From aa844899c937bde5d2b24f276b59997e5b668bde Mon Sep 17 00:00:00 2001 From: Abseil Team Date: Thu, 8 Aug 2019 10:56:58 -0700 Subject: Creation of LTS branch "lts_2019_08_08" - 9ee91d3e430fb33a4590486573792eb0fa146c2d Export of internal Abseil changes by Abseil Team - 8efba58a3b656e9b41fb0471ae6453425a61c520 Export of internal Abseil changes by Abseil Team - b49b8d16b67ec6912899684b732e6367f258cfdb Export of internal Abseil changes by Abseil Team - 67222ffc4c83d918ce8395aa61769eeb77df4c4d Export of internal Abseil changes by Abseil Team - c5c4db4f5191fe5e76cbf68dcc71fb28702f7d2b Export of internal Abseil changes by Abseil Team - 14550beb3b7b97195e483fb74b5efb906395c31e Export of internal Abseil changes. by Abseil Team - 52e88ee56b72cf32bc66534d942c7398ce481331 Export of internal Abseil changes. by Abseil Team - 36d37ab992038f52276ca66b9da80c1cf0f57dc2 Export of internal Abseil changes. by Abseil Team - ad1485c8986246b2ae9105e512738d0e97aec887 Export of internal Abseil changes. by Abseil Team - 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968a34ffdaadd7db062a9621dfbdf8b2d16e05af Export of internal Abseil changes. by Abseil Team - 3e2e9b5557e76d098de4b8a2a659125b98ca519b Merge pull request #231 from uilianries/feature/conan by Mark Barolak - 111ca7060a6ff50115ca85b59f6b5d8c8c5e9105 Export of internal Abseil changes. by Abseil Team - 389ec3f906f018661a5308458d623d01f96d7b23 Export of internal Abseil changes. by Abseil Team - 8fbcdb90952c57828c4a9c2f6d79fcd7cae9088f Export of internal Abseil changes. by Abseil Team - 455dc17ba1af9635f0b60155bc565bc572a1e722 Export of internal Abseil changes. by Abseil Team - f197d7c72a54064cfde5a2058f1513a4a0ee36fb Export of internal Abseil changes. by Abseil Team - 284378a71b32dfb3af4e3661f585e671d1b603a3 Export of internal Abseil changes. by Abseil Team GitOrigin-RevId: 9ee91d3e430fb33a4590486573792eb0fa146c2d Change-Id: Ia06e548bc106cc9d136f6c65714be6645317aced --- absl/container/internal/hashtablez_sampler.cc | 310 ++++++++++++++++++++++++++ 1 file changed, 310 insertions(+) create mode 100644 absl/container/internal/hashtablez_sampler.cc (limited to 'absl/container/internal/hashtablez_sampler.cc') diff --git a/absl/container/internal/hashtablez_sampler.cc b/absl/container/internal/hashtablez_sampler.cc new file mode 100644 index 00000000..2338045d --- /dev/null +++ b/absl/container/internal/hashtablez_sampler.cc @@ -0,0 +1,310 @@ +// 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 +#include +#include +#include +#include + +#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 { +inline namespace lts_2019_08_08 { +namespace container_internal { +constexpr int HashtablezInfo::kMaxStackDepth; + +namespace { +ABSL_CONST_INIT std::atomic g_hashtablez_enabled{ + false +}; +ABSL_CONST_INIT std::atomic g_hashtablez_sample_parameter{1 << 10}; +ABSL_CONST_INIT std::atomic 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 global_rand(0); + uint64_t r = reinterpret_cast(&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(rng >> (prng_mod_power - 26)) + 1.0; + // Put the computed p-value through the CDF of a geometric. + double interval = (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(std::numeric_limits::max() / 2)) { + return std::numeric_limits::max() / 2; + } + + // Small values of interval are equivalent to just sampling next time. + if (interval < 1) { + return 1; + } + return static_cast(interval); +} + +} // namespace + +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& 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) { + if (kAbslContainerInternalSampleEverything) { + *next_sample = 1; + return HashtablezSampler::Global().Register(); + } + + 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(); +} + +#if ABSL_PER_THREAD_TLS == 1 +ABSL_PER_THREAD_TLS_KEYWORD int64_t global_next_sample = 0; +#endif // ABSL_PER_THREAD_TLS == 1 + +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(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(max)); // NOLINT(runtime/int) + } +} + +} // namespace container_internal +} // inline namespace lts_2019_08_08 +} // namespace absl -- cgit v1.2.3