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Yao
2024-12-20 17:49:45 +08:00
parent 86b0363ce1
commit 654d456c7d
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// Copyright 2018 The Abseil Authors.
//
// 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
//
// https://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.
#include "absl/container/internal/raw_hash_set.h"
#include <atomic>
#include <cassert>
#include <cstddef>
#include <cstdint>
#include <cstring>
#include "absl/base/attributes.h"
#include "absl/base/config.h"
#include "absl/base/dynamic_annotations.h"
#include "absl/container/internal/container_memory.h"
#include "absl/hash/hash.h"
namespace absl {
ABSL_NAMESPACE_BEGIN
namespace container_internal {
// We have space for `growth_left` before a single block of control bytes. A
// single block of empty control bytes for tables without any slots allocated.
// This enables removing a branch in the hot path of find(). In order to ensure
// that the control bytes are aligned to 16, we have 16 bytes before the control
// bytes even though growth_left only needs 8.
constexpr ctrl_t ZeroCtrlT() { return static_cast<ctrl_t>(0); }
alignas(16) ABSL_CONST_INIT ABSL_DLL const ctrl_t kEmptyGroup[32] = {
ZeroCtrlT(), ZeroCtrlT(), ZeroCtrlT(), ZeroCtrlT(),
ZeroCtrlT(), ZeroCtrlT(), ZeroCtrlT(), ZeroCtrlT(),
ZeroCtrlT(), ZeroCtrlT(), ZeroCtrlT(), ZeroCtrlT(),
ZeroCtrlT(), ZeroCtrlT(), ZeroCtrlT(), ZeroCtrlT(),
ctrl_t::kSentinel, ctrl_t::kEmpty, ctrl_t::kEmpty, ctrl_t::kEmpty,
ctrl_t::kEmpty, ctrl_t::kEmpty, ctrl_t::kEmpty, ctrl_t::kEmpty,
ctrl_t::kEmpty, ctrl_t::kEmpty, ctrl_t::kEmpty, ctrl_t::kEmpty,
ctrl_t::kEmpty, ctrl_t::kEmpty, ctrl_t::kEmpty, ctrl_t::kEmpty};
#ifdef ABSL_INTERNAL_NEED_REDUNDANT_CONSTEXPR_DECL
constexpr size_t Group::kWidth;
#endif
namespace {
// Returns "random" seed.
inline size_t RandomSeed() {
#ifdef ABSL_HAVE_THREAD_LOCAL
static thread_local size_t counter = 0;
// On Linux kernels >= 5.4 the MSAN runtime has a false-positive when
// accessing thread local storage data from loaded libraries
// (https://github.com/google/sanitizers/issues/1265), for this reason counter
// needs to be annotated as initialized.
ABSL_ANNOTATE_MEMORY_IS_INITIALIZED(&counter, sizeof(size_t));
size_t value = ++counter;
#else // ABSL_HAVE_THREAD_LOCAL
static std::atomic<size_t> counter(0);
size_t value = counter.fetch_add(1, std::memory_order_relaxed);
#endif // ABSL_HAVE_THREAD_LOCAL
return value ^ static_cast<size_t>(reinterpret_cast<uintptr_t>(&counter));
}
bool ShouldRehashForBugDetection(const ctrl_t* ctrl, size_t capacity) {
// Note: we can't use the abseil-random library because abseil-random
// depends on swisstable. We want to return true with probability
// `min(1, RehashProbabilityConstant() / capacity())`. In order to do this,
// we probe based on a random hash and see if the offset is less than
// RehashProbabilityConstant().
return probe(ctrl, capacity, absl::HashOf(RandomSeed())).offset() <
RehashProbabilityConstant();
}
} // namespace
GenerationType* EmptyGeneration() {
if (SwisstableGenerationsEnabled()) {
constexpr size_t kNumEmptyGenerations = 1024;
static constexpr GenerationType kEmptyGenerations[kNumEmptyGenerations]{};
return const_cast<GenerationType*>(
&kEmptyGenerations[RandomSeed() % kNumEmptyGenerations]);
}
return nullptr;
}
bool CommonFieldsGenerationInfoEnabled::
should_rehash_for_bug_detection_on_insert(const ctrl_t* ctrl,
size_t capacity) const {
if (reserved_growth_ == kReservedGrowthJustRanOut) return true;
if (reserved_growth_ > 0) return false;
return ShouldRehashForBugDetection(ctrl, capacity);
}
bool CommonFieldsGenerationInfoEnabled::should_rehash_for_bug_detection_on_move(
const ctrl_t* ctrl, size_t capacity) const {
return ShouldRehashForBugDetection(ctrl, capacity);
}
bool ShouldInsertBackwards(size_t hash, const ctrl_t* ctrl) {
// To avoid problems with weak hashes and single bit tests, we use % 13.
// TODO(kfm,sbenza): revisit after we do unconditional mixing
return (H1(hash, ctrl) ^ RandomSeed()) % 13 > 6;
}
void ConvertDeletedToEmptyAndFullToDeleted(ctrl_t* ctrl, size_t capacity) {
assert(ctrl[capacity] == ctrl_t::kSentinel);
assert(IsValidCapacity(capacity));
for (ctrl_t* pos = ctrl; pos < ctrl + capacity; pos += Group::kWidth) {
Group{pos}.ConvertSpecialToEmptyAndFullToDeleted(pos);
}
// Copy the cloned ctrl bytes.
std::memcpy(ctrl + capacity + 1, ctrl, NumClonedBytes());
ctrl[capacity] = ctrl_t::kSentinel;
}
// Extern template instantiation for inline function.
template FindInfo find_first_non_full(const CommonFields&, size_t);
FindInfo find_first_non_full_outofline(const CommonFields& common,
size_t hash) {
return find_first_non_full(common, hash);
}
// Returns the address of the slot just after slot assuming each slot has the
// specified size.
static inline void* NextSlot(void* slot, size_t slot_size) {
return reinterpret_cast<void*>(reinterpret_cast<uintptr_t>(slot) + slot_size);
}
// Returns the address of the slot just before slot assuming each slot has the
// specified size.
static inline void* PrevSlot(void* slot, size_t slot_size) {
return reinterpret_cast<void*>(reinterpret_cast<uintptr_t>(slot) - slot_size);
}
void DropDeletesWithoutResize(CommonFields& common,
const PolicyFunctions& policy, void* tmp_space) {
void* set = &common;
void* slot_array = common.slot_array();
const size_t capacity = common.capacity();
assert(IsValidCapacity(capacity));
assert(!is_small(capacity));
// Algorithm:
// - mark all DELETED slots as EMPTY
// - mark all FULL slots as DELETED
// - for each slot marked as DELETED
// hash = Hash(element)
// target = find_first_non_full(hash)
// if target is in the same group
// mark slot as FULL
// else if target is EMPTY
// transfer element to target
// mark slot as EMPTY
// mark target as FULL
// else if target is DELETED
// swap current element with target element
// mark target as FULL
// repeat procedure for current slot with moved from element (target)
ctrl_t* ctrl = common.control();
ConvertDeletedToEmptyAndFullToDeleted(ctrl, capacity);
auto hasher = policy.hash_slot;
auto transfer = policy.transfer;
const size_t slot_size = policy.slot_size;
size_t total_probe_length = 0;
void* slot_ptr = SlotAddress(slot_array, 0, slot_size);
for (size_t i = 0; i != capacity;
++i, slot_ptr = NextSlot(slot_ptr, slot_size)) {
assert(slot_ptr == SlotAddress(slot_array, i, slot_size));
if (!IsDeleted(ctrl[i])) continue;
const size_t hash = (*hasher)(set, slot_ptr);
const FindInfo target = find_first_non_full(common, hash);
const size_t new_i = target.offset;
total_probe_length += target.probe_length;
// Verify if the old and new i fall within the same group wrt the hash.
// If they do, we don't need to move the object as it falls already in the
// best probe we can.
const size_t probe_offset = probe(common, hash).offset();
const auto probe_index = [probe_offset, capacity](size_t pos) {
return ((pos - probe_offset) & capacity) / Group::kWidth;
};
// Element doesn't move.
if (ABSL_PREDICT_TRUE(probe_index(new_i) == probe_index(i))) {
SetCtrl(common, i, H2(hash), slot_size);
continue;
}
void* new_slot_ptr = SlotAddress(slot_array, new_i, slot_size);
if (IsEmpty(ctrl[new_i])) {
// Transfer element to the empty spot.
// SetCtrl poisons/unpoisons the slots so we have to call it at the
// right time.
SetCtrl(common, new_i, H2(hash), slot_size);
(*transfer)(set, new_slot_ptr, slot_ptr);
SetCtrl(common, i, ctrl_t::kEmpty, slot_size);
} else {
assert(IsDeleted(ctrl[new_i]));
SetCtrl(common, new_i, H2(hash), slot_size);
// Until we are done rehashing, DELETED marks previously FULL slots.
// Swap i and new_i elements.
(*transfer)(set, tmp_space, new_slot_ptr);
(*transfer)(set, new_slot_ptr, slot_ptr);
(*transfer)(set, slot_ptr, tmp_space);
// repeat the processing of the ith slot
--i;
slot_ptr = PrevSlot(slot_ptr, slot_size);
}
}
ResetGrowthLeft(common);
common.infoz().RecordRehash(total_probe_length);
}
static bool WasNeverFull(CommonFields& c, size_t index) {
if (is_single_group(c.capacity())) {
return true;
}
const size_t index_before = (index - Group::kWidth) & c.capacity();
const auto empty_after = Group(c.control() + index).MaskEmpty();
const auto empty_before = Group(c.control() + index_before).MaskEmpty();
// We count how many consecutive non empties we have to the right and to the
// left of `it`. If the sum is >= kWidth then there is at least one probe
// window that might have seen a full group.
return empty_before && empty_after &&
static_cast<size_t>(empty_after.TrailingZeros()) +
empty_before.LeadingZeros() <
Group::kWidth;
}
void EraseMetaOnly(CommonFields& c, size_t index, size_t slot_size) {
assert(IsFull(c.control()[index]) && "erasing a dangling iterator");
c.decrement_size();
c.infoz().RecordErase();
if (WasNeverFull(c, index)) {
SetCtrl(c, index, ctrl_t::kEmpty, slot_size);
c.set_growth_left(c.growth_left() + 1);
return;
}
SetCtrl(c, index, ctrl_t::kDeleted, slot_size);
}
void ClearBackingArray(CommonFields& c, const PolicyFunctions& policy,
bool reuse) {
c.set_size(0);
if (reuse) {
ResetCtrl(c, policy.slot_size);
ResetGrowthLeft(c);
c.infoz().RecordStorageChanged(0, c.capacity());
} else {
// We need to record infoz before calling dealloc, which will unregister
// infoz.
c.infoz().RecordClearedReservation();
c.infoz().RecordStorageChanged(0, 0);
(*policy.dealloc)(c, policy);
c.set_control(EmptyGroup());
c.set_generation_ptr(EmptyGeneration());
c.set_slots(nullptr);
c.set_capacity(0);
}
}
void HashSetResizeHelper::GrowIntoSingleGroupShuffleControlBytes(
ctrl_t* new_ctrl, size_t new_capacity) const {
assert(is_single_group(new_capacity));
constexpr size_t kHalfWidth = Group::kWidth / 2;
assert(old_capacity_ < kHalfWidth);
const size_t half_old_capacity = old_capacity_ / 2;
// NOTE: operations are done with compile time known size = kHalfWidth.
// Compiler optimizes that into single ASM operation.
// Copy second half of bytes to the beginning.
// We potentially copy more bytes in order to have compile time known size.
// Mirrored bytes from the old_ctrl_ will also be copied.
// In case of old_capacity_ == 3, we will copy 1st element twice.
// Examples:
// old_ctrl = 0S0EEEEEEE...
// new_ctrl = S0EEEEEEEE...
//
// old_ctrl = 01S01EEEEE...
// new_ctrl = 1S01EEEEEE...
//
// old_ctrl = 0123456S0123456EE...
// new_ctrl = 456S0123?????????...
std::memcpy(new_ctrl, old_ctrl_ + half_old_capacity + 1, kHalfWidth);
// Clean up copied kSentinel from old_ctrl.
new_ctrl[half_old_capacity] = ctrl_t::kEmpty;
// Clean up damaged or uninitialized bytes.
// Clean bytes after the intended size of the copy.
// Example:
// new_ctrl = 1E01EEEEEEE????
// *new_ctrl= 1E0EEEEEEEE????
// position /
std::memset(new_ctrl + old_capacity_ + 1, static_cast<int8_t>(ctrl_t::kEmpty),
kHalfWidth);
// Clean non-mirrored bytes that are not initialized.
// For small old_capacity that may be inside of mirrored bytes zone.
// Examples:
// new_ctrl = 1E0EEEEEEEE??????????....
// *new_ctrl= 1E0EEEEEEEEEEEEE?????....
// position /
//
// new_ctrl = 456E0123???????????...
// *new_ctrl= 456E0123EEEEEEEE???...
// position /
std::memset(new_ctrl + kHalfWidth, static_cast<int8_t>(ctrl_t::kEmpty),
kHalfWidth);
// Clean last mirrored bytes that are not initialized
// and will not be overwritten by mirroring.
// Examples:
// new_ctrl = 1E0EEEEEEEEEEEEE????????
// *new_ctrl= 1E0EEEEEEEEEEEEEEEEEEEEE
// position S /
//
// new_ctrl = 456E0123EEEEEEEE???????????????
// *new_ctrl= 456E0123EEEEEEEE???????EEEEEEEE
// position S /
std::memset(new_ctrl + new_capacity + kHalfWidth,
static_cast<int8_t>(ctrl_t::kEmpty), kHalfWidth);
// Create mirrored bytes. old_capacity_ < kHalfWidth
// Example:
// new_ctrl = 456E0123EEEEEEEE???????EEEEEEEE
// *new_ctrl= 456E0123EEEEEEEE456E0123EEEEEEE
// position S/
ctrl_t g[kHalfWidth];
std::memcpy(g, new_ctrl, kHalfWidth);
std::memcpy(new_ctrl + new_capacity + 1, g, kHalfWidth);
// Finally set sentinel to its place.
new_ctrl[new_capacity] = ctrl_t::kSentinel;
}
void HashSetResizeHelper::GrowIntoSingleGroupShuffleTransferableSlots(
void* old_slots, void* new_slots, size_t slot_size) const {
assert(old_capacity_ > 0);
const size_t half_old_capacity = old_capacity_ / 2;
SanitizerUnpoisonMemoryRegion(old_slots, slot_size * old_capacity_);
std::memcpy(new_slots,
SlotAddress(old_slots, half_old_capacity + 1, slot_size),
slot_size * half_old_capacity);
std::memcpy(SlotAddress(new_slots, half_old_capacity + 1, slot_size),
old_slots, slot_size * (half_old_capacity + 1));
}
void HashSetResizeHelper::GrowSizeIntoSingleGroupTransferable(
CommonFields& c, void* old_slots, size_t slot_size) {
assert(old_capacity_ < Group::kWidth / 2);
assert(is_single_group(c.capacity()));
assert(IsGrowingIntoSingleGroupApplicable(old_capacity_, c.capacity()));
GrowIntoSingleGroupShuffleControlBytes(c.control(), c.capacity());
GrowIntoSingleGroupShuffleTransferableSlots(old_slots, c.slot_array(),
slot_size);
// We poison since GrowIntoSingleGroupShuffleTransferableSlots
// may leave empty slots unpoisoned.
PoisonSingleGroupEmptySlots(c, slot_size);
}
} // namespace container_internal
ABSL_NAMESPACE_END
} // namespace absl