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Diffstat (limited to 'third_party/abseil-cpp/absl/profiling/internal/sample_recorder.h')
| -rw-r--r-- | third_party/abseil-cpp/absl/profiling/internal/sample_recorder.h | 230 |
1 files changed, 230 insertions, 0 deletions
diff --git a/third_party/abseil-cpp/absl/profiling/internal/sample_recorder.h b/third_party/abseil-cpp/absl/profiling/internal/sample_recorder.h new file mode 100644 index 0000000000..5e04a9cd19 --- /dev/null +++ b/third_party/abseil-cpp/absl/profiling/internal/sample_recorder.h @@ -0,0 +1,230 @@ +// 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. +// +// ----------------------------------------------------------------------------- +// File: sample_recorder.h +// ----------------------------------------------------------------------------- +// +// This header file defines a lock-free linked list for recording samples +// collected from a random/stochastic process. +// +// This utility is internal-only. Use at your own risk. + +#ifndef ABSL_PROFILING_INTERNAL_SAMPLE_RECORDER_H_ +#define ABSL_PROFILING_INTERNAL_SAMPLE_RECORDER_H_ + +#include <atomic> +#include <cstddef> +#include <functional> + +#include "absl/base/config.h" +#include "absl/base/thread_annotations.h" +#include "absl/synchronization/mutex.h" +#include "absl/time/time.h" + +namespace absl { +ABSL_NAMESPACE_BEGIN +namespace profiling_internal { + +// Sample<T> that has members required for linking samples in the linked list of +// samples maintained by the SampleRecorder. Type T defines the sampled data. +template <typename T> +struct Sample { + // Guards the ability to restore the sample to a pristine state. This + // prevents races with sampling and resurrecting an object. + absl::Mutex init_mu; + T* next = nullptr; + T* dead ABSL_GUARDED_BY(init_mu) = nullptr; +}; + +// Holds samples and their associated stack traces with a soft limit of +// `SetHashtablezMaxSamples()`. +// +// Thread safe. +template <typename T> +class SampleRecorder { + public: + SampleRecorder(); + ~SampleRecorder(); + + // Registers for sampling. Returns an opaque registration info. + T* Register(); + + // Unregisters the sample. + void Unregister(T* sample); + + // The dispose callback will be called on all samples the moment they are + // being unregistered. Only affects samples that are unregistered after the + // callback has been set. + // Returns the previous callback. + using DisposeCallback = void (*)(const T&); + DisposeCallback SetDisposeCallback(DisposeCallback f); + + // Iterates over all the registered `StackInfo`s. Returning the number of + // samples that have been dropped. + int64_t Iterate(const std::function<void(const T& stack)>& f); + + void SetMaxSamples(int32_t max); + + private: + void PushNew(T* sample); + void PushDead(T* sample); + T* PopDead(); + + std::atomic<size_t> dropped_samples_; + std::atomic<size_t> size_estimate_; + std::atomic<int32_t> max_samples_{1 << 20}; + + // Intrusive lock free linked lists for tracking samples. + // + // `all_` records all samples (they are never removed from this list) and is + // terminated with a `nullptr`. + // + // `graveyard_.dead` is a circular linked list. When it is empty, + // `graveyard_.dead == &graveyard`. The list is circular so that + // every item on it (even the last) has a non-null dead pointer. This allows + // `Iterate` to determine if a given sample is live or dead using only + // information on the sample itself. + // + // For example, nodes [A, B, C, D, E] with [A, C, E] alive and [B, D] dead + // looks like this (G is the Graveyard): + // + // +---+ +---+ +---+ +---+ +---+ + // all -->| A |--->| B |--->| C |--->| D |--->| E | + // | | | | | | | | | | + // +---+ | | +->| |-+ | | +->| |-+ | | + // | G | +---+ | +---+ | +---+ | +---+ | +---+ + // | | | | | | + // | | --------+ +--------+ | + // +---+ | + // ^ | + // +--------------------------------------+ + // + std::atomic<T*> all_; + T graveyard_; + + std::atomic<DisposeCallback> dispose_; +}; + +template <typename T> +typename SampleRecorder<T>::DisposeCallback +SampleRecorder<T>::SetDisposeCallback(DisposeCallback f) { + return dispose_.exchange(f, std::memory_order_relaxed); +} + +template <typename T> +SampleRecorder<T>::SampleRecorder() + : dropped_samples_(0), size_estimate_(0), all_(nullptr), dispose_(nullptr) { + absl::MutexLock l(&graveyard_.init_mu); + graveyard_.dead = &graveyard_; +} + +template <typename T> +SampleRecorder<T>::~SampleRecorder() { + T* s = all_.load(std::memory_order_acquire); + while (s != nullptr) { + T* next = s->next; + delete s; + s = next; + } +} + +template <typename T> +void SampleRecorder<T>::PushNew(T* 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)) { + } +} + +template <typename T> +void SampleRecorder<T>::PushDead(T* 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; +} + +template <typename T> +T* SampleRecorder<T>::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. + T* sample = graveyard_.dead; + if (sample == &graveyard_) return nullptr; + + absl::MutexLock sample_lock(&sample->init_mu); + graveyard_.dead = sample->dead; + sample->dead = nullptr; + sample->PrepareForSampling(); + return sample; +} + +template <typename T> +T* SampleRecorder<T>::Register() { + int64_t size = size_estimate_.fetch_add(1, std::memory_order_relaxed); + if (size > 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; + } + + T* sample = PopDead(); + if (sample == nullptr) { + // Resurrection failed. Hire a new warlock. + sample = new T(); + PushNew(sample); + } + + return sample; +} + +template <typename T> +void SampleRecorder<T>::Unregister(T* sample) { + PushDead(sample); + size_estimate_.fetch_sub(1, std::memory_order_relaxed); +} + +template <typename T> +int64_t SampleRecorder<T>::Iterate( + const std::function<void(const T& stack)>& f) { + T* 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); +} + +template <typename T> +void SampleRecorder<T>::SetMaxSamples(int32_t max) { + max_samples_.store(max, std::memory_order_release); +} + +} // namespace profiling_internal +ABSL_NAMESPACE_END +} // namespace absl + +#endif // ABSL_PROFILING_INTERNAL_SAMPLE_RECORDER_H_ |