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abseil-cpp
Commit 1980d7b9 by Evan Brown Committed by Copybara-Service
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Do hashtablez sampling on the first insertion into an empty SOO hashtable. 

When sampling triggers, we skip SOO and allocate a backing array. We must do this because the HashtablezInfoHandle is part of the heap allocation (along with the control bytes and slots). By default, we sample 1 in ~1024 hashtables when sampling is enabled. This will impact performance because (a) we won't benefit from SOO so we would have worse data locality (more cache/TLB misses), and (b) the backing array capacity will be 3 instead of 1 so (b.1) we skip the rehash after the second insertion and (b.2) we potentially waste up to two slots worth of memory.

We also add an soo_capacity field to HashtablezInfo to allow for distinguishing which sampled tables may otherwise have been SOO - this will allow us to know approximately what fraction of tables are in SOO mode.

PiperOrigin-RevId: 617252334
Change-Id: Ib48b7a4870bd74ea3ba923ed8f350a3b75dbb7d3
parent 43c36ffa
Showing with 348 additions and 92 deletions
absl/container/BUILD.bazel
......@@ -701,8 +701,10 @@ cc_test(
"//absl/base:config",
"//absl/base:core_headers",
"//absl/base:prefetch",
"//absl/functional:function_ref",
"//absl/hash",
"//absl/log",
"//absl/log:check",
"//absl/memory",
"//absl/meta:type_traits",
"//absl/strings",
......
absl/container/CMakeLists.txt
......@@ -753,11 +753,13 @@ absl_cc_test(
${ABSL_TEST_COPTS}
DEPS
absl::base
absl::check
absl::config
absl::container_memory
absl::core_headers
absl::flat_hash_map
absl::flat_hash_set
absl::function_ref
absl::hash
absl::hash_function_defaults
absl::hash_policy_testing
......
absl/container/internal/hashtablez_sampler.cc
......@@ -18,13 +18,18 @@
#include <atomic>
#include <cassert>
#include <cmath>
#include <cstddef>
#include <cstdint>
#include <functional>
#include <limits>
#include "absl/base/attributes.h"
#include "absl/base/config.h"
#include "absl/base/internal/per_thread_tls.h"
#include "absl/base/internal/raw_logging.h"
#include "absl/base/macros.h"
#include "absl/base/no_destructor.h"
#include "absl/base/optimization.h"
#include "absl/debugging/stacktrace.h"
#include "absl/memory/memory.h"
#include "absl/profiling/internal/exponential_biased.h"
......@@ -73,7 +78,8 @@ HashtablezInfo::HashtablezInfo() = default;
HashtablezInfo::~HashtablezInfo() = default;
void HashtablezInfo::PrepareForSampling(int64_t stride,
size_t inline_element_size_value) {
size_t inline_element_size_value,
uint16_t soo_capacity_value) {
capacity.store(0, std::memory_order_relaxed);
size.store(0, std::memory_order_relaxed);
num_erases.store(0, std::memory_order_relaxed);
......@@ -93,6 +99,7 @@ void HashtablezInfo::PrepareForSampling(int64_t stride,
depth = absl::GetStackTrace(stack, HashtablezInfo::kMaxStackDepth,
/* skip_count= */ 0);
inline_element_size = inline_element_size_value;
soo_capacity = soo_capacity_value;
}
static bool ShouldForceSampling() {
......@@ -116,12 +123,12 @@ static bool ShouldForceSampling() {
}
HashtablezInfo* SampleSlow(SamplingState& next_sample,
size_t inline_element_size) {
size_t inline_element_size, uint16_t soo_capacity) {
if (ABSL_PREDICT_FALSE(ShouldForceSampling())) {
next_sample.next_sample = 1;
const int64_t old_stride = exchange(next_sample.sample_stride, 1);
HashtablezInfo* result =
GlobalHashtablezSampler().Register(old_stride, inline_element_size);
HashtablezInfo* result = GlobalHashtablezSampler().Register(
old_stride, inline_element_size, soo_capacity);
return result;
}
......@@ -151,10 +158,11 @@ HashtablezInfo* SampleSlow(SamplingState& next_sample,
// that case.
if (first) {
if (ABSL_PREDICT_TRUE(--next_sample.next_sample > 0)) return nullptr;
return SampleSlow(next_sample, inline_element_size);
return SampleSlow(next_sample, inline_element_size, soo_capacity);
}
return GlobalHashtablezSampler().Register(old_stride, inline_element_size);
return GlobalHashtablezSampler().Register(old_stride, inline_element_size,
soo_capacity);
#endif
}
......
absl/container/internal/hashtablez_sampler.h
......@@ -40,15 +40,20 @@
#define ABSL_CONTAINER_INTERNAL_HASHTABLEZ_SAMPLER_H_
#include <atomic>
#include <cstddef>
#include <cstdint>
#include <functional>
#include <memory>
#include <vector>
#include "absl/base/attributes.h"
#include "absl/base/config.h"
#include "absl/base/internal/per_thread_tls.h"
#include "absl/base/optimization.h"
#include "absl/base/thread_annotations.h"
#include "absl/profiling/internal/sample_recorder.h"
#include "absl/synchronization/mutex.h"
#include "absl/time/time.h"
#include "absl/utility/utility.h"
namespace absl {
......@@ -67,7 +72,8 @@ struct HashtablezInfo : public profiling_internal::Sample<HashtablezInfo> {
// Puts the object into a clean state, fills in the logically `const` members,
// blocking for any readers that are currently sampling the object.
void PrepareForSampling(int64_t stride, size_t inline_element_size_value)
void PrepareForSampling(int64_t stride, size_t inline_element_size_value,
uint16_t soo_capacity_value)
ABSL_EXCLUSIVE_LOCKS_REQUIRED(init_mu);
// These fields are mutated by the various Record* APIs and need to be
......@@ -91,8 +97,13 @@ struct HashtablezInfo : public profiling_internal::Sample<HashtablezInfo> {
static constexpr int kMaxStackDepth = 64;
absl::Time create_time;
int32_t depth;
// The SOO capacity for this table in elements (not bytes). Note that sampled
// tables are never SOO because we need to store the infoz handle on the heap.
// Tables that would be SOO if not sampled should have: soo_capacity > 0 &&
// size <= soo_capacity && max_reserve <= soo_capacity.
uint16_t soo_capacity;
void* stack[kMaxStackDepth];
size_t inline_element_size; // How big is the slot?
size_t inline_element_size; // How big is the slot in bytes?
};
void RecordRehashSlow(HashtablezInfo* info, size_t total_probe_length);
......@@ -117,7 +128,7 @@ struct SamplingState {
};
HashtablezInfo* SampleSlow(SamplingState& next_sample,
size_t inline_element_size);
size_t inline_element_size, uint16_t soo_capacity);
void UnsampleSlow(HashtablezInfo* info);
#if defined(ABSL_INTERNAL_HASHTABLEZ_SAMPLE)
......@@ -204,16 +215,16 @@ class HashtablezInfoHandle {
extern ABSL_PER_THREAD_TLS_KEYWORD SamplingState global_next_sample;
#endif // defined(ABSL_INTERNAL_HASHTABLEZ_SAMPLE)
// Returns an RAII sampling handle that manages registration and unregistation
// with the global sampler.
// Returns a sampling handle.
inline HashtablezInfoHandle Sample(
size_t inline_element_size ABSL_ATTRIBUTE_UNUSED) {
ABSL_ATTRIBUTE_UNUSED size_t inline_element_size,
ABSL_ATTRIBUTE_UNUSED uint16_t soo_capacity) {
#if defined(ABSL_INTERNAL_HASHTABLEZ_SAMPLE)
if (ABSL_PREDICT_TRUE(--global_next_sample.next_sample > 0)) {
return HashtablezInfoHandle(nullptr);
}
return HashtablezInfoHandle(
SampleSlow(global_next_sample, inline_element_size));
SampleSlow(global_next_sample, inline_element_size, soo_capacity));
#else
return HashtablezInfoHandle(nullptr);
#endif // !ABSL_PER_THREAD_TLS
......
absl/container/internal/hashtablez_sampler_test.cc
......@@ -15,8 +15,12 @@
#include "absl/container/internal/hashtablez_sampler.h"
#include <atomic>
#include <cassert>
#include <cstddef>
#include <cstdint>
#include <limits>
#include <random>
#include <vector>
#include "gmock/gmock.h"
#include "gtest/gtest.h"
......@@ -67,7 +71,7 @@ std::vector<size_t> GetSizes(HashtablezSampler* s) {
HashtablezInfo* Register(HashtablezSampler* s, size_t size) {
const int64_t test_stride = 123;
const size_t test_element_size = 17;
auto* info = s->Register(test_stride, test_element_size);
auto* info = s->Register(test_stride, test_element_size, /*soo_capacity=*/0);
assert(info != nullptr);
info->size.store(size);
return info;
......@@ -79,7 +83,8 @@ TEST(HashtablezInfoTest, PrepareForSampling) {
const size_t test_element_size = 17;
HashtablezInfo info;
absl::MutexLock l(&info.init_mu);
info.PrepareForSampling(test_stride, test_element_size);
info.PrepareForSampling(test_stride, test_element_size,
/*soo_capacity_value=*/1);
EXPECT_EQ(info.capacity.load(), 0);
EXPECT_EQ(info.size.load(), 0);
......@@ -94,6 +99,7 @@ TEST(HashtablezInfoTest, PrepareForSampling) {
EXPECT_GE(info.create_time, test_start);
EXPECT_EQ(info.weight, test_stride);
EXPECT_EQ(info.inline_element_size, test_element_size);
EXPECT_EQ(info.soo_capacity, 1);
info.capacity.store(1, std::memory_order_relaxed);
info.size.store(1, std::memory_order_relaxed);
......@@ -106,7 +112,8 @@ TEST(HashtablezInfoTest, PrepareForSampling) {
info.max_reserve.store(1, std::memory_order_relaxed);
info.create_time = test_start - absl::Hours(20);
info.PrepareForSampling(test_stride * 2, test_element_size);
info.PrepareForSampling(test_stride * 2, test_element_size,
/*soo_capacity_value=*/0);
EXPECT_EQ(info.capacity.load(), 0);
EXPECT_EQ(info.size.load(), 0);
EXPECT_EQ(info.num_erases.load(), 0);
......@@ -120,6 +127,7 @@ TEST(HashtablezInfoTest, PrepareForSampling) {
EXPECT_EQ(info.weight, 2 * test_stride);
EXPECT_EQ(info.inline_element_size, test_element_size);
EXPECT_GE(info.create_time, test_start);
EXPECT_EQ(info.soo_capacity, 0);
}
TEST(HashtablezInfoTest, RecordStorageChanged) {
......@@ -127,7 +135,8 @@ TEST(HashtablezInfoTest, RecordStorageChanged) {
absl::MutexLock l(&info.init_mu);
const int64_t test_stride = 21;
const size_t test_element_size = 19;
info.PrepareForSampling(test_stride, test_element_size);
info.PrepareForSampling(test_stride, test_element_size,
/*soo_capacity_value=*/0);
RecordStorageChangedSlow(&info, 17, 47);
EXPECT_EQ(info.size.load(), 17);
EXPECT_EQ(info.capacity.load(), 47);
......@@ -141,7 +150,8 @@ TEST(HashtablezInfoTest, RecordInsert) {
absl::MutexLock l(&info.init_mu);
const int64_t test_stride = 25;
const size_t test_element_size = 23;
info.PrepareForSampling(test_stride, test_element_size);
info.PrepareForSampling(test_stride, test_element_size,
/*soo_capacity_value=*/0);
EXPECT_EQ(info.max_probe_length.load(), 0);
RecordInsertSlow(&info, 0x0000FF00, 6 * kProbeLength);
EXPECT_EQ(info.max_probe_length.load(), 6);
......@@ -165,7 +175,8 @@ TEST(HashtablezInfoTest, RecordErase) {
const size_t test_element_size = 29;
HashtablezInfo info;
absl::MutexLock l(&info.init_mu);
info.PrepareForSampling(test_stride, test_element_size);
info.PrepareForSampling(test_stride, test_element_size,
/*soo_capacity_value=*/1);
EXPECT_EQ(info.num_erases.load(), 0);
EXPECT_EQ(info.size.load(), 0);
RecordInsertSlow(&info, 0x0000FF00, 6 * kProbeLength);
......@@ -174,6 +185,7 @@ TEST(HashtablezInfoTest, RecordErase) {
EXPECT_EQ(info.size.load(), 0);
EXPECT_EQ(info.num_erases.load(), 1);
EXPECT_EQ(info.inline_element_size, test_element_size);
EXPECT_EQ(info.soo_capacity, 1);
}
TEST(HashtablezInfoTest, RecordRehash) {
......@@ -181,7 +193,8 @@ TEST(HashtablezInfoTest, RecordRehash) {
const size_t test_element_size = 31;
HashtablezInfo info;
absl::MutexLock l(&info.init_mu);
info.PrepareForSampling(test_stride, test_element_size);
info.PrepareForSampling(test_stride, test_element_size,
/*soo_capacity_value=*/0);
RecordInsertSlow(&info, 0x1, 0);
RecordInsertSlow(&info, 0x2, kProbeLength);
RecordInsertSlow(&info, 0x4, kProbeLength);
......@@ -201,6 +214,7 @@ TEST(HashtablezInfoTest, RecordRehash) {
EXPECT_EQ(info.num_erases.load(), 0);
EXPECT_EQ(info.num_rehashes.load(), 1);
EXPECT_EQ(info.inline_element_size, test_element_size);
EXPECT_EQ(info.soo_capacity, 0);
}
TEST(HashtablezInfoTest, RecordReservation) {
......@@ -208,7 +222,8 @@ TEST(HashtablezInfoTest, RecordReservation) {
absl::MutexLock l(&info.init_mu);
const int64_t test_stride = 35;
const size_t test_element_size = 33;
info.PrepareForSampling(test_stride, test_element_size);
info.PrepareForSampling(test_stride, test_element_size,
/*soo_capacity_value=*/0);
RecordReservationSlow(&info, 3);
EXPECT_EQ(info.max_reserve.load(), 3);
......@@ -229,7 +244,8 @@ TEST(HashtablezSamplerTest, SmallSampleParameter) {
for (int i = 0; i < 1000; ++i) {
SamplingState next_sample = {0, 0};
HashtablezInfo* sample = SampleSlow(next_sample, test_element_size);
HashtablezInfo* sample = SampleSlow(next_sample, test_element_size,
/*soo_capacity=*/0);
EXPECT_GT(next_sample.next_sample, 0);
EXPECT_EQ(next_sample.next_sample, next_sample.sample_stride);
EXPECT_NE(sample, nullptr);
......@@ -244,7 +260,8 @@ TEST(HashtablezSamplerTest, LargeSampleParameter) {
for (int i = 0; i < 1000; ++i) {
SamplingState next_sample = {0, 0};
HashtablezInfo* sample = SampleSlow(next_sample, test_element_size);
HashtablezInfo* sample = SampleSlow(next_sample, test_element_size,
/*soo_capacity=*/0);
EXPECT_GT(next_sample.next_sample, 0);
EXPECT_EQ(next_sample.next_sample, next_sample.sample_stride);
EXPECT_NE(sample, nullptr);
......@@ -260,7 +277,8 @@ TEST(HashtablezSamplerTest, Sample) {
int64_t total = 0;
double sample_rate = 0.0;
for (int i = 0; i < 1000000; ++i) {
HashtablezInfoHandle h = Sample(test_element_size);
HashtablezInfoHandle h = Sample(test_element_size,
/*soo_capacity=*/0);
++total;
if (h.IsSampled()) {
++num_sampled;
......@@ -275,7 +293,8 @@ TEST(HashtablezSamplerTest, Handle) {
auto& sampler = GlobalHashtablezSampler();
const int64_t test_stride = 41;
const size_t test_element_size = 39;
HashtablezInfoHandle h(sampler.Register(test_stride, test_element_size));
HashtablezInfoHandle h(sampler.Register(test_stride, test_element_size,
/*soo_capacity=*/0));
auto* info = HashtablezInfoHandlePeer::GetInfo(&h);
info->hashes_bitwise_and.store(0x12345678, std::memory_order_relaxed);
......@@ -358,11 +377,13 @@ TEST(HashtablezSamplerTest, MultiThreaded) {
std::vector<HashtablezInfo*> infoz;
while (!stop.HasBeenNotified()) {
if (infoz.empty()) {
infoz.push_back(sampler.Register(sampling_stride, elt_size));
infoz.push_back(sampler.Register(sampling_stride, elt_size,
/*soo_capacity=*/0));
}
switch (std::uniform_int_distribution<>(0, 2)(gen)) {
case 0: {
infoz.push_back(sampler.Register(sampling_stride, elt_size));
infoz.push_back(sampler.Register(sampling_stride, elt_size,
/*soo_capacity=*/0));
break;
}
case 1: {
......
absl/container/internal/raw_hash_set.h
......@@ -1775,17 +1775,48 @@ ABSL_ATTRIBUTE_ALWAYS_INLINE inline void IterateOverFullSlots(
}
}
template <typename CharAlloc>
constexpr bool ShouldSampleHashtablezInfo() {
// Folks with custom allocators often make unwarranted assumptions about the
// behavior of their classes vis-a-vis trivial destructability and what
// calls they will or won't make. Avoid sampling for people with custom
// allocators to get us out of this mess. This is not a hard guarantee but
// a workaround while we plan the exact guarantee we want to provide.
return std::is_same<CharAlloc, std::allocator<char>>::value;
}
template <bool kSooEnabled>
HashtablezInfoHandle SampleHashtablezInfo(size_t sizeof_slot,
size_t old_capacity, bool was_soo,
HashtablezInfoHandle forced_infoz,
CommonFields& c) {
if (forced_infoz.IsSampled()) return forced_infoz;
// In SOO, we sample on the first insertion so if this is an empty SOO case
// (e.g. when reserve is called), then we still need to sample.
if (kSooEnabled && was_soo && c.size() == 0) {
return Sample(sizeof_slot, SooCapacity());
}
// For non-SOO cases, we sample whenever the capacity is increasing from zero
// to non-zero.
if (!kSooEnabled && old_capacity == 0) {
return Sample(sizeof_slot, 0);
}
return c.infoz();
}
// Helper class to perform resize of the hash set.
//
// It contains special optimizations for small group resizes.
// See GrowIntoSingleGroupShuffleControlBytes for details.
class HashSetResizeHelper {
public:
explicit HashSetResizeHelper(CommonFields& c, bool was_soo, bool had_soo_slot)
explicit HashSetResizeHelper(CommonFields& c, bool was_soo, bool had_soo_slot,
HashtablezInfoHandle forced_infoz)
: old_capacity_(c.capacity()),
had_infoz_(c.has_infoz()),
was_soo_(was_soo),
had_soo_slot_(had_soo_slot) {}
had_soo_slot_(had_soo_slot),
forced_infoz_(forced_infoz) {}
// Optimized for small groups version of `find_first_non_full`.
// Beneficial only right after calling `raw_hash_set::resize`.
......@@ -1839,7 +1870,7 @@ class HashSetResizeHelper {
// Reads `capacity` and updates all other fields based on the result of
// the allocation.
//
// It also may do the folowing actions:
// It also may do the following actions:
// 1. initialize control bytes
// 2. initialize slots
// 3. deallocate old slots.
......@@ -1869,26 +1900,15 @@ class HashSetResizeHelper {
//
// Returns IsGrowingIntoSingleGroupApplicable result to avoid recomputation.
template <typename Alloc, size_t SizeOfSlot, bool TransferUsesMemcpy,
size_t AlignOfSlot>
bool SooEnabled, size_t AlignOfSlot>
ABSL_ATTRIBUTE_NOINLINE bool InitializeSlots(CommonFields& c, Alloc alloc,
ctrl_t soo_slot_h2) {
assert(c.capacity());
// Folks with custom allocators often make unwarranted assumptions about the
// behavior of their classes vis-a-vis trivial destructability and what
// calls they will or won't make. Avoid sampling for people with custom
// allocators to get us out of this mess. This is not a hard guarantee but
// a workaround while we plan the exact guarantee we want to provide.
const size_t sample_size =
(std::is_same<Alloc, std::allocator<char>>::value &&
(was_soo_ || old_capacity_ == 0))
? SizeOfSlot
: 0;
// TODO(b/289225379): when SOO is enabled, we should still sample on first
// insertion and if Sample is non-null, then we should force a heap
// allocation. Note that we'll also have to force capacity of 3 so that
// is_soo() still works.
HashtablezInfoHandle infoz =
sample_size > 0 ? Sample(sample_size) : c.infoz();
ShouldSampleHashtablezInfo<Alloc>()
? SampleHashtablezInfo<SooEnabled>(SizeOfSlot, old_capacity_,
was_soo_, forced_infoz_, c)
: HashtablezInfoHandle{};
const bool has_infoz = infoz.IsSampled();
RawHashSetLayout layout(c.capacity(), AlignOfSlot, has_infoz);
......@@ -1904,12 +1924,13 @@ class HashSetResizeHelper {
const bool grow_single_group =
IsGrowingIntoSingleGroupApplicable(old_capacity_, layout.capacity());
if (was_soo_ && grow_single_group) {
if (SooEnabled && was_soo_ && grow_single_group) {
InitControlBytesAfterSoo(c.control(), soo_slot_h2, layout.capacity());
if (TransferUsesMemcpy && had_soo_slot_) {
TransferSlotAfterSoo(c, SizeOfSlot);
}
} else if (old_capacity_ != 0 && grow_single_group) {
// SooEnabled implies that old_capacity_ != 0.
} else if ((SooEnabled || old_capacity_ != 0) && grow_single_group) {
if (TransferUsesMemcpy) {
GrowSizeIntoSingleGroupTransferable(c, SizeOfSlot);
DeallocateOld<AlignOfSlot>(alloc, SizeOfSlot);
......@@ -1923,7 +1944,7 @@ class HashSetResizeHelper {
c.set_has_infoz(has_infoz);
if (has_infoz) {
infoz.RecordStorageChanged(c.size(), layout.capacity());
if (was_soo_ || grow_single_group || old_capacity_ == 0) {
if ((SooEnabled && was_soo_) || grow_single_group || old_capacity_ == 0) {
infoz.RecordRehash(0);
}
c.set_infoz(infoz);
......@@ -2063,6 +2084,8 @@ class HashSetResizeHelper {
bool had_infoz_;
bool was_soo_;
bool had_soo_slot_;
// Either null infoz or a pre-sampled forced infoz for SOO tables.
HashtablezInfoHandle forced_infoz_;
};
inline void PrepareInsertCommon(CommonFields& common) {
......@@ -2545,6 +2568,8 @@ class raw_hash_set {
assert(size == 1);
common().set_full_soo();
emplace_at(soo_iterator(), *that.begin());
const HashtablezInfoHandle infoz = try_sample_soo();
if (infoz.IsSampled()) resize_with_soo_infoz(infoz);
return;
}
assert(!that.is_soo());
......@@ -2682,8 +2707,7 @@ class raw_hash_set {
size_t size() const { return common().size(); }
size_t capacity() const {
const size_t cap = common().capacity();
// Use local variables because compiler complains about using functions in
// assume.
// Compiler complains when using functions in assume so use local variables.
ABSL_ATTRIBUTE_UNUSED static constexpr bool kEnabled = SooEnabled();
ABSL_ATTRIBUTE_UNUSED static constexpr size_t kCapacity = SooCapacity();
ABSL_ASSUME(!kEnabled || cap >= kCapacity);
......@@ -3051,7 +3075,17 @@ class raw_hash_set {
SooEnabled());
return;
}
if (SooEnabled() && size() <= SooCapacity()) {
if (fits_in_soo(size())) {
// When the table is already sampled, we keep it sampled.
if (infoz().IsSampled()) {
const size_t kInitialSampledCapacity = NextCapacity(SooCapacity());
if (capacity() > kInitialSampledCapacity) {
resize(kInitialSampledCapacity);
}
// This asserts that we didn't lose sampling coverage in `resize`.
assert(infoz().IsSampled());
return;
}
alignas(slot_type) unsigned char slot_space[sizeof(slot_type)];
slot_type* tmp_slot = to_slot(slot_space);
transfer(tmp_slot, begin().slot());
......@@ -3322,6 +3356,15 @@ class raw_hash_set {
}
}
// Conditionally samples hashtablez for SOO tables. This should be called on
// insertion into an empty SOO table and in copy construction when the size
// can fit in SOO capacity.
inline HashtablezInfoHandle try_sample_soo() {
assert(is_soo());
if (!ShouldSampleHashtablezInfo<CharAlloc>()) return HashtablezInfoHandle{};
return Sample(sizeof(slot_type), SooCapacity());
}
inline void destroy_slots() {
assert(!is_soo());
if (PolicyTraits::template destroy_is_trivial<Alloc>()) return;
......@@ -3374,7 +3417,20 @@ class raw_hash_set {
// HashSetResizeHelper::FindFirstNonFullAfterResize(
// common(), old_capacity, hash)
// can be called right after `resize`.
ABSL_ATTRIBUTE_NOINLINE void resize(size_t new_capacity) {
void resize(size_t new_capacity) {
resize_impl(new_capacity, HashtablezInfoHandle{});
}
// As above, except that we also accept a pre-sampled, forced infoz for
// SOO tables, since they need to switch from SOO to heap in order to
// store the infoz.
void resize_with_soo_infoz(HashtablezInfoHandle forced_infoz) {
assert(forced_infoz.IsSampled());
resize_impl(NextCapacity(SooCapacity()), forced_infoz);
}
ABSL_ATTRIBUTE_NOINLINE void resize_impl(
size_t new_capacity, HashtablezInfoHandle forced_infoz) {
assert(IsValidCapacity(new_capacity));
assert(!fits_in_soo(new_capacity));
const bool was_soo = is_soo();
......@@ -3382,7 +3438,8 @@ class raw_hash_set {
const ctrl_t soo_slot_h2 =
had_soo_slot ? static_cast<ctrl_t>(H2(hash_of(soo_slot())))
: ctrl_t::kEmpty;
HashSetResizeHelper resize_helper(common(), was_soo, had_soo_slot);
HashSetResizeHelper resize_helper(common(), was_soo, had_soo_slot,
forced_infoz);
// Initialize HashSetResizeHelper::old_heap_or_soo_. We can't do this in
// HashSetResizeHelper constructor because it can't transfer slots when
// transfer_uses_memcpy is false.
......@@ -3400,7 +3457,7 @@ class raw_hash_set {
const bool grow_single_group =
resize_helper.InitializeSlots<CharAlloc, sizeof(slot_type),
PolicyTraits::transfer_uses_memcpy(),
alignof(slot_type)>(
SooEnabled(), alignof(slot_type)>(
common(), CharAlloc(alloc_ref()), soo_slot_h2);
// In the SooEnabled() case, capacity is never 0 so we don't check.
......@@ -3621,26 +3678,29 @@ class raw_hash_set {
return move_elements_allocs_unequal(std::move(that));
}
protected:
// Attempts to find `key` in the table; if it isn't found, returns an iterator
// where the value can be inserted into, with the control byte already set to
// `key`'s H2. Returns a bool indicating whether an insertion can take place.
template <class K>
std::pair<iterator, bool> find_or_prepare_insert(const K& key) {
if (is_soo()) {
if (empty()) {
std::pair<iterator, bool> find_or_prepare_insert_soo(const K& key) {
if (empty()) {
const HashtablezInfoHandle infoz = try_sample_soo();
if (infoz.IsSampled()) {
resize_with_soo_infoz(infoz);
} else {
common().set_full_soo();
return {soo_iterator(), true};
}
if (PolicyTraits::apply(EqualElement<K>{key, eq_ref()},
PolicyTraits::element(soo_slot()))) {
return {soo_iterator(), false};
}
} else if (PolicyTraits::apply(EqualElement<K>{key, eq_ref()},
PolicyTraits::element(soo_slot()))) {
return {soo_iterator(), false};
} else {
resize(NextCapacity(SooCapacity()));
const size_t index =
PrepareInsertAfterSoo(hash_ref()(key), sizeof(slot_type), common());
return {iterator_at(index), true};
}
const size_t index =
PrepareInsertAfterSoo(hash_ref()(key), sizeof(slot_type), common());
return {iterator_at(index), true};
}
template <class K>
std::pair<iterator, bool> find_or_prepare_insert_non_soo(const K& key) {
prefetch_heap_block();
auto hash = hash_ref()(key);
auto seq = probe(common(), hash);
......@@ -3660,6 +3720,16 @@ class raw_hash_set {
return {iterator_at(prepare_insert(hash)), true};
}
protected:
// Attempts to find `key` in the table; if it isn't found, returns an iterator
// where the value can be inserted into, with the control byte already set to
// `key`'s H2. Returns a bool indicating whether an insertion can take place.
template <class K>
std::pair<iterator, bool> find_or_prepare_insert(const K& key) {
if (is_soo()) return find_or_prepare_insert_soo(key);
return find_or_prepare_insert_non_soo(key);
}
// Given the hash of a value not currently in the table, finds the next
// viable slot index to insert it at.
//
......@@ -3769,13 +3839,13 @@ class raw_hash_set {
return static_cast<slot_type*>(common().soo_data());
}
const slot_type* soo_slot() const {
return reinterpret_cast<raw_hash_set*>(this)->soo_slot();
return const_cast<raw_hash_set*>(this)->soo_slot();
}
iterator soo_iterator() {
return {SooControl(), soo_slot(), common().generation_ptr()};
}
const_iterator soo_iterator() const {
return reinterpret_cast<raw_hash_set*>(this)->soo_iterator();
return const_cast<raw_hash_set*>(this)->soo_iterator();
}
HashtablezInfoHandle infoz() {
assert(!is_soo());
......
absl/container/internal/raw_hash_set_test.cc
......@@ -52,7 +52,9 @@
#include "absl/container/internal/hashtable_debug.h"
#include "absl/container/internal/hashtablez_sampler.h"
#include "absl/container/internal/test_allocator.h"
#include "absl/functional/function_ref.h"
#include "absl/hash/hash.h"
#include "absl/log/check.h"
#include "absl/log/log.h"
#include "absl/memory/memory.h"
#include "absl/meta/type_traits.h"
......@@ -2035,6 +2037,9 @@ TYPED_TEST_P(SooTest, FindFullDeletedRegression) {
}
TYPED_TEST_P(SooTest, ReplacingDeletedSlotDoesNotRehash) {
// We need to disable hashtablez to avoid issues related to SOO and sampling.
SetHashtablezEnabled(false);
size_t n;
{
// Compute n such that n is the maximum number of elements before rehash.
......@@ -2388,6 +2393,9 @@ TYPED_TEST_P(SooTest, IterationOrderChangesOnRehash) {
// Verify that pointers are invalidated as soon as a second element is inserted.
// This prevents dependency on pointer stability on small tables.
TYPED_TEST_P(SooTest, UnstablePointers) {
// We need to disable hashtablez to avoid issues related to SOO and sampling.
SetHashtablezEnabled(false);
TypeParam table;
const auto addr = [&](int i) {
......@@ -2523,7 +2531,7 @@ TYPED_TEST_P(RawHashSamplerTest, Sample) {
constexpr bool soo_enabled = std::is_same<SooIntTable, TypeParam>::value;
// Enable the feature even if the prod default is off.
SetHashtablezEnabled(true);
SetHashtablezSampleParameter(100);
SetHashtablezSampleParameter(100); // Sample ~1% of tables.
auto& sampler = GlobalHashtablezSampler();
size_t start_size = 0;
......@@ -2557,25 +2565,26 @@ TYPED_TEST_P(RawHashSamplerTest, Sample) {
absl::flat_hash_map<size_t, int> observed_checksums;
absl::flat_hash_map<ssize_t, int> reservations;
end_size += sampler.Iterate([&](const HashtablezInfo& info) {
if (preexisting_info.count(&info) == 0) {
observed_checksums[info.hashes_bitwise_xor.load(
std::memory_order_relaxed)]++;
reservations[info.max_reserve.load(std::memory_order_relaxed)]++;
}
EXPECT_EQ(info.inline_element_size, sizeof(typename TypeParam::value_type));
++end_size;
if (preexisting_info.contains(&info)) return;
observed_checksums[info.hashes_bitwise_xor.load(
std::memory_order_relaxed)]++;
reservations[info.max_reserve.load(std::memory_order_relaxed)]++;
EXPECT_EQ(info.inline_element_size, sizeof(typename TypeParam::value_type));
if (soo_enabled) {
EXPECT_EQ(info.soo_capacity, SooCapacity());
} else {
EXPECT_EQ(info.soo_capacity, 0);
}
});
// Expect that we sampled at the requested sampling rate of ~1%.
EXPECT_NEAR((end_size - start_size) / static_cast<double>(tables.size()),
0.01, 0.005);
if (soo_enabled) {
EXPECT_EQ(observed_checksums.size(), 9);
} else {
EXPECT_EQ(observed_checksums.size(), 5);
for (const auto& [_, count] : observed_checksums) {
EXPECT_NEAR((100 * count) / static_cast<double>(tables.size()), 0.2,
0.05);
}
EXPECT_EQ(observed_checksums.size(), 5);
for (const auto& [_, count] : observed_checksums) {
EXPECT_NEAR((100 * count) / static_cast<double>(tables.size()), 0.2, 0.05);
}
EXPECT_EQ(reservations.size(), 10);
......@@ -2591,12 +2600,141 @@ TYPED_TEST_P(RawHashSamplerTest, Sample) {
REGISTER_TYPED_TEST_SUITE_P(RawHashSamplerTest, Sample);
using RawHashSamplerTestTypes = ::testing::Types<SooIntTable, NonSooIntTable>;
INSTANTIATE_TYPED_TEST_SUITE_P(My, RawHashSamplerTest, RawHashSamplerTestTypes);
std::vector<const HashtablezInfo*> SampleSooMutation(
absl::FunctionRef<void(SooIntTable&)> mutate_table) {
// Enable the feature even if the prod default is off.
SetHashtablezEnabled(true);
SetHashtablezSampleParameter(100); // Sample ~1% of tables.
auto& sampler = GlobalHashtablezSampler();
size_t start_size = 0;
absl::flat_hash_set<const HashtablezInfo*> preexisting_info;
start_size += sampler.Iterate([&](const HashtablezInfo& info) {
preexisting_info.insert(&info);
++start_size;
});
std::vector<SooIntTable> tables;
for (int i = 0; i < 1000000; ++i) {
tables.emplace_back();
mutate_table(tables.back());
}
size_t end_size = 0;
std::vector<const HashtablezInfo*> infos;
end_size += sampler.Iterate([&](const HashtablezInfo& info) {
++end_size;
if (preexisting_info.contains(&info)) return;
infos.push_back(&info);
});
// Expect that we sampled at the requested sampling rate of ~1%.
EXPECT_NEAR((end_size - start_size) / static_cast<double>(tables.size()),
0.01, 0.005);
return infos;
}
TEST(RawHashSamplerTest, SooTableInsertToEmpty) {
if (SooIntTable().capacity() != SooCapacity()) {
CHECK_LT(sizeof(void*), 8) << "missing SOO coverage";
GTEST_SKIP() << "not SOO on this platform";
}
std::vector<const HashtablezInfo*> infos =
SampleSooMutation([](SooIntTable& t) { t.insert(1); });
for (const HashtablezInfo* info : infos) {
ASSERT_EQ(info->inline_element_size,
sizeof(typename SooIntTable::value_type));
ASSERT_EQ(info->soo_capacity, SooCapacity());
ASSERT_EQ(info->capacity, NextCapacity(SooCapacity()));
ASSERT_EQ(info->size, 1);
ASSERT_EQ(info->max_reserve, 0);
ASSERT_EQ(info->num_erases, 0);
ASSERT_EQ(info->max_probe_length, 0);
ASSERT_EQ(info->total_probe_length, 0);
}
}
TEST(RawHashSamplerTest, SooTableReserveToEmpty) {
if (SooIntTable().capacity() != SooCapacity()) {
CHECK_LT(sizeof(void*), 8) << "missing SOO coverage";
GTEST_SKIP() << "not SOO on this platform";
}
std::vector<const HashtablezInfo*> infos =
SampleSooMutation([](SooIntTable& t) { t.reserve(100); });
for (const HashtablezInfo* info : infos) {
ASSERT_EQ(info->inline_element_size,
sizeof(typename SooIntTable::value_type));
ASSERT_EQ(info->soo_capacity, SooCapacity());
ASSERT_GE(info->capacity, 100);
ASSERT_EQ(info->size, 0);
ASSERT_EQ(info->max_reserve, 100);
ASSERT_EQ(info->num_erases, 0);
ASSERT_EQ(info->max_probe_length, 0);
ASSERT_EQ(info->total_probe_length, 0);
}
}
// This tests that reserve on a full SOO table doesn't incorrectly result in new
// (over-)sampling.
TEST(RawHashSamplerTest, SooTableReserveToFullSoo) {
if (SooIntTable().capacity() != SooCapacity()) {
CHECK_LT(sizeof(void*), 8) << "missing SOO coverage";
GTEST_SKIP() << "not SOO on this platform";
}
std::vector<const HashtablezInfo*> infos =
SampleSooMutation([](SooIntTable& t) {
t.insert(1);
t.reserve(100);
});
for (const HashtablezInfo* info : infos) {
ASSERT_EQ(info->inline_element_size,
sizeof(typename SooIntTable::value_type));
ASSERT_EQ(info->soo_capacity, SooCapacity());
ASSERT_GE(info->capacity, 100);
ASSERT_EQ(info->size, 1);
ASSERT_EQ(info->max_reserve, 100);
ASSERT_EQ(info->num_erases, 0);
ASSERT_EQ(info->max_probe_length, 0);
ASSERT_EQ(info->total_probe_length, 0);
}
}
// This tests that rehash(0) on a sampled table with size that fits in SOO
// doesn't incorrectly result in losing sampling.
TEST(RawHashSamplerTest, SooTableRehashShrinkWhenSizeFitsInSoo) {
if (SooIntTable().capacity() != SooCapacity()) {
CHECK_LT(sizeof(void*), 8) << "missing SOO coverage";
GTEST_SKIP() << "not SOO on this platform";
}
std::vector<const HashtablezInfo*> infos =
SampleSooMutation([](SooIntTable& t) {
t.reserve(100);
t.insert(1);
EXPECT_GE(t.capacity(), 100);
t.rehash(0);
});
for (const HashtablezInfo* info : infos) {
ASSERT_EQ(info->inline_element_size,
sizeof(typename SooIntTable::value_type));
ASSERT_EQ(info->soo_capacity, SooCapacity());
ASSERT_EQ(info->capacity, NextCapacity(SooCapacity()));
ASSERT_EQ(info->size, 1);
ASSERT_EQ(info->max_reserve, 100);
ASSERT_EQ(info->num_erases, 0);
ASSERT_EQ(info->max_probe_length, 0);
ASSERT_EQ(info->total_probe_length, 0);
}
}
#endif // ABSL_INTERNAL_HASHTABLEZ_SAMPLE
TEST(RawHashSamplerTest, DoNotSampleCustomAllocators) {
// Enable the feature even if the prod default is off.
SetHashtablezEnabled(true);
SetHashtablezSampleParameter(100);
SetHashtablezSampleParameter(100); // Sample ~1% of tables.
auto& sampler = GlobalHashtablezSampler();
size_t start_size = 0;
......@@ -2974,7 +3112,7 @@ TYPED_TEST_P(SooTable, Basic) {
bool frozen = true;
TypeParam t{FreezableAlloc<typename TypeParam::value_type>(&frozen)};
if (t.capacity() != SooCapacity()) {
EXPECT_LT(sizeof(void*), 8);
CHECK_LT(sizeof(void*), 8) << "missing SOO coverage";
GTEST_SKIP() << "not SOO on this platform";
}
......@@ -3006,14 +3144,18 @@ using FreezableSooTableTypes =
FreezableSizedValueSooTable<16>>;
INSTANTIATE_TYPED_TEST_SUITE_P(My, SooTable, FreezableSooTableTypes);
TEST(Table, RehashToSoo) {
TEST(Table, RehashToSooUnsampled) {
SooIntTable t;
if (t.capacity() != SooCapacity()) {
EXPECT_LT(sizeof(void*), 8);
CHECK_LT(sizeof(void*), 8) << "missing SOO coverage";
GTEST_SKIP() << "not SOO on this platform";
}
t.reserve(10);
// We disable hashtablez sampling for this test to ensure that the table isn't
// sampled. When the table is sampled, it won't rehash down to SOO.
SetHashtablezEnabled(false);
t.reserve(100);
t.insert(0);
EXPECT_EQ(*t.begin(), 0);
......@@ -3026,7 +3168,7 @@ TEST(Table, RehashToSoo) {
EXPECT_EQ(t.find(1), t.end());
}
TEST(Table, ResizeToNonSoo) {
TEST(Table, ReserveToNonSoo) {
for (int reserve_capacity : {8, 100000}) {
SooIntTable t;
t.insert(0);
......
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