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Ensure RNG seeded at fork #45

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Merged
willgittoes-dd merged 2 commits into from
Sep 6, 2018
Merged

Ensure RNG seeded at fork #45

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a400167
Ensure RNG seeded at fork
willgittoes-dd Sep 6, 2018
de4aa6a
Merge branch 'master' into willgittoes-dd/fork-safe-random-numbers
willgittoes-dd Sep 6, 2018
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27 changes: 25 additions & 2 deletions src/tracer.cpp
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Original file line number Diff line number Diff line change
@@ -1,5 +1,7 @@
#include <datadog/opentracing.h>
#include <pthread.h>
#include <cstdlib>
#include <random>

#include "noopspan.h"
#include "span.h"
Expand All @@ -10,10 +12,31 @@ namespace ot = opentracing;
namespace datadog {
namespace opentracing {

// Wrapper for a seeded random number generator that works with forking.
//
// See https://stackoverflow.com/q/51882689/4447365 and
// https://github.com/opentracing-contrib/nginx-opentracing/issues/52
namespace {
class TlsRandomNumberGenerator {
public:
TlsRandomNumberGenerator() { pthread_atfork(nullptr, nullptr, onFork); }

static std::mt19937_64 &generator() { return random_number_generator_; }

private:
static thread_local std::mt19937_64 random_number_generator_;

static void onFork() { random_number_generator_.seed(std::random_device{}()); }
};
} // namespace

thread_local std::mt19937_64 TlsRandomNumberGenerator::random_number_generator_{
std::random_device{}()};

uint64_t getId() {
static thread_local std::mt19937_64 source{std::random_device{}()};
static TlsRandomNumberGenerator rng;
static thread_local std::uniform_int_distribution<uint64_t> distribution;
return distribution(source);
return distribution(TlsRandomNumberGenerator::generator());
}

Tracer::Tracer(TracerOptions options, std::shared_ptr<SpanBuffer> buffer, TimeProvider get_time,
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