Ticket #7422: test.cc

#include <boost/thread/condition_variable.hpp>
#include <boost/thread/mutex.hpp>

#include <condition_variable>
#include <future>
#include <limits>
#include <cstdio>
#include <thread>
#include <mutex>

////////////////////////////////////////////////////////////////////////////////////////////////

namespace {

////////////////////////////////////////////////////////////////////////////////////////////////

class Stopwatch
{
public:
    typedef long long nsec_t;

    static nsec_t now() {
        timespec ts;
        if(clock_gettime(CLOCK_MONOTONIC, &ts))
            abort();
        return ts.tv_sec * nsec_t(1000000000) + ts.tv_nsec;
    }

    Stopwatch()
        : start_(now())
    {}

    nsec_t elapsed() const {
        return now() - start_;
    }

private:
    nsec_t start_;
};

////////////////////////////////////////////////////////////////////////////////////////////////

struct BoostTypes
{
    typedef boost::condition_variable condition_variable;
    typedef boost::mutex mutex;
    typedef boost::mutex::scoped_lock scoped_lock;
};

struct StdTypes
{
    typedef std::condition_variable condition_variable;
    typedef std::mutex mutex;
    typedef std::unique_lock<std::mutex> scoped_lock;
};

template<class Types>
struct SharedData : Types
{
    unsigned const iterations;
    unsigned counter;
    unsigned semaphore;
    typename Types::condition_variable cnd;
    typename Types::mutex mtx;
    Stopwatch::nsec_t producer_time;

    SharedData(unsigned iterations, unsigned consumers)
        : iterations(iterations)
        , counter()
        , semaphore(consumers) // Initialize to the number of consumers. (*)
        , producer_time()
    {}
};

////////////////////////////////////////////////////////////////////////////////////////////////

template<class S>
void producer_thread(S* shared_data) {
    Stopwatch sw;

    unsigned const consumers = shared_data->semaphore; // (*)
    for(unsigned i = shared_data->iterations; i--;) {
        {
            typename S::scoped_lock lock(shared_data->mtx);
            // Wait till all consumers signal.
            while(consumers != shared_data->semaphore)
                shared_data->cnd.wait(lock);
            shared_data->semaphore = 0;
            // Signal consumers.
            ++shared_data->counter;
        }
        shared_data->cnd.notify_all();
    }

    shared_data->producer_time = sw.elapsed();
}

template<class S>
void consumer_thread(S* shared_data) {
    unsigned counter = 0;
    while(counter != shared_data->iterations) {
        {
            typename S::scoped_lock lock(shared_data->mtx);
            // Wait till the producer signals.
            while(counter == shared_data->counter)
                shared_data->cnd.wait(lock);
            counter = shared_data->counter;
            // Signal the producer.
            ++shared_data->semaphore;
        }
        shared_data->cnd.notify_all();
    }
}

////////////////////////////////////////////////////////////////////////////////////////////////

template<class Types>
Stopwatch::nsec_t benchmark_ping_pong(unsigned consumer_count) {
    typedef SharedData<Types> S;

    auto best_producer_time = std::numeric_limits<Stopwatch::nsec_t>::max();

    std::vector<std::thread> consumers{consumer_count};

    // Run the benchmark 3 times and report the best time.
    for(int times = 3; times--;) {
        S shared_data{100000, consumer_count};

        // Start the consumers.
        for(unsigned i = 0; i < consumer_count; ++i)
            consumers[i] = std::thread{consumer_thread<S>, &shared_data};
        // Start the producer and wait till it finishes.
        std::thread{producer_thread<S>, &shared_data}.join();
        // Wait till consumers finish.
        for(unsigned i = 0; i < consumer_count; ++i)
            consumers[i].join();

        best_producer_time = std::min(best_producer_time, shared_data.producer_time);
    }

    return best_producer_time;
}

////////////////////////////////////////////////////////////////////////////////////////////////

} // namespace

////////////////////////////////////////////////////////////////////////////////////////////////

// sudo chrt -f 99 /usr/bin/time -f "\n***\ntime: %E\ncontext switches: %c\nwaits: %w" /home/max/otsquant/build/Linux-x86_64-64.g++-release/test/test

/*

Producer-consumer ping-pong tests. It aims to benchmark condition variables with and without
thread cancellation support by comparing the time it took to complete the benchmark.

Condition variable with thread cancellation support is boost::condition_variable from
boost-1.51. Without - std::condition_variable that comes with gcc-4.7.2.

One producer, one to CONSUMER_MAX consumers. The benchmark calls
condition_variable::notify_all() without holding a mutex to maximize contention within this
function. Each benchmark for a number of consumers is run three times and the best time is
picked to get rid of outliers.

The results are reported for each benchmark for a number of consumers. The most important number
is (std - boost) / std * 100. Positive numbers are when boost::condition_variable is faster,
negative it is slower.

 */

int main() {
    enum { CONSUMER_MAX = 20 };

    struct {
        Stopwatch::nsec_t boost, std;
    } best_times[CONSUMER_MAX] = {};

    for(unsigned i = 1; i <= CONSUMER_MAX; ++i) {
        auto& b = best_times[i - 1];
        b.std = benchmark_ping_pong<StdTypes>(i);
        b.boost = benchmark_ping_pong<BoostTypes>(i);

        std::printf("consumers:                 %4d\n", i);
        std::printf("best std producer time:   %15.9fsec\n", b.std * 1e-9);
        std::printf("best boost producer time: %15.9fsec\n", b.boost * 1e-9);
        std::printf("(std - boost) / std:       %7.2f%%\n", (b.std - b.boost) * 100. / b.std);
    }

    printf("\ncsv:\n\n");
    printf("consumers,(std-boost)/std,std,boost\n");
    for(unsigned i = 1; i <= CONSUMER_MAX; ++i) {
        auto& b = best_times[i - 1];
        printf("%d,%f,%lld,%lld\n", i, (b.std - b.boost) * 100. /  b.std, b.std, b.boost);
    }
}