tvl-depot/absl/container/internal/hashtablez_sampler.cc

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Export of internal Abseil changes. -- 7fa1107161a03dac53fb84c2b06d8092616c7b13 by Abseil Team <absl-team@google.com>: Harden the generic stacktrace implementation for use during early program execution PiperOrigin-RevId: 226375950 -- 079f9969329f5eb66f647dd3c44b17541b1bf217 by Matt Kulukundis <kfm@google.com>: Workaround platforms that have over-aggressive warnings on -Wexit-time-destructors PiperOrigin-RevId: 226362948 -- 1447943f509be681ca5495add0162c750ef237f1 by Matt Kulukundis <kfm@google.com>: Switch from 64 to size_t atomics so they work on embedded platforms that do not have 64 bit atomics. PiperOrigin-RevId: 226210704 -- d14d49837ae2bcde74051e0c79c18ee0f43866b9 by Tom Manshreck <shreck@google.com>: Develop initial documentation for API breaking changes process: PiperOrigin-RevId: 226210021 -- 7ea3d7fe0e86979dab83a5fc9cc3bf1d6cb3bd53 by Abseil Team <absl-team@google.com>: Import of CCTZ from GitHub. PiperOrigin-RevId: 226195522 -- 7de873e880d7f016a4fa1e08d626f0535cc470af by Abseil Team <absl-team@google.com>: Make Abseil LICENSE files newline terminated, with a single trailing blank line. Also remove line-ending whitespace. PiperOrigin-RevId: 226182949 -- 7d00643fadfad7f0d992c68bd9d2ed2e5bc960b0 by Matt Kulukundis <kfm@google.com>: Internal cleanup PiperOrigin-RevId: 226045282 -- c4a0a11c0ce2875271191e477f3d36eaaeca4613 by Matt Kulukundis <kfm@google.com>: Internal cleanup PiperOrigin-RevId: 226038273 -- 8ee4ebbb1ae5cda119e436e5ff7e3aa966608c10 by Matt Kulukundis <kfm@google.com>: Adds a global sampler which tracks a fraction of live tables for collecting telemetry data. PiperOrigin-RevId: 226032080 -- d576446f050518cd1b0ae447d682d8552f0e7e30 by Mark Barolak <mbar@google.com>: Replace an internal CaseEqual function with calls to the identical absl::EqualsIgnoreCase. This closes out a rather old TODO. PiperOrigin-RevId: 226024779 -- 6b23f1ee028a5ffa608c920424f1220a117a8f3d by Abseil Team <absl-team@google.com>: Add December 2018 LTS branch to list of LTS branches. PiperOrigin-RevId: 226011333 -- bb0833a43bdaef4c8c059b17bcd27ba9a085a114 by Mark Barolak <mbar@google.com>: Explicitly state that when the SimpleAtoi family of functions encounter an error, the value of their output parameter is unspecified. Also standardize the name of the output parameter to be `out`. PiperOrigin-RevId: 225997035 -- 46c1876b1a248eabda7545daa61a74a4cdfe9077 by Abseil Team <absl-team@google.com>: Remove deprecated CMake function absl_test, absl_library and absl_header_library PiperOrigin-RevId: 225950041 GitOrigin-RevId: 7fa1107161a03dac53fb84c2b06d8092616c7b13 Change-Id: I2ca9d3aada9292614527d1339a7557494139b806
2018-12-20 21:29:59 +01:00
// 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
//
// http://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>
Export of internal Abseil changes. -- 7fa1107161a03dac53fb84c2b06d8092616c7b13 by Abseil Team <absl-team@google.com>: Harden the generic stacktrace implementation for use during early program execution PiperOrigin-RevId: 226375950 -- 079f9969329f5eb66f647dd3c44b17541b1bf217 by Matt Kulukundis <kfm@google.com>: Workaround platforms that have over-aggressive warnings on -Wexit-time-destructors PiperOrigin-RevId: 226362948 -- 1447943f509be681ca5495add0162c750ef237f1 by Matt Kulukundis <kfm@google.com>: Switch from 64 to size_t atomics so they work on embedded platforms that do not have 64 bit atomics. PiperOrigin-RevId: 226210704 -- d14d49837ae2bcde74051e0c79c18ee0f43866b9 by Tom Manshreck <shreck@google.com>: Develop initial documentation for API breaking changes process: PiperOrigin-RevId: 226210021 -- 7ea3d7fe0e86979dab83a5fc9cc3bf1d6cb3bd53 by Abseil Team <absl-team@google.com>: Import of CCTZ from GitHub. PiperOrigin-RevId: 226195522 -- 7de873e880d7f016a4fa1e08d626f0535cc470af by Abseil Team <absl-team@google.com>: Make Abseil LICENSE files newline terminated, with a single trailing blank line. Also remove line-ending whitespace. PiperOrigin-RevId: 226182949 -- 7d00643fadfad7f0d992c68bd9d2ed2e5bc960b0 by Matt Kulukundis <kfm@google.com>: Internal cleanup PiperOrigin-RevId: 226045282 -- c4a0a11c0ce2875271191e477f3d36eaaeca4613 by Matt Kulukundis <kfm@google.com>: Internal cleanup PiperOrigin-RevId: 226038273 -- 8ee4ebbb1ae5cda119e436e5ff7e3aa966608c10 by Matt Kulukundis <kfm@google.com>: Adds a global sampler which tracks a fraction of live tables for collecting telemetry data. PiperOrigin-RevId: 226032080 -- d576446f050518cd1b0ae447d682d8552f0e7e30 by Mark Barolak <mbar@google.com>: Replace an internal CaseEqual function with calls to the identical absl::EqualsIgnoreCase. This closes out a rather old TODO. PiperOrigin-RevId: 226024779 -- 6b23f1ee028a5ffa608c920424f1220a117a8f3d by Abseil Team <absl-team@google.com>: Add December 2018 LTS branch to list of LTS branches. PiperOrigin-RevId: 226011333 -- bb0833a43bdaef4c8c059b17bcd27ba9a085a114 by Mark Barolak <mbar@google.com>: Explicitly state that when the SimpleAtoi family of functions encounter an error, the value of their output parameter is unspecified. Also standardize the name of the output parameter to be `out`. PiperOrigin-RevId: 225997035 -- 46c1876b1a248eabda7545daa61a74a4cdfe9077 by Abseil Team <absl-team@google.com>: Remove deprecated CMake function absl_test, absl_library and absl_header_library PiperOrigin-RevId: 225950041 GitOrigin-RevId: 7fa1107161a03dac53fb84c2b06d8092616c7b13 Change-Id: I2ca9d3aada9292614527d1339a7557494139b806
2018-12-20 21:29:59 +01:00
#include <functional>
#include <limits>
#include "absl/base/attributes.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 {
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};
// Returns the next pseudo-random value.
// pRNG is: aX+b mod c with a = 0x5DEECE66D, b = 0xB, c = 1<<48
// This is the lrand64 generator.
uint64_t NextRandom(uint64_t rnd) {
const uint64_t prng_mult = uint64_t{0x5DEECE66D};
const uint64_t prng_add = 0xB;
const uint64_t prng_mod_power = 48;
const uint64_t prng_mod_mask = ~(~uint64_t{0} << prng_mod_power);
return (prng_mult * rnd + prng_add) & prng_mod_mask;
}
// Generates a geometric variable with the specified mean.
// This is done by generating a random number between 0 and 1 and applying
// the inverse cumulative distribution function for an exponential.
// Specifically: Let m be the inverse of the sample period, then
// the probability distribution function is m*exp(-mx) so the CDF is
// p = 1 - exp(-mx), so
// q = 1 - p = exp(-mx)
// log_e(q) = -mx
// -log_e(q)/m = x
// log_2(q) * (-log_e(2) * 1/m) = x
// In the code, q is actually in the range 1 to 2**26, hence the -26 below
//
int64_t GetGeometricVariable(int64_t mean) {
#if ABSL_HAVE_THREAD_LOCAL
thread_local
#else // ABSL_HAVE_THREAD_LOCAL
// SampleSlow and hence GetGeometricVariable is guarded by a single mutex when
// there are not thread locals. Thus, a single global rng is acceptable for
// that case.
static
#endif // ABSL_HAVE_THREAD_LOCAL
uint64_t rng = []() {
// We don't get well distributed numbers from this so we call
// NextRandom() a bunch to mush the bits around. We use a global_rand
// to handle the case where the same thread (by memory address) gets
// created and destroyed repeatedly.
ABSL_CONST_INIT static std::atomic<uint32_t> global_rand(0);
uint64_t r = reinterpret_cast<uint64_t>(&rng) +
global_rand.fetch_add(1, std::memory_order_relaxed);
for (int i = 0; i < 20; ++i) {
r = NextRandom(r);
}
return r;
}();
rng = NextRandom(rng);
// Take the top 26 bits as the random number
// (This plus the 1<<58 sampling bound give a max possible step of
// 5194297183973780480 bytes.)
const uint64_t prng_mod_power = 48; // Number of bits in prng
// The uint32_t cast is to prevent a (hard-to-reproduce) NAN
// under piii debug for some binaries.
double q = static_cast<uint32_t>(rng >> (prng_mod_power - 26)) + 1.0;
// Put the computed p-value through the CDF of a geometric.
double interval = (std::log2(q) - 26) * (-std::log(2.0) * mean);
// Very large values of interval overflow int64_t. If we happen to
// hit such improbable condition, we simply cheat and clamp interval
// to largest supported value.
if (interval > static_cast<double>(std::numeric_limits<int64_t>::max() / 2)) {
return std::numeric_limits<int64_t>::max() / 2;
}
// Small values of interval are equivalent to just sampling next time.
if (interval < 1) {
return 1;
}
return static_cast<int64_t>(interval);
}
} // namespace
HashtablezSampler& HashtablezSampler::Global() {
static auto* sampler = new HashtablezSampler();
return *sampler;
}
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) {
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) {
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);
}
HashtablezInfo* SampleSlow(int64_t* next_sample) {
bool first = *next_sample < 0;
*next_sample = GetGeometricVariable(
g_hashtablez_sample_parameter.load(std::memory_order_relaxed));
// 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();
}
Export of internal Abseil changes. -- 5f1cf6547231f1b1daad6d1b785df6b0b999b3c9 by Samuel Benzaquen <sbenza@google.com>: Fix uninitialized member in the `iterator` class by using a union of the two possible states of the iterator. This silences a Wuninitialized warning in gcc>=7. PiperOrigin-RevId: 228175148 -- 98b4e3204c0ec3cfd4cb037e24d443ea4b63fc84 by CJ Johnson <johnsoncj@google.com>: Factors out the implementation of InlinedVector::swap(...) into a private member function PiperOrigin-RevId: 228173383 -- f1432ad3a8b05285c6d55bc4754cfae765485b7f by Abseil Team <absl-team@google.com>: Import of CCTZ from GitHub. PiperOrigin-RevId: 227891984 -- 03fc00c7a4efc6000e6d9125cb2e252bffda76fe by Andy Getzendanner <durandal@google.com>: Add a missing linebreak to a comment and markdownify two unordered lists. PiperOrigin-RevId: 227861389 -- 0d66c9afba4fc9aa52e61d9fb410e165018a7b48 by Abseil Team <absl-team@google.com>: Add an API to register a new source for the cycle clock. PiperOrigin-RevId: 227779218 -- 14d3f9b70c8818b8541e5fb2f6ca4c59d479de31 by Andy Getzendanner <durandal@google.com>: Correct a typo in a stripping marker. PiperOrigin-RevId: 227750014 -- 59df88740f4e315beb57a8772f8bcf7879440c74 by Matt Kulukundis <kfm@google.com>: Switch thread local handling to be more cross platform PiperOrigin-RevId: 227695133 -- 75deed5bfcb5c42534e933f104aa7d94e11e348d by Abseil Team <absl-team@google.com>: Rollback workaround toolchain bug for incorrect handling of thread_local in inline functions PiperOrigin-RevId: 227689133 -- 54994bf0afec026e6e0e7a199df0bbb4b7d9a4aa by Derek Mauro <dmauro@google.com>: Add -pthread to linkopts where it actually belongs, on the library that uses it. Fixes https://github.com/abseil/abseil-cpp/issues/240. PiperOrigin-RevId: 227612492 -- 893875f3536b7e0a1bad993aa6b2e083abb3b25a by Derek Mauro <dmauro@google.com>: Internal change PiperOrigin-RevId: 227582833 -- 506c9b8e9002ca3389c7040473b68d4cbf94bdcc by Matt Kulukundis <kfm@google.com>: Workaround toolchain bug for incorrect handling of thread_local in inline functions PiperOrigin-RevId: 227561449 -- 29ee90d96dfe3114cf93f9bb92ea0cc9e768a407 by Derek Mauro <dmauro@google.com>: Internal change PiperOrigin-RevId: 227054634 GitOrigin-RevId: 5f1cf6547231f1b1daad6d1b785df6b0b999b3c9 Change-Id: Ibc90566d92ee6e0ad7e150f513ec7f5d22ec0a94
2019-01-07 18:01:16 +01:00
#if ABSL_PER_THREAD_TLS == 1
ABSL_PER_THREAD_TLS_KEYWORD int64_t next_sample = 0;
#endif // ABSL_PER_THREAD_TLS == 1
Export of internal Abseil changes. -- 7fa1107161a03dac53fb84c2b06d8092616c7b13 by Abseil Team <absl-team@google.com>: Harden the generic stacktrace implementation for use during early program execution PiperOrigin-RevId: 226375950 -- 079f9969329f5eb66f647dd3c44b17541b1bf217 by Matt Kulukundis <kfm@google.com>: Workaround platforms that have over-aggressive warnings on -Wexit-time-destructors PiperOrigin-RevId: 226362948 -- 1447943f509be681ca5495add0162c750ef237f1 by Matt Kulukundis <kfm@google.com>: Switch from 64 to size_t atomics so they work on embedded platforms that do not have 64 bit atomics. PiperOrigin-RevId: 226210704 -- d14d49837ae2bcde74051e0c79c18ee0f43866b9 by Tom Manshreck <shreck@google.com>: Develop initial documentation for API breaking changes process: PiperOrigin-RevId: 226210021 -- 7ea3d7fe0e86979dab83a5fc9cc3bf1d6cb3bd53 by Abseil Team <absl-team@google.com>: Import of CCTZ from GitHub. PiperOrigin-RevId: 226195522 -- 7de873e880d7f016a4fa1e08d626f0535cc470af by Abseil Team <absl-team@google.com>: Make Abseil LICENSE files newline terminated, with a single trailing blank line. Also remove line-ending whitespace. PiperOrigin-RevId: 226182949 -- 7d00643fadfad7f0d992c68bd9d2ed2e5bc960b0 by Matt Kulukundis <kfm@google.com>: Internal cleanup PiperOrigin-RevId: 226045282 -- c4a0a11c0ce2875271191e477f3d36eaaeca4613 by Matt Kulukundis <kfm@google.com>: Internal cleanup PiperOrigin-RevId: 226038273 -- 8ee4ebbb1ae5cda119e436e5ff7e3aa966608c10 by Matt Kulukundis <kfm@google.com>: Adds a global sampler which tracks a fraction of live tables for collecting telemetry data. PiperOrigin-RevId: 226032080 -- d576446f050518cd1b0ae447d682d8552f0e7e30 by Mark Barolak <mbar@google.com>: Replace an internal CaseEqual function with calls to the identical absl::EqualsIgnoreCase. This closes out a rather old TODO. PiperOrigin-RevId: 226024779 -- 6b23f1ee028a5ffa608c920424f1220a117a8f3d by Abseil Team <absl-team@google.com>: Add December 2018 LTS branch to list of LTS branches. PiperOrigin-RevId: 226011333 -- bb0833a43bdaef4c8c059b17bcd27ba9a085a114 by Mark Barolak <mbar@google.com>: Explicitly state that when the SimpleAtoi family of functions encounter an error, the value of their output parameter is unspecified. Also standardize the name of the output parameter to be `out`. PiperOrigin-RevId: 225997035 -- 46c1876b1a248eabda7545daa61a74a4cdfe9077 by Abseil Team <absl-team@google.com>: Remove deprecated CMake function absl_test, absl_library and absl_header_library PiperOrigin-RevId: 225950041 GitOrigin-RevId: 7fa1107161a03dac53fb84c2b06d8092616c7b13 Change-Id: I2ca9d3aada9292614527d1339a7557494139b806
2018-12-20 21:29:59 +01:00
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 SWISSTABLE_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
} // namespace absl