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Diffstat (limited to 'absl/strings/internal/cordz_functions_test.cc')
-rw-r--r-- | absl/strings/internal/cordz_functions_test.cc | 131 |
1 files changed, 131 insertions, 0 deletions
diff --git a/absl/strings/internal/cordz_functions_test.cc b/absl/strings/internal/cordz_functions_test.cc new file mode 100644 index 00000000..f2cefae3 --- /dev/null +++ b/absl/strings/internal/cordz_functions_test.cc @@ -0,0 +1,131 @@ +// 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 "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 diabled, 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, 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 |