Abseil Common Libraries (C++) (grcp 依赖) https://abseil.io/
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Export of internal Abseil changes -- f012012ef78234a6a4585321b67d7b7c92ebc266 by Laramie Leavitt <lar@google.com>: Slight restructuring of absl/random/internal randen implementation. Convert round-keys.inc into randen_round_keys.cc file. Consistently use a 128-bit pointer type for internal method parameters. This allows simpler pointer arithmetic in C++ & permits removal of some constants and casts. Remove some redundancy in comments & constexpr variables. Specifically, all references to Randen algorithm parameters use RandenTraits; duplication in RandenSlow removed. PiperOrigin-RevId: 312190313 -- dc8b42e054046741e9ed65335bfdface997c6063 by Abseil Team <absl-team@google.com>: Internal change. PiperOrigin-RevId: 312167304 -- f13d248fafaf206492c1362c3574031aea3abaf7 by Matthew Brown <matthewbr@google.com>: Cleanup StrFormat extensions a little. PiperOrigin-RevId: 312166336 -- 9d9117589667afe2332bb7ad42bc967ca7c54502 by Derek Mauro <dmauro@google.com>: Internal change PiperOrigin-RevId: 312105213 -- 9a12b9b3aa0e59b8ee6cf9408ed0029045543a9b by Abseil Team <absl-team@google.com>: Complete IGNORE_TYPE macro renaming. PiperOrigin-RevId: 311999699 -- 64756f20d61021d999bd0d4c15e9ad3857382f57 by Gennadiy Rozental <rogeeff@google.com>: Switch to fixed bytes specific default value. This fixes the Abseil Flags for big endian platforms. PiperOrigin-RevId: 311844448 -- bdbe6b5b29791dbc3816ada1828458b3010ff1e9 by Laramie Leavitt <lar@google.com>: Change many distribution tests to use pcg_engine as a deterministic source of entropy. It's reasonable to test that the BitGen itself has good entropy, however when testing the cross product of all random distributions x all the architecture variations x all submitted changes results in a large number of tests. In order to account for these failures while still using good entropy requires that our allowed sigma need to account for all of these independent tests. Our current sigma values are too restrictive, and we see a lot of failures, so we have to either relax the sigma values or convert some of the statistical tests to use deterministic values. This changelist does the latter. PiperOrigin-RevId: 311840096 GitOrigin-RevId: f012012ef78234a6a4585321b67d7b7c92ebc266 Change-Id: Ic84886f38ff30d7d72c126e9b63c9a61eb729a1a
5 years ago
// 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);
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