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Re: Why is java consumer/producer so much faster than C++

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On 24/07/2012 21:45, Melzzzzz wrote:
> This is version with array (identical implementation
> as ArrayBlockingQueue in Java), instead of deque (I
> used atomic type for count_). This executes about same speed as Java
> as atomic type slows it down a bit.

> Sadly, no noticing difference between deque and array.

Right, it may well depend on how smart the std::deque::allocator_type is.

Below is a version of the BlockingQueue using spin locks. Compared to 
the original version in Java it is about 2.5 times faster on my 
platform, provided that you remove std::rand() from the test, as it 
seems to be a real bottleneck and does not give any precious 
informations about the efficiency of the Queue (which is the thing to 
measure after all).

Let me know your results.

---

#include <thread>
#include <cstdlib>
#include <functional>
#include <atomic>
#include <memory>
#include <type_traits>

class spinlock_mutex {
     std::atomic_flag flag = ATOMIC_FLAG_INIT;
public:

     void lock() {
         while (flag.test_and_set(std::memory_order_acquire)) {
             std::this_thread::yield();
         };
     }

     void unlock() {
         flag.clear(std::memory_order_release);
     }
};

template <class T, class A = std::allocator<T >>
class BlockingQueue {
     const std::size_t cap_;
     A alloc_;
     T* queue_;
     std::size_t n = 0, b = 0, f = 0;
     spinlock_mutex m_;
public:

     BlockingQueue(const std::size_t cap, const A& alloc = A())
     : cap_(cap), alloc_(alloc), queue_(alloc_.allocate(cap)) { }

     ~BlockingQueue() {
         alloc_.deallocate(queue_, cap_);
     }

     static_assert(std::is_nothrow_move_constructible<T>::value, 
"BlockingQueue cannot be exception-safe");

     void put(const T t) {
         for (;;) {
             m_.lock();
             if (n < cap_)
                 break;
             m_.unlock();
         }
         alloc_.construct(&queue_[f], std::move(t));
         f = ++f % cap_;
         ++n;
         m_.unlock();
     }

     T take() {
         for (;;) {
             m_.lock();
             if (n > 0)
                 break;
             m_.unlock();
         }
         const T t = std::move(queue_[b]);
         alloc_.destroy(&queue_[b]);
         b = ++b % cap_;
         --n;
         m_.unlock();
         return t;
     }
};

int main() {
     BlockingQueue<int> produced(100000);
     const int nitems = 100000000;
     std::srand(12345);


     std::function<void() > f_prod = [&](){
         int i = nitems;
         while (i-- > 0) {
             produced.put(i);
         }
     };

     std::thread producer1(f_prod);

     std::function<void() > f_cons = [&](){
         const int size = 10000;
         int arr[size];
         int i = nitems;
         while (i-- > 0) {
             arr[std::rand() % size] = produced.take();
         }
     };

     std::thread consumer1(f_cons);

     producer1.join();
     consumer1.join();
}

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Why is java consumer/producer so much faster than C++ Melzzzzz <mel@zzzzz.com> - 2012-07-22 23:59 +0200
  Re: Why is java consumer/producer so much faster than C++ Joshua Maurice <joshuamaurice@gmail.com> - 2012-07-22 15:42 -0700
    Re: Why is java consumer/producer so much faster than C++ Melzzzzz <mel@zzzzz.com> - 2012-07-23 01:28 +0200
      Re: Why is java consumer/producer so much faster than C++ Luca Risolia <luca.risolia@studio.unibo.it> - 2012-07-23 02:03 +0200
        Re: Why is java consumer/producer so much faster than C++ Melzzzzz <mel@zzzzz.com> - 2012-07-23 12:17 +0200
          Re: Why is java consumer/producer so much faster than C++ Luca Risolia <luca.risolia@studio.unibo.it> - 2012-07-24 00:33 +0200
            Re: Why is java consumer/producer so much faster than C++ Bo Persson <bop@gmb.dk> - 2012-07-24 19:50 +0200
  Re: Why is java consumer/producer so much faster than C++ Juha Nieminen <nospam@thanks.invalid> - 2012-07-23 06:37 +0000
    Re: Why is java consumer/producer so much faster than C++ Melzzzzz <mel@zzzzz.com> - 2012-07-23 12:33 +0200
      Re: Why is java consumer/producer so much faster than C++ Juha Nieminen <nospam@thanks.invalid> - 2012-07-23 11:46 +0000
        Re: Why is java consumer/producer so much faster than C++ Melzzzzz <mel@zzzzz.com> - 2012-07-23 15:33 +0200
  Re: Why is java consumer/producer so much faster than C++ Zoltan Juhasz <zoltan.juhasz@gmail.com> - 2012-07-23 06:57 -0700
    Re: Why is java consumer/producer so much faster than C++ Melzzzzz <mel@zzzzz.com> - 2012-07-23 18:42 +0200
      Re: Why is java consumer/producer so much faster than C++ Howard Hinnant <howard.hinnant@gmail.com> - 2012-07-23 13:23 -0700
        Re: Why is java consumer/producer so much faster than C++ Melzzzzz <mel@zzzzz.com> - 2012-07-24 00:32 +0200
          Re: Why is java consumer/producer so much faster than C++ Howard Hinnant <howard.hinnant@gmail.com> - 2012-07-23 18:11 -0700
            Re: Why is java consumer/producer so much faster than C++ Melzzzzz <mel@zzzzz.com> - 2012-07-24 11:21 +0200
            Re: Why is java consumer/producer so much faster than C++ Melzzzzz <mel@zzzzz.com> - 2012-07-24 21:45 +0200
              Re: Why is java consumer/producer so much faster than C++ Luca Risolia <luca.risolia@studio.unibo.it> - 2012-07-24 23:24 +0200
                Re: Why is java consumer/producer so much faster than C++ Melzzzzz <mel@zzzzz.com> - 2012-07-25 00:48 +0200
                Re: Why is java consumer/producer so much faster than C++ Luca Risolia <luca.risolia@studio.unibo.it> - 2012-07-25 01:21 +0200
              Re: Why is java consumer/producer so much faster than C++ Howard Hinnant <howard.hinnant@gmail.com> - 2012-07-24 17:35 -0700
              Re: Why is java consumer/producer so much faster than C++ Luca Risolia <luca.risolia@studio.unibo.it> - 2012-07-26 21:19 +0200
                Re: Why is java consumer/producer so much faster than C++ Melzzzzz <mel@zzzzz.com> - 2012-07-26 21:56 +0200
                Re: Why is java consumer/producer so much faster than C++ Luca Risolia <luca.risolia@studio.unibo.it> - 2012-07-26 22:15 +0200
                Re: Why is java consumer/producer so much faster than C++ Melzzzzz <mel@zzzzz.com> - 2012-07-26 23:01 +0200
                Re: Why is java consumer/producer so much faster than C++ Luca Risolia <luca.risolia@studio.unibo.it> - 2012-07-26 23:12 +0200
                Re: Why is java consumer/producer so much faster than C++ Melzzzzz <mel@zzzzz.com> - 2012-07-27 00:24 +0200
                Re: Why is java consumer/producer so much faster than C++ Melzzzzz <mel@zzzzz.com> - 2012-07-27 00:48 +0200
                Re: Why is java consumer/producer so much faster than C++ Melzzzzz <mel@zzzzz.com> - 2012-07-27 05:43 +0200
                Re: Why is java consumer/producer so much faster than C++ Melzzzzz <mel@zzzzz.com> - 2012-07-27 07:43 +0200
                Re: Why is java consumer/producer so much faster than C++ Marc <marc.glisse@gmail.com> - 2012-07-26 21:10 +0000
                Re: Why is java consumer/producer so much faster than C++ Donkey Hottie <donkey@fredriksson.dy.fi> - 2012-07-27 01:05 +0300
                Re: Why is java consumer/producer so much faster than C++ Paavo Helde <myfirstname@osa.pri.ee> - 2012-07-26 17:12 -0500
        Re: Why is java consumer/producer so much faster than C++ yatremblay@bel1lin202.(none) (Yannick Tremblay) - 2012-07-24 12:51 +0000
          Re: Why is java consumer/producer so much faster than C++ Melzzzzz <mel@zzzzz.com> - 2012-07-24 17:47 +0200
            Re: Why is java consumer/producer so much faster than C++ yatremblay@bel1lin202.(none) (Yannick Tremblay) - 2012-07-25 08:09 +0000
              Re: Why is java consumer/producer so much faster than C++ Howard Hinnant <howard.hinnant@gmail.com> - 2012-07-25 08:46 -0700
  Re: Why is java consumer/producer so much faster than C++ Dombo <dombo@disposable.invalid> - 2012-07-23 22:57 +0200
    Re: Why is java consumer/producer so much faster than C++ Joshua Maurice <joshuamaurice@gmail.com> - 2012-07-23 21:54 -0700
      Re: Why is java consumer/producer so much faster than C++ Jorgen Grahn <grahn+nntp@snipabacken.se> - 2012-07-24 12:50 +0000
  Re: Why is java consumer/producer so much faster than C++ James Kanze <james.kanze@gmail.com> - 2012-07-29 03:27 -0700
    Re: Why is java consumer/producer so much faster than C++ Melzzzzz <mel@zzzzz.com> - 2012-07-29 14:40 +0200
  Re: Why is java consumer/producer so much faster than C++ Ricardo Nabinger Sanchez <rnsanchez@wait4.org> - 2012-08-14 22:48 +0000

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