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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 <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
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