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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 "y_absl/strings/internal/cordz_functions.h"
#include <atomic>
#include <cmath>
#include <limits>
#include <random>
#include "y_absl/base/attributes.h"
#include "y_absl/base/config.h"
#include "y_absl/base/internal/raw_logging.h"
#include "y_absl/profiling/internal/exponential_biased.h"
namespace y_absl {
Y_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 Y_ABSL_INTERNAL_CORDZ_ENABLED
// Special negative 'not initialized' per thread value for cordz_next_sample.
static constexpr int64_t kInitCordzNextSample = -1;
Y_ABSL_CONST_INIT thread_local SamplingState cordz_next_sample = {
kInitCordzNextSample, 1};
// 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;
Y_ABSL_ATTRIBUTE_NOINLINE int64_t
cordz_should_profile_slow(SamplingState& state) {
thread_local y_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) {
state = {kIntervalIfDisabled, kIntervalIfDisabled};
return 0;
}
// Check if we're always sampling.
if (mean_interval == 1) {
state = {1, 1};
return 1;
}
if (cordz_next_sample.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.next_sample != kInitCordzNextSample;
auto old_stride = state.sample_stride;
auto stride = exponential_biased_generator.GetStride(mean_interval);
state = {stride, stride};
bool should_sample = initialized || cordz_should_profile() > 0;
return should_sample ? old_stride : 0;
}
--state.next_sample;
return 0;
}
void cordz_set_next_sample_for_testing(int64_t next_sample) {
cordz_next_sample = {next_sample, next_sample};
}
#endif // Y_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
Y_ABSL_NAMESPACE_END
} // namespace y_absl
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