CHECK_LE(hash_code, static_cast<uint32_t>(kMaxHash));
DCHECK_EQ(rb_state & ~kReadBarrierStateMask, 0U);
return LockWord((hash_code << kHashShift) |
(rb_state << kReadBarrierStateShift) |
(kStateHash << kStateShift));
}
static LockWord FromDefault(uint32_t rb_state) {
DCHECK_EQ(rb_state & ~kReadBarrierStateMask, 0U);
return LockWord(rb_state << kReadBarrierStateShift);
}
static bool IsDefault(LockWord lw) {
return LockWord().GetValue() == lw.GetValue();
}
static LockWord Default() {
return LockWord();
}
enum LockState {
kUnlocked, // No lock owners.
kThinLocked, // Single uncontended owner.
kFatLocked, // See associated monitor.
kHashCode, // Lock word contains an identity hash.
kForwardingAddress, // Lock word contains the forwarding address of an object.
};
LockState GetState() const {
CheckReadBarrierState();
if ((!kUseReadBarrier && UNLIKELY(value_ == 0)) ||
(kUseReadBarrier && UNLIKELY((value_ & kReadBarrierStateMaskShiftedToggled) == 0))) {
return kUnlocked;
} else {
uint32_t internal_state = (value_ >> kStateShift) & kStateMask;
switch (internal_state) {
case kStateThinOrUnlocked:
return kThinLocked;
case kStateHash:
return kHashCode;
case kStateForwardingAddress:
return kForwardingAddress;
default:
DCHECK_EQ(internal_state, static_cast<uint32_t>(kStateFat));
return kFatLocked;
}
}
}
uint32_t ReadBarrierState() const {
return (value_ >> kReadBarrierStateShift) & kReadBarrierStateMask;
}
void SetReadBarrierState(uint32_t rb_state) {
DCHECK_EQ(rb_state & ~kReadBarrierStateMask, 0U);
DCHECK_NE(static_cast<uint32_t>(GetState()), static_cast<uint32_t>(kForwardingAddress));
// Clear and or the bits.
value_ &= ~(kReadBarrierStateMask << kReadBarrierStateShift);
value_ |= (rb_state & kReadBarrierStateMask) << kReadBarrierStateShift;
}
// 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;
// Return the forwarding address stored in the monitor.
size_t ForwardingAddress() const;
// Constructor a lock word for inflation to use a Monitor.
explicit LockWord(Monitor* mon, uint32_t rb_state);
// Return the hash code stored in the lock word, must be kHashCode state.
int32_t GetHashCode() const;
template <bool kIncludeReadBarrierState>
static bool Equal(LockWord lw1, LockWord lw2) {
if (kIncludeReadBarrierState) {
return lw1.GetValue() == lw2.GetValue();
}
return lw1.GetValueWithoutReadBarrierState() == lw2.GetValueWithoutReadBarrierState();
}
private:
// Default constructor with no lock ownership.
LockWord();
explicit LockWord(uint32_t val) : value_(val) {
CheckReadBarrierState();
}
// Disallow this in favor of explicit Equal() with the
// kIncludeReadBarrierState param to make clients be aware of the
// read barrier state.
bool operator==(const LockWord& rhs) = delete;
void CheckReadBarrierState() const {
if (kIsDebugBuild && ((value_ >> kStateShift) & kStateMask) != kStateForwardingAddress) {
uint32_t rb_state = ReadBarrierState();
if (!kUseReadBarrier) {
DCHECK_EQ(rb_state, 0U);
} else {
DCHECK(rb_state == ReadBarrier::white_ptr_ ||
rb_state == ReadBarrier::gray_ptr_ ||
rb_state == ReadBarrier::black_ptr_) << rb_state;
}
}
}
// Note GetValue() includes the read barrier bits and comparing (==)
// GetValue() between two lock words to compare the lock states may
// not work. Prefer Equal() or GetValueWithoutReadBarrierState().
uint32_t GetValue() const {
CheckReadBarrierState();
return value_;
}
uint32_t GetValueWithoutReadBarrierState() const {
CheckReadBarrierState();
return value_ & ~(kReadBarrierStateMask << kReadBarrierStateShift);
}
// 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_