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Export of internal Abseil changes

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3a871e2cd854a46770a9416189953b2b38980bcf by Andy Getzendanner <durandal@google.com>:

Import of CCTZ from GitHub.

PiperOrigin-RevId: 280660534

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f5a155fb056dcf68b089c21aebb5bf5159dc0eb3 by Tom Manshreck <shreck@google.com>:

Nit: fix format of algorithm.h comments

PiperOrigin-RevId: 280474139

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08b117a18353c0daf51b33b45100e5a007e5ab0c by Abseil Team <absl-team@google.com>:

Allow absl::Notification::HasBeenNotified to be inlined.

PiperOrigin-RevId: 280453271

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26d33dd2bad72945f1987f7b2669dbec3a6247e6 by Derek Mauro <dmauro@google.com>:

Fix unused variable warnings on Windows

PiperOrigin-RevId: 280324417

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907e9b23029be683af3b443bafd6a577a595922f by Abseil Team <absl-team@google.com>:

PeriodicSampler implementation (for internal-use only)

PiperOrigin-RevId: 280257168
GitOrigin-RevId: 3a871e2cd854a46770a9416189953b2b38980bcf
Change-Id: I6e2978cae22a6adc41c0577e5c21355e9db7c8f5
This commit is contained in:
Abseil Team 2019-11-15 08:07:12 -08:00 • committed by Andy Getz
parent fa8c75182f
commit 3df7b52a6a
12 changed files with 581 additions and 19 deletions
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50
absl/base/internal/periodic_sampler.cc Normal file
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// Copyright 2019 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/base/internal/periodic_sampler.h"
#include <atomic>
#include "absl/base/internal/exponential_biased.h"
namespace absl {
namespace base_internal {
int64_t PeriodicSamplerBase::GetExponentialBiased(int period) noexcept {
return rng_.Get(period);
}
bool PeriodicSamplerBase::SubtleConfirmSample() noexcept {
int current_period = period();
// Deal with period case 0 (always off) and 1 (always on)
if (ABSL_PREDICT_FALSE(current_period < 2)) {
stride_ = 0;
return current_period == 1;
}
// Check if this is the first call to Sample()
if (ABSL_PREDICT_FALSE(stride_ == 1)) {
stride_ = -1 - GetExponentialBiased(current_period);
if (stride_ < -1) {
++stride_;
return false;
}
}
stride_ = -1 - GetExponentialBiased(current_period);
return true;
}
} // namespace base_internal
} // namespace absl

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absl/base/internal/periodic_sampler.h Normal file
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// Copyright 2019 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.
#ifndef ABSL_BASE_INTERNAL_PERIODIC_SAMPLER_H_
#define ABSL_BASE_INTERNAL_PERIODIC_SAMPLER_H_
#include <stdint.h>
#include <atomic>
#include "absl/base/internal/exponential_biased.h"
#include "absl/base/optimization.h"
namespace absl {
namespace base_internal {
// PeriodicSamplerBase provides the basic period sampler implementation.
//
// This is the base class for the templated PeriodicSampler class, which holds
// a global std::atomic value identified by a user defined tag, such that
// each specific PeriodSampler implementation holds its own global period.
//
// PeriodicSamplerBase is thread-compatible except where stated otherwise.
class PeriodicSamplerBase {
public:
// PeriodicSamplerBase is trivial / copyable / movable / destructible.
PeriodicSamplerBase() = default;
PeriodicSamplerBase(PeriodicSamplerBase&&) = default;
PeriodicSamplerBase(const PeriodicSamplerBase&) = default;
// Returns true roughly once every `period` calls. This is established by a
// randomly picked `stride` that is counted down on each call to `Sample`.
// This stride is picked such that the probability of `Sample()` returning
// true is 1 in `period`.
inline bool Sample() noexcept;
// The below methods are intended for optimized use cases where the
// size of the inlined fast path code is highly important. Applications
// should use the `Sample()` method unless they have proof that their
// specific use case requires the optimizations offered by these methods.
//
// An example of such a use case is SwissTable sampling. All sampling checks
// are in inlined SwissTable methods, and the number of call sites is huge.
// In this case, the inlined code size added to each translation unit calling
// SwissTable methods is non-trivial.
//
// The `SubtleMaybeSample()` function spuriously returns true even if the
// function should not be sampled, applications MUST match each call to
// 'SubtleMaybeSample()' returning true with a `SubtleConfirmSample()` call,
// and use the result of the latter as the sampling decision.
// In other words: the code should logically be equivalent to:
//
// if (SubtleMaybeSample() && SubtleConfirmSample()) {
// // Sample this call
// }
//
// In the 'inline-size' optimized case, the `SubtleConfirmSample()` call can
// be placed out of line, for example, the typical use case looks as follows:
//
// // --- frobber.h -----------
// void FrobberSampled();
//
// inline void FrobberImpl() {
// // ...
// }
//
// inline void Frobber() {
// if (ABSL_PREDICT_FALSE(sampler.SubtleMaybeSample())) {
// FrobberSampled();
// } else {
// FrobberImpl();
// }
// }
//
// // --- frobber.cc -----------
// void FrobberSampled() {
// if (!sampler.SubtleConfirmSample())) {
// // Spurious false positive
// FrobberImpl();
// return;
// }
//
// // Sampled execution
// // ...
// }
inline bool SubtleMaybeSample() noexcept;
bool SubtleConfirmSample() noexcept;
protected:
// We explicitly don't use a virtual destructor as this class is never
// virtually destroyed, and it keeps the class trivial, which avoids TLS
// prologue and epilogue code for our TLS instances.
~PeriodicSamplerBase() = default;
// Returns the next stride for our sampler.
// This function is virtual for testing purposes only.
virtual int64_t GetExponentialBiased(int period) noexcept;
private:
// Returns the current period of this sampler. Thread-safe.
virtual int period() const noexcept = 0;
int64_t stride_ = 0;
ExponentialBiased rng_;
};
inline bool PeriodicSamplerBase::SubtleMaybeSample() noexcept {
// We explicitly count up and not down, as the compiler does not generate
// ideal code for counting down. See also https://gcc.godbolt.org/z/FTPDSM
//
// With `if (ABSL_PREDICT_FALSE(++stride_ < 0))`
// add QWORD PTR fs:sampler@tpoff+8, 1
// jns .L15
// ret
//
// With `if (ABSL_PREDICT_FALSE(--stride_ > 0))`
// mov rax, QWORD PTR fs:sampler@tpoff+8
// sub rax, 1
// mov QWORD PTR fs:sampler@tpoff+8, rax
// test rax, rax
// jle .L15
// ret
// add QWORD PTR fs:sampler@tpoff+8, 1
// jns .L15
// ret
//
// --stride >= 0 does work, but makes our logic slightly harder as in that
// case we have less convenient zero-init and over-run values.
if (ABSL_PREDICT_FALSE(++stride_ < 0)) {
return false;
}
return true;
}
inline bool PeriodicSamplerBase::Sample() noexcept {
return ABSL_PREDICT_FALSE(SubtleMaybeSample()) ? SubtleConfirmSample()
: false;
}
// PeriodicSampler is a concreted periodic sampler implementation.
// The user provided Tag identifies the implementation, and is required to
// isolate the global state of this instance from other instances.
//
// Typical use case:
//
// struct HashTablezTag {};
// thread_local PeriodicSampler sampler;
//
// void HashTableSamplingLogic(...) {
// if (sampler.Sample()) {
// HashTableSlowSamplePath(...);
// }
// }
//
template <typename Tag, int default_period = 0>
class PeriodicSampler final : public PeriodicSamplerBase {
public:
~PeriodicSampler() = default;
int period() const noexcept final {
return period_.load(std::memory_order_relaxed);
}
// Sets the global period for this sampler. Thread-safe.
// Setting a period of 0 disables the sampler, i.e., every call to Sample()
// will return false. Setting a period of 1 puts the sampler in 'always on'
// mode, i.e., every call to Sample() returns true.
static void SetGlobalPeriod(int period) {
period_.store(period, std::memory_order_relaxed);
}
private:
static std::atomic<int> period_;
};
template <typename Tag, int default_period>
std::atomic<int> PeriodicSampler<Tag, default_period>::period_(default_period);
} // namespace base_internal
} // namespace absl
#endif // ABSL_BASE_INTERNAL_PERIODIC_SAMPLER_H_

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// Copyright 2019 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 "benchmark/benchmark.h"
#include "absl/base/internal/periodic_sampler.h"
namespace absl {
namespace base_internal {
namespace {
template <typename Sampler>
void BM_Sample(Sampler* sampler, benchmark::State& state) {
for (auto _ : state) {
benchmark::DoNotOptimize(sampler);
benchmark::DoNotOptimize(sampler->Sample());
}
}
template <typename Sampler>
void BM_SampleMinunumInlined(Sampler* sampler, benchmark::State& state) {
for (auto _ : state) {
benchmark::DoNotOptimize(sampler);
if (ABSL_PREDICT_FALSE(sampler->SubtleMaybeSample())) {
benchmark::DoNotOptimize(sampler->SubtleConfirmSample());
}
}
}
void BM_PeriodicSampler_ShortSample(benchmark::State& state) {
struct Tag {};
PeriodicSampler<Tag, 1024> sampler;
BM_Sample(&sampler, state);
}
BENCHMARK(BM_PeriodicSampler_ShortSample);
void BM_PeriodicSampler_LongSample(benchmark::State& state) {
struct Tag {};
PeriodicSampler<Tag, 1024 * 1024> sampler;
BM_Sample(&sampler, state);
}
BENCHMARK(BM_PeriodicSampler_LongSample);
void BM_PeriodicSampler_LongSampleMinunumInlined(benchmark::State& state) {
struct Tag {};
PeriodicSampler<Tag, 1024 * 1024> sampler;
BM_SampleMinunumInlined(&sampler, state);
}
BENCHMARK(BM_PeriodicSampler_LongSampleMinunumInlined);
void BM_PeriodicSampler_Disabled(benchmark::State& state) {
struct Tag {};
PeriodicSampler<Tag, 0> sampler;
BM_Sample(&sampler, state);
}
BENCHMARK(BM_PeriodicSampler_Disabled);
} // namespace
} // namespace base_internal
} // namespace absl

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// Copyright 2019 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/base/internal/periodic_sampler.h"
#include <thread> // NOLINT(build/c++11)
#include "gmock/gmock.h"
#include "gtest/gtest.h"
#include "absl/base/attributes.h"
#include "absl/base/macros.h"
namespace absl {
namespace base_internal {
namespace {
using testing::Eq;
using testing::Return;
using testing::StrictMock;
class MockPeriodicSampler : public PeriodicSamplerBase {
public:
virtual ~MockPeriodicSampler() = default;
MOCK_METHOD(int, period, (), (const, noexcept));
MOCK_METHOD(int64_t, GetExponentialBiased, (int), (noexcept));
};
TEST(PeriodicSamplerBaseTest, Sample) {
StrictMock<MockPeriodicSampler> sampler;
EXPECT_CALL(sampler, period()).Times(3).WillRepeatedly(Return(16));
EXPECT_CALL(sampler, GetExponentialBiased(16))
.WillOnce(Return(1))
.WillOnce(Return(2))
.WillOnce(Return(3));
EXPECT_FALSE(sampler.Sample());
EXPECT_TRUE(sampler.Sample());
EXPECT_FALSE(sampler.Sample());
EXPECT_FALSE(sampler.Sample());
EXPECT_TRUE(sampler.Sample());
EXPECT_FALSE(sampler.Sample());
EXPECT_FALSE(sampler.Sample());
EXPECT_FALSE(sampler.Sample());
}
TEST(PeriodicSamplerBaseTest, ImmediatelySample) {
StrictMock<MockPeriodicSampler> sampler;
EXPECT_CALL(sampler, period()).Times(2).WillRepeatedly(Return(16));
EXPECT_CALL(sampler, GetExponentialBiased(16))
.WillOnce(Return(0))
.WillOnce(Return(1))
.WillOnce(Return(2));
EXPECT_TRUE(sampler.Sample());
EXPECT_FALSE(sampler.Sample());
EXPECT_TRUE(sampler.Sample());
EXPECT_FALSE(sampler.Sample());
EXPECT_FALSE(sampler.Sample());
}
TEST(PeriodicSamplerBaseTest, Disabled) {
StrictMock<MockPeriodicSampler> sampler;
EXPECT_CALL(sampler, period()).Times(3).WillRepeatedly(Return(0));
EXPECT_FALSE(sampler.Sample());
EXPECT_FALSE(sampler.Sample());
EXPECT_FALSE(sampler.Sample());
}
TEST(PeriodicSamplerBaseTest, AlwaysOn) {
StrictMock<MockPeriodicSampler> sampler;
EXPECT_CALL(sampler, period()).Times(3).WillRepeatedly(Return(1));
EXPECT_TRUE(sampler.Sample());
EXPECT_TRUE(sampler.Sample());
EXPECT_TRUE(sampler.Sample());
}
TEST(PeriodicSamplerBaseTest, Disable) {
StrictMock<MockPeriodicSampler> sampler;
EXPECT_CALL(sampler, period()).WillOnce(Return(16));
EXPECT_CALL(sampler, GetExponentialBiased(16)).WillOnce(Return(2));
EXPECT_FALSE(sampler.Sample());
EXPECT_FALSE(sampler.Sample());
EXPECT_CALL(sampler, period()).Times(2).WillRepeatedly(Return(0));
EXPECT_FALSE(sampler.Sample());
EXPECT_FALSE(sampler.Sample());
}
TEST(PeriodicSamplerBaseTest, Enable) {
StrictMock<MockPeriodicSampler> sampler;
EXPECT_CALL(sampler, period()).WillOnce(Return(0));
EXPECT_FALSE(sampler.Sample());
EXPECT_CALL(sampler, period()).Times(2).WillRepeatedly(Return(16));
EXPECT_CALL(sampler, GetExponentialBiased(16))
.Times(2)
.WillRepeatedly(Return(2));
EXPECT_FALSE(sampler.Sample());
EXPECT_FALSE(sampler.Sample());
EXPECT_TRUE(sampler.Sample());
EXPECT_FALSE(sampler.Sample());
EXPECT_FALSE(sampler.Sample());
}
TEST(PeriodicSamplerTest, ConstructConstInit) {
struct Tag {};
ABSL_CONST_INIT static PeriodicSampler<Tag> sampler;
(void)sampler;
}
TEST(PeriodicSamplerTest, DefaultPeriod0) {
struct Tag {};
PeriodicSampler<Tag> sampler;
EXPECT_THAT(sampler.period(), Eq(0));
}
TEST(PeriodicSamplerTest, DefaultPeriod) {
struct Tag {};
PeriodicSampler<Tag, 100> sampler;
EXPECT_THAT(sampler.period(), Eq(100));
}
TEST(PeriodicSamplerTest, SetGlobalPeriod) {
struct Tag1 {};
struct Tag2 {};
PeriodicSampler<Tag1, 25> sampler1;
PeriodicSampler<Tag2, 50> sampler2;
EXPECT_THAT(sampler1.period(), Eq(25));
EXPECT_THAT(sampler2.period(), Eq(50));
std::thread thread([] {
PeriodicSampler<Tag1, 25> sampler1;
PeriodicSampler<Tag2, 50> sampler2;
EXPECT_THAT(sampler1.period(), Eq(25));
EXPECT_THAT(sampler2.period(), Eq(50));
sampler1.SetGlobalPeriod(10);
sampler2.SetGlobalPeriod(20);
});
thread.join();
EXPECT_THAT(sampler1.period(), Eq(10));
EXPECT_THAT(sampler2.period(), Eq(20));
}
} // namespace
} // namespace base_internal
} // namespace absl