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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 <cstdint>
#include <iosfwd>
#include <android-base/logging.h>
#include "base/bit_utils.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
* encode 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|2|2|222222221111|1111110000000000|
* |10|9|8|765432109876|5432109876543210|
* |00|m|r| lock count |thread id owner |
*
* The lock count is zero, but the owner is nonzero for a simply held lock.
* When the lock word is in the "fat" state and its bits are formatted as follows:
*
* |33|2|2|2222222211111111110000000000|
* |10|9|8|7654321098765432109876543210|
* |01|m|r| MonitorId |
*
* When the lock word is in hash state and its bits are formatted as follows:
*
* |33|2|2|2222222211111111110000000000|
* |10|9|8|7654321098765432109876543210|
* |10|m|r| HashCode |
*
* When the lock word is in forwarding address state and its bits are formatted as follows:
*
* |33|2|22222222211111111110000000000|
* |10|9|87654321098765432109876543210|
* |11|0| ForwardingAddress |
*
* The `r` bit stores the read barrier state.
* The `m` bit stores the mark bit state.
*/
class LockWord {
public:
enum SizeShiftsAndMasks : uint32_t { // 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 = 1,
kMarkBitStateSize = 1,
// Number of bits to encode the thin lock owner.
kThinLockOwnerSize = 16,
// Remaining bits are the recursive lock count. Zero means it is locked exactly once
// and not recursively.
kThinLockCountSize = 32 - kThinLockOwnerSize - kStateSize - kReadBarrierStateSize -
kMarkBitStateSize,
// Thin lock bits. Owner in lowest bits.
kThinLockOwnerShift = 0,
kThinLockOwnerMask = (1 << kThinLockOwnerSize) - 1,
kThinLockOwnerMaskShifted = kThinLockOwnerMask << kThinLockOwnerShift,
kThinLockMaxOwner = kThinLockOwnerMask,
// Count in higher bits.
kThinLockCountShift = kThinLockOwnerSize + kThinLockOwnerShift,
kThinLockCountMask = (1 << kThinLockCountSize) - 1,
kThinLockMaxCount = kThinLockCountMask,
kThinLockCountOne = 1 << kThinLockCountShift, // == 65536 (0x10000)
kThinLockCountMaskShifted = kThinLockCountMask << kThinLockCountShift,
// State in the highest bits.
kStateShift = kReadBarrierStateSize + kThinLockCountSize + kThinLockCountShift +
kMarkBitStateSize,
kStateMask = (1 << kStateSize) - 1,
kStateMaskShifted = kStateMask << kStateShift,
kStateThinOrUnlocked = 0,
kStateFat = 1,
kStateHash = 2,
kStateForwardingAddress = 3,
kStateForwardingAddressShifted = kStateForwardingAddress << kStateShift,
kStateForwardingAddressOverflow = (1 + kStateMask - kStateForwardingAddress) << kStateShift,
// Read barrier bit.
kReadBarrierStateShift = kThinLockCountSize + kThinLockCountShift,
kReadBarrierStateMask = (1 << kReadBarrierStateSize) - 1,
kReadBarrierStateMaskShifted = kReadBarrierStateMask << kReadBarrierStateShift,
kReadBarrierStateMaskShiftedToggled = ~kReadBarrierStateMaskShifted,
// Mark bit.
kMarkBitStateShift = kReadBarrierStateSize + kReadBarrierStateShift,
kMarkBitStateMask = (1 << kMarkBitStateSize) - 1,
kMarkBitStateMaskShifted = kMarkBitStateMask << kMarkBitStateShift,
kMarkBitStateMaskShiftedToggled = ~kMarkBitStateMaskShifted,
// GC state is mark bit and read barrier state.
kGCStateSize = kReadBarrierStateSize + kMarkBitStateSize,
kGCStateShift = kReadBarrierStateShift,
kGCStateMaskShifted = kReadBarrierStateMaskShifted | kMarkBitStateMaskShifted,
kGCStateMaskShiftedToggled = ~kGCStateMaskShifted,
// 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 - kMarkBitStateSize,
kHashMask = (1 << kHashSize) - 1,
kMaxHash = kHashMask,
// Forwarding address shift.
kForwardingAddressShift = kObjectAlignmentShift,
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 gc_state) {
CHECK_LE(thread_id, static_cast<uint32_t>(kThinLockMaxOwner));
CHECK_LE(count, static_cast<uint32_t>(kThinLockMaxCount));
// DCHECK_EQ(gc_bits & kGCStateMaskToggled, 0U);
return LockWord((thread_id << kThinLockOwnerShift) |
(count << kThinLockCountShift) |
(gc_state << kGCStateShift) |
(kStateThinOrUnlocked << kStateShift));
}
static LockWord FromForwardingAddress(size_t target) {
DCHECK_ALIGNED(target, (1 << kStateSize));
return LockWord((target >> kForwardingAddressShift) | kStateForwardingAddressShifted);
}
static LockWord FromHashCode(uint32_t hash_code, uint32_t gc_state) {
CHECK_LE(hash_code, static_cast<uint32_t>(kMaxHash));
// DCHECK_EQ(gc_bits & kGCStateMaskToggled, 0U);
return LockWord((hash_code << kHashShift) |
(gc_state << kGCStateShift) |
(kStateHash << kStateShift));
}
static LockWord FromDefault(uint32_t gc_state) {
return LockWord(gc_state << kGCStateShift);
}
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_ & kGCStateMaskShiftedToggled) == 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;
}
uint32_t GCState() const {
return (value_ & kGCStateMaskShifted) >> kGCStateShift;
}
void SetReadBarrierState(uint32_t rb_state) {
DCHECK_EQ(rb_state & ~kReadBarrierStateMask, 0U);
DCHECK(rb_state == ReadBarrier::NonGrayState() ||
rb_state == ReadBarrier::GrayState()) << rb_state;
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;
}
uint32_t MarkBitState() const {
return (value_ >> kMarkBitStateShift) & kMarkBitStateMask;
}
void SetMarkBitState(uint32_t mark_bit) {
DCHECK_EQ(mark_bit & ~kMarkBitStateMask, 0U);
DCHECK_NE(static_cast<uint32_t>(GetState()), static_cast<uint32_t>(kForwardingAddress));
// Clear and or the bits.
value_ &= kMarkBitStateMaskShiftedToggled;
value_ |= mark_bit << kMarkBitStateShift;
}
// Return the owner thin lock thread id.
uint32_t ThinLockOwner() const;
// Return the number of times a lock value has been re-locked. Only valid in thin-locked state.
// If the lock is held only once the return value is zero.
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.
LockWord(Monitor* mon, uint32_t gc_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.GetValueWithoutGCState() == lw2.GetValueWithoutGCState();
}
void Dump(std::ostream& os) {
os << "LockWord:" << std::hex << value_;
}
private:
// Default constructor with no lock ownership.
LockWord();
explicit LockWord(uint32_t val) : value_(val) {
// Make sure adding the overflow causes an overflow.
constexpr uint64_t overflow = static_cast<uint64_t>(kStateForwardingAddressShifted) +
static_cast<uint64_t>(kStateForwardingAddressOverflow);
constexpr bool is_larger = overflow > static_cast<uint64_t>(0xFFFFFFFF);
static_assert(is_larger, "should have overflowed");
static_assert(
(~kStateForwardingAddress & kStateMask) == 0,
"READ_BARRIER_MARK_REG relies on the forwarding address state being only one bits");
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::NonGrayState() ||
rb_state == ReadBarrier::GrayState()) << 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 GetValueWithoutGCState() const {
CheckReadBarrierState();
return value_ & kGCStateMaskShiftedToggled;
}
// 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, LockWord::LockState code);
} // namespace art
#endif // ART_RUNTIME_LOCK_WORD_H_