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Diffstat (limited to 'third_party/abseil_cpp/absl/container/internal/hashtablez_sampler.cc')
-rw-r--r-- | third_party/abseil_cpp/absl/container/internal/hashtablez_sampler.cc | 270 |
1 files changed, 270 insertions, 0 deletions
diff --git a/third_party/abseil_cpp/absl/container/internal/hashtablez_sampler.cc b/third_party/abseil_cpp/absl/container/internal/hashtablez_sampler.cc new file mode 100644 index 000000000000..e4484fbb1b43 --- /dev/null +++ b/third_party/abseil_cpp/absl/container/internal/hashtablez_sampler.cc @@ -0,0 +1,270 @@ +// 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/hashtablez_sampler.h" + +#include <atomic> +#include <cassert> +#include <cmath> +#include <functional> +#include <limits> + +#include "absl/base/attributes.h" +#include "absl/base/internal/exponential_biased.h" +#include "absl/container/internal/have_sse.h" +#include "absl/debugging/stacktrace.h" +#include "absl/memory/memory.h" +#include "absl/synchronization/mutex.h" + +namespace absl { +ABSL_NAMESPACE_BEGIN +namespace container_internal { +constexpr int HashtablezInfo::kMaxStackDepth; + +namespace { +ABSL_CONST_INIT std::atomic<bool> g_hashtablez_enabled{ + false +}; +ABSL_CONST_INIT std::atomic<int32_t> g_hashtablez_sample_parameter{1 << 10}; +ABSL_CONST_INIT std::atomic<int32_t> g_hashtablez_max_samples{1 << 20}; + +#if defined(ABSL_INTERNAL_HASHTABLEZ_SAMPLE) +ABSL_PER_THREAD_TLS_KEYWORD absl::base_internal::ExponentialBiased + g_exponential_biased_generator; +#endif + +} // namespace + +#if defined(ABSL_INTERNAL_HASHTABLEZ_SAMPLE) +ABSL_PER_THREAD_TLS_KEYWORD int64_t global_next_sample = 0; +#endif // defined(ABSL_INTERNAL_HASHTABLEZ_SAMPLE) + +HashtablezSampler& HashtablezSampler::Global() { + static auto* sampler = new HashtablezSampler(); + return *sampler; +} + +HashtablezSampler::DisposeCallback HashtablezSampler::SetDisposeCallback( + DisposeCallback f) { + return dispose_.exchange(f, std::memory_order_relaxed); +} + +HashtablezInfo::HashtablezInfo() { PrepareForSampling(); } +HashtablezInfo::~HashtablezInfo() = default; + +void HashtablezInfo::PrepareForSampling() { + capacity.store(0, std::memory_order_relaxed); + size.store(0, std::memory_order_relaxed); + num_erases.store(0, std::memory_order_relaxed); + num_rehashes.store(0, std::memory_order_relaxed); + max_probe_length.store(0, std::memory_order_relaxed); + total_probe_length.store(0, std::memory_order_relaxed); + hashes_bitwise_or.store(0, std::memory_order_relaxed); + hashes_bitwise_and.store(~size_t{}, std::memory_order_relaxed); + + create_time = absl::Now(); + // The inliner makes hardcoded skip_count difficult (especially when combined + // with LTO). We use the ability to exclude stacks by regex when encoding + // instead. + depth = absl::GetStackTrace(stack, HashtablezInfo::kMaxStackDepth, + /* skip_count= */ 0); + dead = nullptr; +} + +HashtablezSampler::HashtablezSampler() + : dropped_samples_(0), size_estimate_(0), all_(nullptr), dispose_(nullptr) { + absl::MutexLock l(&graveyard_.init_mu); + graveyard_.dead = &graveyard_; +} + +HashtablezSampler::~HashtablezSampler() { + HashtablezInfo* s = all_.load(std::memory_order_acquire); + while (s != nullptr) { + HashtablezInfo* next = s->next; + delete s; + s = next; + } +} + +void HashtablezSampler::PushNew(HashtablezInfo* sample) { + sample->next = all_.load(std::memory_order_relaxed); + while (!all_.compare_exchange_weak(sample->next, sample, + std::memory_order_release, + std::memory_order_relaxed)) { + } +} + +void HashtablezSampler::PushDead(HashtablezInfo* sample) { + if (auto* dispose = dispose_.load(std::memory_order_relaxed)) { + dispose(*sample); + } + + absl::MutexLock graveyard_lock(&graveyard_.init_mu); + absl::MutexLock sample_lock(&sample->init_mu); + sample->dead = graveyard_.dead; + graveyard_.dead = sample; +} + +HashtablezInfo* HashtablezSampler::PopDead() { + absl::MutexLock graveyard_lock(&graveyard_.init_mu); + + // The list is circular, so eventually it collapses down to + // graveyard_.dead == &graveyard_ + // when it is empty. + HashtablezInfo* sample = graveyard_.dead; + if (sample == &graveyard_) return nullptr; + + absl::MutexLock sample_lock(&sample->init_mu); + graveyard_.dead = sample->dead; + sample->PrepareForSampling(); + return sample; +} + +HashtablezInfo* HashtablezSampler::Register() { + int64_t size = size_estimate_.fetch_add(1, std::memory_order_relaxed); + if (size > g_hashtablez_max_samples.load(std::memory_order_relaxed)) { + size_estimate_.fetch_sub(1, std::memory_order_relaxed); + dropped_samples_.fetch_add(1, std::memory_order_relaxed); + return nullptr; + } + + HashtablezInfo* sample = PopDead(); + if (sample == nullptr) { + // Resurrection failed. Hire a new warlock. + sample = new HashtablezInfo(); + PushNew(sample); + } + + return sample; +} + +void HashtablezSampler::Unregister(HashtablezInfo* sample) { + PushDead(sample); + size_estimate_.fetch_sub(1, std::memory_order_relaxed); +} + +int64_t HashtablezSampler::Iterate( + const std::function<void(const HashtablezInfo& stack)>& f) { + HashtablezInfo* s = all_.load(std::memory_order_acquire); + while (s != nullptr) { + absl::MutexLock l(&s->init_mu); + if (s->dead == nullptr) { + f(*s); + } + s = s->next; + } + + return dropped_samples_.load(std::memory_order_relaxed); +} + +static bool ShouldForceSampling() { + enum ForceState { + kDontForce, + kForce, + kUninitialized + }; + ABSL_CONST_INIT static std::atomic<ForceState> global_state{ + kUninitialized}; + ForceState state = global_state.load(std::memory_order_relaxed); + if (ABSL_PREDICT_TRUE(state == kDontForce)) return false; + + if (state == kUninitialized) { + state = AbslContainerInternalSampleEverything() ? kForce : kDontForce; + global_state.store(state, std::memory_order_relaxed); + } + return state == kForce; +} + +HashtablezInfo* SampleSlow(int64_t* next_sample) { + if (ABSL_PREDICT_FALSE(ShouldForceSampling())) { + *next_sample = 1; + return HashtablezSampler::Global().Register(); + } + +#if !defined(ABSL_INTERNAL_HASHTABLEZ_SAMPLE) + *next_sample = std::numeric_limits<int64_t>::max(); + return nullptr; +#else + bool first = *next_sample < 0; + *next_sample = g_exponential_biased_generator.GetStride( + g_hashtablez_sample_parameter.load(std::memory_order_relaxed)); + // Small values of interval are equivalent to just sampling next time. + ABSL_ASSERT(*next_sample >= 1); + + // g_hashtablez_enabled can be dynamically flipped, we need to set a threshold + // low enough that we will start sampling in a reasonable time, so we just use + // the default sampling rate. + if (!g_hashtablez_enabled.load(std::memory_order_relaxed)) return nullptr; + + // We will only be negative on our first count, so we should just retry in + // that case. + if (first) { + if (ABSL_PREDICT_TRUE(--*next_sample > 0)) return nullptr; + return SampleSlow(next_sample); + } + + return HashtablezSampler::Global().Register(); +#endif +} + +void UnsampleSlow(HashtablezInfo* info) { + HashtablezSampler::Global().Unregister(info); +} + +void RecordInsertSlow(HashtablezInfo* info, size_t hash, + size_t distance_from_desired) { + // SwissTables probe in groups of 16, so scale this to count items probes and + // not offset from desired. + size_t probe_length = distance_from_desired; +#if ABSL_INTERNAL_RAW_HASH_SET_HAVE_SSE2 + probe_length /= 16; +#else + probe_length /= 8; +#endif + + info->hashes_bitwise_and.fetch_and(hash, std::memory_order_relaxed); + info->hashes_bitwise_or.fetch_or(hash, std::memory_order_relaxed); + info->max_probe_length.store( + std::max(info->max_probe_length.load(std::memory_order_relaxed), + probe_length), + std::memory_order_relaxed); + info->total_probe_length.fetch_add(probe_length, std::memory_order_relaxed); + info->size.fetch_add(1, std::memory_order_relaxed); +} + +void SetHashtablezEnabled(bool enabled) { + g_hashtablez_enabled.store(enabled, std::memory_order_release); +} + +void SetHashtablezSampleParameter(int32_t rate) { + if (rate > 0) { + g_hashtablez_sample_parameter.store(rate, std::memory_order_release); + } else { + ABSL_RAW_LOG(ERROR, "Invalid hashtablez sample rate: %lld", + static_cast<long long>(rate)); // NOLINT(runtime/int) + } +} + +void SetHashtablezMaxSamples(int32_t max) { + if (max > 0) { + g_hashtablez_max_samples.store(max, std::memory_order_release); + } else { + ABSL_RAW_LOG(ERROR, "Invalid hashtablez max samples: %lld", + static_cast<long long>(max)); // NOLINT(runtime/int) + } +} + +} // namespace container_internal +ABSL_NAMESPACE_END +} // namespace absl |