Abseil Common Libraries (C++) (grcp 依赖)
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297 lines
10 KiB
297 lines
10 KiB
// Copyright 2018 The Abseil Authors. |
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// |
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// Licensed under the Apache License, Version 2.0 (the "License"); |
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// you may not use this file except in compliance with the License. |
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// You may obtain a copy of the License at |
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// |
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// https://www.apache.org/licenses/LICENSE-2.0 |
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// |
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// Unless required by applicable law or agreed to in writing, software |
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// distributed under the License is distributed on an "AS IS" BASIS, |
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
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// See the License for the specific language governing permissions and |
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// limitations under the License. |
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// |
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// ----------------------------------------------------------------------------- |
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// File: hashtablez_sampler.h |
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// ----------------------------------------------------------------------------- |
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// |
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// This header file defines the API for a low level library to sample hashtables |
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// and collect runtime statistics about them. |
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// |
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// `HashtablezSampler` controls the lifecycle of `HashtablezInfo` objects which |
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// store information about a single sample. |
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// |
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// `Record*` methods store information into samples. |
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// `Sample()` and `Unsample()` make use of a single global sampler with |
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// properties controlled by the flags hashtablez_enabled, |
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// hashtablez_sample_rate, and hashtablez_max_samples. |
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// |
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// WARNING |
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// |
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// Using this sampling API may cause sampled Swiss tables to use the global |
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// allocator (operator `new`) in addition to any custom allocator. If you |
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// are using a table in an unusual circumstance where allocation or calling a |
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// linux syscall is unacceptable, this could interfere. |
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// |
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// This utility is internal-only. Use at your own risk. |
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#ifndef ABSL_CONTAINER_INTERNAL_HASHTABLEZ_SAMPLER_H_ |
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#define ABSL_CONTAINER_INTERNAL_HASHTABLEZ_SAMPLER_H_ |
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#include <atomic> |
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#include <functional> |
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#include <memory> |
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#include <vector> |
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#include "absl/base/internal/per_thread_tls.h" |
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#include "absl/base/optimization.h" |
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#include "absl/container/internal/have_sse.h" |
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#include "absl/synchronization/mutex.h" |
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#include "absl/utility/utility.h" |
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namespace absl { |
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ABSL_NAMESPACE_BEGIN |
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namespace container_internal { |
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// Stores information about a sampled hashtable. All mutations to this *must* |
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// be made through `Record*` functions below. All reads from this *must* only |
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// occur in the callback to `HashtablezSampler::Iterate`. |
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struct HashtablezInfo { |
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// Constructs the object but does not fill in any fields. |
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HashtablezInfo(); |
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~HashtablezInfo(); |
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HashtablezInfo(const HashtablezInfo&) = delete; |
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HashtablezInfo& operator=(const HashtablezInfo&) = delete; |
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// Puts the object into a clean state, fills in the logically `const` members, |
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// blocking for any readers that are currently sampling the object. |
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void PrepareForSampling() ABSL_EXCLUSIVE_LOCKS_REQUIRED(init_mu); |
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// These fields are mutated by the various Record* APIs and need to be |
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// thread-safe. |
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std::atomic<size_t> capacity; |
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std::atomic<size_t> size; |
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std::atomic<size_t> num_erases; |
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std::atomic<size_t> max_probe_length; |
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std::atomic<size_t> total_probe_length; |
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std::atomic<size_t> hashes_bitwise_or; |
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std::atomic<size_t> hashes_bitwise_and; |
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// `HashtablezSampler` maintains intrusive linked lists for all samples. See |
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// comments on `HashtablezSampler::all_` for details on these. `init_mu` |
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// guards the ability to restore the sample to a pristine state. This |
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// prevents races with sampling and resurrecting an object. |
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absl::Mutex init_mu; |
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HashtablezInfo* next; |
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HashtablezInfo* dead ABSL_GUARDED_BY(init_mu); |
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// All of the fields below are set by `PrepareForSampling`, they must not be |
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// mutated in `Record*` functions. They are logically `const` in that sense. |
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// These are guarded by init_mu, but that is not externalized to clients, who |
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// can only read them during `HashtablezSampler::Iterate` which will hold the |
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// lock. |
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static constexpr int kMaxStackDepth = 64; |
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absl::Time create_time; |
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int32_t depth; |
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void* stack[kMaxStackDepth]; |
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}; |
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inline void RecordRehashSlow(HashtablezInfo* info, size_t total_probe_length) { |
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#if SWISSTABLE_HAVE_SSE2 |
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total_probe_length /= 16; |
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#else |
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total_probe_length /= 8; |
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#endif |
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info->total_probe_length.store(total_probe_length, std::memory_order_relaxed); |
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info->num_erases.store(0, std::memory_order_relaxed); |
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} |
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inline void RecordStorageChangedSlow(HashtablezInfo* info, size_t size, |
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size_t capacity) { |
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info->size.store(size, std::memory_order_relaxed); |
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info->capacity.store(capacity, std::memory_order_relaxed); |
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if (size == 0) { |
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// This is a clear, reset the total/num_erases too. |
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RecordRehashSlow(info, 0); |
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} |
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} |
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void RecordInsertSlow(HashtablezInfo* info, size_t hash, |
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size_t distance_from_desired); |
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inline void RecordEraseSlow(HashtablezInfo* info) { |
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info->size.fetch_sub(1, std::memory_order_relaxed); |
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info->num_erases.fetch_add(1, std::memory_order_relaxed); |
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} |
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HashtablezInfo* SampleSlow(int64_t* next_sample); |
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void UnsampleSlow(HashtablezInfo* info); |
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class HashtablezInfoHandle { |
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public: |
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explicit HashtablezInfoHandle() : info_(nullptr) {} |
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explicit HashtablezInfoHandle(HashtablezInfo* info) : info_(info) {} |
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~HashtablezInfoHandle() { |
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if (ABSL_PREDICT_TRUE(info_ == nullptr)) return; |
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UnsampleSlow(info_); |
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} |
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HashtablezInfoHandle(const HashtablezInfoHandle&) = delete; |
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HashtablezInfoHandle& operator=(const HashtablezInfoHandle&) = delete; |
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HashtablezInfoHandle(HashtablezInfoHandle&& o) noexcept |
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: info_(absl::exchange(o.info_, nullptr)) {} |
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HashtablezInfoHandle& operator=(HashtablezInfoHandle&& o) noexcept { |
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if (ABSL_PREDICT_FALSE(info_ != nullptr)) { |
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UnsampleSlow(info_); |
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} |
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info_ = absl::exchange(o.info_, nullptr); |
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return *this; |
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} |
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inline void RecordStorageChanged(size_t size, size_t capacity) { |
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if (ABSL_PREDICT_TRUE(info_ == nullptr)) return; |
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RecordStorageChangedSlow(info_, size, capacity); |
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} |
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inline void RecordRehash(size_t total_probe_length) { |
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if (ABSL_PREDICT_TRUE(info_ == nullptr)) return; |
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RecordRehashSlow(info_, total_probe_length); |
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} |
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inline void RecordInsert(size_t hash, size_t distance_from_desired) { |
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if (ABSL_PREDICT_TRUE(info_ == nullptr)) return; |
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RecordInsertSlow(info_, hash, distance_from_desired); |
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} |
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inline void RecordErase() { |
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if (ABSL_PREDICT_TRUE(info_ == nullptr)) return; |
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RecordEraseSlow(info_); |
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} |
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friend inline void swap(HashtablezInfoHandle& lhs, |
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HashtablezInfoHandle& rhs) { |
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std::swap(lhs.info_, rhs.info_); |
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} |
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private: |
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friend class HashtablezInfoHandlePeer; |
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HashtablezInfo* info_; |
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}; |
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#if defined(ABSL_INTERNAL_HASHTABLEZ_SAMPLE) |
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#error ABSL_INTERNAL_HASHTABLEZ_SAMPLE cannot be directly set |
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#endif // defined(ABSL_INTERNAL_HASHTABLEZ_SAMPLE) |
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#if (ABSL_PER_THREAD_TLS == 1) && !defined(ABSL_BUILD_DLL) && \ |
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!defined(ABSL_CONSUME_DLL) |
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#define ABSL_INTERNAL_HASHTABLEZ_SAMPLE |
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#endif |
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#if defined(ABSL_INTERNAL_HASHTABLEZ_SAMPLE) |
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extern ABSL_PER_THREAD_TLS_KEYWORD int64_t global_next_sample; |
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#endif // ABSL_PER_THREAD_TLS |
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// Returns an RAII sampling handle that manages registration and unregistation |
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// with the global sampler. |
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inline HashtablezInfoHandle Sample() { |
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#if defined(ABSL_INTERNAL_HASHTABLEZ_SAMPLE) |
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if (ABSL_PREDICT_TRUE(--global_next_sample > 0)) { |
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return HashtablezInfoHandle(nullptr); |
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} |
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return HashtablezInfoHandle(SampleSlow(&global_next_sample)); |
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#else |
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return HashtablezInfoHandle(nullptr); |
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#endif // !ABSL_PER_THREAD_TLS |
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} |
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// Holds samples and their associated stack traces with a soft limit of |
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// `SetHashtablezMaxSamples()`. |
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// |
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// Thread safe. |
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class HashtablezSampler { |
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public: |
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// Returns a global Sampler. |
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static HashtablezSampler& Global(); |
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HashtablezSampler(); |
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~HashtablezSampler(); |
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// Registers for sampling. Returns an opaque registration info. |
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HashtablezInfo* Register(); |
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// Unregisters the sample. |
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void Unregister(HashtablezInfo* sample); |
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// The dispose callback will be called on all samples the moment they are |
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// being unregistered. Only affects samples that are unregistered after the |
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// callback has been set. |
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// Returns the previous callback. |
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using DisposeCallback = void (*)(const HashtablezInfo&); |
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DisposeCallback SetDisposeCallback(DisposeCallback f); |
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// Iterates over all the registered `StackInfo`s. Returning the number of |
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// samples that have been dropped. |
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int64_t Iterate(const std::function<void(const HashtablezInfo& stack)>& f); |
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private: |
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void PushNew(HashtablezInfo* sample); |
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void PushDead(HashtablezInfo* sample); |
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HashtablezInfo* PopDead(); |
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std::atomic<size_t> dropped_samples_; |
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std::atomic<size_t> size_estimate_; |
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// Intrusive lock free linked lists for tracking samples. |
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// |
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// `all_` records all samples (they are never removed from this list) and is |
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// terminated with a `nullptr`. |
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// |
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// `graveyard_.dead` is a circular linked list. When it is empty, |
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// `graveyard_.dead == &graveyard`. The list is circular so that |
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// every item on it (even the last) has a non-null dead pointer. This allows |
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// `Iterate` to determine if a given sample is live or dead using only |
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// information on the sample itself. |
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// |
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// For example, nodes [A, B, C, D, E] with [A, C, E] alive and [B, D] dead |
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// looks like this (G is the Graveyard): |
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// |
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// +---+ +---+ +---+ +---+ +---+ |
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// all -->| A |--->| B |--->| C |--->| D |--->| E | |
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// | | | | | | | | | | |
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// +---+ | | +->| |-+ | | +->| |-+ | | |
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// | G | +---+ | +---+ | +---+ | +---+ | +---+ |
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// | | | | | | |
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// | | --------+ +--------+ | |
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// +---+ | |
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// ^ | |
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// +--------------------------------------+ |
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// |
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std::atomic<HashtablezInfo*> all_; |
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HashtablezInfo graveyard_; |
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std::atomic<DisposeCallback> dispose_; |
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}; |
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// Enables or disables sampling for Swiss tables. |
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void SetHashtablezEnabled(bool enabled); |
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// Sets the rate at which Swiss tables will be sampled. |
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void SetHashtablezSampleParameter(int32_t rate); |
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// Sets a soft max for the number of samples that will be kept. |
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void SetHashtablezMaxSamples(int32_t max); |
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// Configuration override. |
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// This allows process-wide sampling without depending on order of |
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// initialization of static storage duration objects. |
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// The definition of this constant is weak, which allows us to inject a |
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// different value for it at link time. |
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extern "C" bool AbslContainerInternalSampleEverything(); |
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} // namespace container_internal |
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ABSL_NAMESPACE_END |
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} // namespace absl |
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#endif // ABSL_CONTAINER_INTERNAL_HASHTABLEZ_SAMPLER_H_
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