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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/strings/internal/cordz_functions.h"
#include <thread> // NOLINT we need real clean new threads
#include "gmock/gmock.h"
#include "gtest/gtest.h"
#include "absl/base/config.h"
namespace absl {
ABSL_NAMESPACE_BEGIN
namespace cord_internal {
namespace {
using ::testing::Eq;
using ::testing::Ge;
using ::testing::Le;
TEST(CordzFunctionsTest, SampleRate) {
int32_t orig_sample_rate = get_cordz_mean_interval();
int32_t expected_sample_rate = 123;
set_cordz_mean_interval(expected_sample_rate);
EXPECT_THAT(get_cordz_mean_interval(), Eq(expected_sample_rate));
set_cordz_mean_interval(orig_sample_rate);
}
// Cordz is disabled when we don't have thread_local. All calls to
// should_profile will return false when cordz is disabled, so we might want to
// avoid those tests.
#ifdef ABSL_INTERNAL_CORDZ_ENABLED
TEST(CordzFunctionsTest, ShouldProfileDisable) {
int32_t orig_sample_rate = get_cordz_mean_interval();
set_cordz_mean_interval(0);
cordz_set_next_sample_for_testing(0);
EXPECT_FALSE(cordz_should_profile());
// 1 << 16 is from kIntervalIfDisabled in cordz_functions.cc.
EXPECT_THAT(cordz_next_sample, Eq(1 << 16));
set_cordz_mean_interval(orig_sample_rate);
}
TEST(CordzFunctionsTest, ShouldProfileAlways) {
int32_t orig_sample_rate = get_cordz_mean_interval();
set_cordz_mean_interval(1);
cordz_set_next_sample_for_testing(1);
EXPECT_TRUE(cordz_should_profile());
EXPECT_THAT(cordz_next_sample, Le(1));
set_cordz_mean_interval(orig_sample_rate);
}
TEST(CordzFunctionsTest, DoesNotAlwaysSampleFirstCord) {
// Set large enough interval such that the chance of 'tons' of threads
// randomly sampling the first call is infinitely small.
set_cordz_mean_interval(10000);
int tries = 0;
bool sampled = false;
do {
++tries;
ASSERT_THAT(tries, Le(1000));
std::thread thread([&sampled] {
sampled = cordz_should_profile();
});
thread.join();
} while (sampled);
}
TEST(CordzFunctionsTest, ShouldProfileRate) {
static constexpr int kDesiredMeanInterval = 1000;
static constexpr int kSamples = 10000;
int32_t orig_sample_rate = get_cordz_mean_interval();
set_cordz_mean_interval(kDesiredMeanInterval);
int64_t sum_of_intervals = 0;
for (int i = 0; i < kSamples; i++) {
// Setting next_sample to 0 will force cordz_should_profile to generate a
// new value for next_sample each iteration.
cordz_set_next_sample_for_testing(0);
cordz_should_profile();
sum_of_intervals += cordz_next_sample;
}
// The sum of independent exponential variables is an Erlang distribution,
// which is a gamma distribution where the shape parameter is equal to the
// number of summands. The distribution used for cordz_should_profile is
// actually floor(Exponential(1/mean)) which introduces bias. However, we can
// apply the squint-really-hard correction factor. That is, when mean is
// large, then if we squint really hard the shape of the distribution between
// N and N+1 looks like a uniform distribution. On average, each value for
// next_sample will be about 0.5 lower than we would expect from an
// exponential distribution. This squint-really-hard correction approach won't
// work when mean is smaller than about 10 but works fine when mean is 1000.
//
// We can use R to calculate a confidence interval. This
// shows how to generate a confidence interval with a false positive rate of
// one in a billion.
//
// $ R -q
// > mean = 1000
// > kSamples = 10000
// > errorRate = 1e-9
// > correction = -kSamples / 2
// > low = qgamma(errorRate/2, kSamples, 1/mean) + correction
// > high = qgamma(1 - errorRate/2, kSamples, 1/mean) + correction
// > low
// [1] 9396115
// > high
// [1] 10618100
EXPECT_THAT(sum_of_intervals, Ge(9396115));
EXPECT_THAT(sum_of_intervals, Le(10618100));
set_cordz_mean_interval(orig_sample_rate);
}
#else // ABSL_INTERNAL_CORDZ_ENABLED
TEST(CordzFunctionsTest, ShouldProfileDisabled) {
int32_t orig_sample_rate = get_cordz_mean_interval();
set_cordz_mean_interval(1);
cordz_set_next_sample_for_testing(0);
EXPECT_FALSE(cordz_should_profile());
set_cordz_mean_interval(orig_sample_rate);
}
#endif // ABSL_INTERNAL_CORDZ_ENABLED
} // namespace
} // namespace cord_internal
ABSL_NAMESPACE_END
} // namespace absl
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