hashtablez_sampler.h | Explore in Territory

// 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: hashtablez_sampler.h
// -----------------------------------------------------------------------------
//
// This header file defines the API for a low level library to sample hashtables
// and collect runtime statistics about them.
//
// `HashtablezSampler` controls the lifecycle of `HashtablezInfo` objects which
// store information about a single sample.
//
// `Record*` methods store information into samples.
// `Sample()` and `Unsample()` make use of a single global sampler with
// properties controlled by the flags hashtablez_enabled,
// hashtablez_sample_rate, and hashtablez_max_samples.
//
// WARNING
//
// Using this sampling API may cause sampled Swiss tables to use the global
// allocator (operator `new`) in addition to any custom allocator.  If you
// are using a table in an unusual circumstance where allocation or calling a
// linux syscall is unacceptable, this could interfere.
//
// This utility is internal-only. Use at your own risk.

#ifndef ABSL_CONTAINER_INTERNAL_HASHTABLEZ_SAMPLER_H_
#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 {
ABSL_NAMESPACE_BEGIN
namespace container_internal {

// Stores information about a sampled hashtable.  All mutations to this *must*
// be made through `Record*` functions below.  All reads from this *must* only
// occur in the callback to `HashtablezSampler::Iterate`.
struct HashtablezInfo : public profiling_internal::Sample<HashtablezInfo> { … };

void RecordRehashSlow(HashtablezInfo* info, size_t total_probe_length);

void RecordReservationSlow(HashtablezInfo* info, size_t target_capacity);

void RecordClearedReservationSlow(HashtablezInfo* info);

void RecordStorageChangedSlow(HashtablezInfo* info, size_t size,
                              size_t capacity);

void RecordInsertSlow(HashtablezInfo* info, size_t hash,
                      size_t distance_from_desired);

void RecordEraseSlow(HashtablezInfo* info);

struct SamplingState { … };

HashtablezInfo* SampleSlow(SamplingState& next_sample,
                           size_t inline_element_size, size_t key_size,
                           size_t value_size, uint16_t soo_capacity);
void UnsampleSlow(HashtablezInfo* info);

#if defined(ABSL_INTERNAL_HASHTABLEZ_SAMPLE)
#error ABSL_INTERNAL_HASHTABLEZ_SAMPLE cannot be directly set
#endif  // defined(ABSL_INTERNAL_HASHTABLEZ_SAMPLE)

#if defined(ABSL_INTERNAL_HASHTABLEZ_SAMPLE)
class HashtablezInfoHandle {
 public:
  explicit HashtablezInfoHandle() : info_(nullptr) {}
  explicit HashtablezInfoHandle(HashtablezInfo* info) : info_(info) {}

  // We do not have a destructor. Caller is responsible for calling Unregister
  // before destroying the handle.
  void Unregister() {
    if (ABSL_PREDICT_TRUE(info_ == nullptr)) return;
    UnsampleSlow(info_);
  }

  inline bool IsSampled() const { return ABSL_PREDICT_FALSE(info_ != nullptr); }

  inline void RecordStorageChanged(size_t size, size_t capacity) {
    if (ABSL_PREDICT_TRUE(info_ == nullptr)) return;
    RecordStorageChangedSlow(info_, size, capacity);
  }

  inline void RecordRehash(size_t total_probe_length) {
    if (ABSL_PREDICT_TRUE(info_ == nullptr)) return;
    RecordRehashSlow(info_, total_probe_length);
  }

  inline void RecordReservation(size_t target_capacity) {
    if (ABSL_PREDICT_TRUE(info_ == nullptr)) return;
    RecordReservationSlow(info_, target_capacity);
  }

  inline void RecordClearedReservation() {
    if (ABSL_PREDICT_TRUE(info_ == nullptr)) return;
    RecordClearedReservationSlow(info_);
  }

  inline void RecordInsert(size_t hash, size_t distance_from_desired) {
    if (ABSL_PREDICT_TRUE(info_ == nullptr)) return;
    RecordInsertSlow(info_, hash, distance_from_desired);
  }

  inline void RecordErase() {
    if (ABSL_PREDICT_TRUE(info_ == nullptr)) return;
    RecordEraseSlow(info_);
  }

  friend inline void swap(HashtablezInfoHandle& lhs,
                          HashtablezInfoHandle& rhs) {
    std::swap(lhs.info_, rhs.info_);
  }

 private:
  friend class HashtablezInfoHandlePeer;
  HashtablezInfo* info_;
};
#else
// Ensure that when Hashtablez is turned off at compile time, HashtablezInfo can
// be removed by the linker, in order to reduce the binary size.
class HashtablezInfoHandle { … };
#endif  // defined(ABSL_INTERNAL_HASHTABLEZ_SAMPLE)

#if defined(ABSL_INTERNAL_HASHTABLEZ_SAMPLE)
extern ABSL_PER_THREAD_TLS_KEYWORD SamplingState global_next_sample;
#endif  // defined(ABSL_INTERNAL_HASHTABLEZ_SAMPLE)

// Returns a sampling handle.
inline HashtablezInfoHandle Sample(
    ABSL_ATTRIBUTE_UNUSED size_t inline_element_size,
    ABSL_ATTRIBUTE_UNUSED size_t key_size,
    ABSL_ATTRIBUTE_UNUSED size_t value_size,
    ABSL_ATTRIBUTE_UNUSED uint16_t soo_capacity) { … }

HashtablezSampler;

// Returns a global Sampler.
HashtablezSampler& GlobalHashtablezSampler();

HashtablezConfigListener;
void SetHashtablezConfigListener(HashtablezConfigListener l);

// Enables or disables sampling for Swiss tables.
bool IsHashtablezEnabled();
void SetHashtablezEnabled(bool enabled);
void SetHashtablezEnabledInternal(bool enabled);

// Sets the rate at which Swiss tables will be sampled.
int32_t GetHashtablezSampleParameter();
void SetHashtablezSampleParameter(int32_t rate);
void SetHashtablezSampleParameterInternal(int32_t rate);

// Sets a soft max for the number of samples that will be kept.
size_t GetHashtablezMaxSamples();
void SetHashtablezMaxSamples(size_t max);
void SetHashtablezMaxSamplesInternal(size_t max);

// Configuration override.
// This allows process-wide sampling without depending on order of
// initialization of static storage duration objects.
// The definition of this constant is weak, which allows us to inject a
// different value for it at link time.
extern "C" bool ABSL_INTERNAL_C_SYMBOL(AbslContainerInternalSampleEverything)();

}  // namespace container_internal
ABSL_NAMESPACE_END
}  // namespace absl

#endif  // ABSL_CONTAINER_INTERNAL_HASHTABLEZ_SAMPLER_H_
chromium/third_party/abseil-cpp/absl/container/internal/hashtablez_sampler.h
