diff options
Diffstat (limited to 'third_party/abseil-cpp/absl/strings/internal/cordz_functions.cc')
-rw-r--r-- | third_party/abseil-cpp/absl/strings/internal/cordz_functions.cc | 96 |
1 files changed, 96 insertions, 0 deletions
diff --git a/third_party/abseil-cpp/absl/strings/internal/cordz_functions.cc b/third_party/abseil-cpp/absl/strings/internal/cordz_functions.cc new file mode 100644 index 0000000000..20d314f03c --- /dev/null +++ b/third_party/abseil-cpp/absl/strings/internal/cordz_functions.cc @@ -0,0 +1,96 @@ +// 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 <atomic> +#include <cmath> +#include <limits> +#include <random> + +#include "absl/base/attributes.h" +#include "absl/base/config.h" +#include "absl/base/internal/raw_logging.h" +#include "absl/profiling/internal/exponential_biased.h" + +namespace absl { +ABSL_NAMESPACE_BEGIN +namespace cord_internal { +namespace { + +// The average interval until the next sample. A value of 0 disables profiling +// while a value of 1 will profile all Cords. +std::atomic<int> g_cordz_mean_interval(50000); + +} // namespace + +#ifdef ABSL_INTERNAL_CORDZ_ENABLED + +// Special negative 'not initialized' per thread value for cordz_next_sample. +static constexpr int64_t kInitCordzNextSample = -1; + +ABSL_CONST_INIT thread_local int64_t cordz_next_sample = kInitCordzNextSample; + +// kIntervalIfDisabled is the number of profile-eligible events need to occur +// before the code will confirm that cordz is still disabled. +constexpr int64_t kIntervalIfDisabled = 1 << 16; + +ABSL_ATTRIBUTE_NOINLINE bool cordz_should_profile_slow() { + + thread_local absl::profiling_internal::ExponentialBiased + exponential_biased_generator; + int32_t mean_interval = get_cordz_mean_interval(); + + // Check if we disabled profiling. If so, set the next sample to a "large" + // number to minimize the overhead of the should_profile codepath. + if (mean_interval <= 0) { + cordz_next_sample = kIntervalIfDisabled; + return false; + } + + // Check if we're always sampling. + if (mean_interval == 1) { + cordz_next_sample = 1; + return true; + } + + if (cordz_next_sample <= 0) { + // If first check on current thread, check cordz_should_profile() + // again using the created (initial) stride in cordz_next_sample. + const bool initialized = cordz_next_sample != kInitCordzNextSample; + cordz_next_sample = exponential_biased_generator.GetStride(mean_interval); + return initialized || cordz_should_profile(); + } + + --cordz_next_sample; + return false; +} + +void cordz_set_next_sample_for_testing(int64_t next_sample) { + cordz_next_sample = next_sample; +} + +#endif // ABSL_INTERNAL_CORDZ_ENABLED + +int32_t get_cordz_mean_interval() { + return g_cordz_mean_interval.load(std::memory_order_acquire); +} + +void set_cordz_mean_interval(int32_t mean_interval) { + g_cordz_mean_interval.store(mean_interval, std::memory_order_release); +} + +} // namespace cord_internal +ABSL_NAMESPACE_END +} // namespace absl |