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// Copyright The OpenTelemetry Authors
// SPDX-License-Identifier: Apache-2.0
#include "src/common/random.h"
#include "src/common/platform/fork.h"
#include <atomic>
#include <cstring>
#include <random>
OPENTELEMETRY_BEGIN_NAMESPACE
namespace sdk
{
namespace common
{
// Wraps a thread_local random number generator, but adds a fork handler so that
// the generator will be correctly seeded after forking.
//
// See https://stackoverflow.com/q/51882689/4447365 and
// https://github.com/opentracing-contrib/nginx-opentracing/issues/52
namespace
{
class TlsRandomNumberGenerator
{
public:
TlsRandomNumberGenerator() noexcept
{
Seed();
if (!flag.test_and_set())
{
platform::AtFork(nullptr, nullptr, OnFork);
}
}
static FastRandomNumberGenerator &engine() noexcept { return engine_; }
private:
static std::atomic_flag flag;
static thread_local FastRandomNumberGenerator engine_;
static void OnFork() noexcept { Seed(); }
static void Seed() noexcept
{
std::random_device random_device;
std::seed_seq seed_seq{random_device(), random_device(), random_device(), random_device()};
engine_.seed(seed_seq);
}
};
std::atomic_flag TlsRandomNumberGenerator::flag;
thread_local FastRandomNumberGenerator TlsRandomNumberGenerator::engine_{};
} // namespace
FastRandomNumberGenerator &Random::GetRandomNumberGenerator() noexcept
{
static thread_local TlsRandomNumberGenerator random_number_generator{};
return TlsRandomNumberGenerator::engine();
}
uint64_t Random::GenerateRandom64() noexcept
{
return GetRandomNumberGenerator()();
}
void Random::GenerateRandomBuffer(opentelemetry::nostd::span<uint8_t> buffer) noexcept
{
auto buf_size = buffer.size();
for (size_t i = 0; i < buf_size; i += sizeof(uint64_t))
{
uint64_t value = GenerateRandom64();
if (i + sizeof(uint64_t) <= buf_size)
{
memcpy(&buffer[i], &value, sizeof(uint64_t));
}
else
{
memcpy(&buffer[i], &value, buf_size - i);
}
}
}
} // namespace common
} // namespace sdk
OPENTELEMETRY_END_NAMESPACE
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