binary-trees C++ g++ #3 program

/* The Computer Language Benchmarks Game
 * https://salsa.debian.org/benchmarksgame-team/benchmarksgame/
 *
 * contributed by Jon Harrop
 * modified by Alex Mizrahi
 * modified by Andreas Schäfer
 * very minor omp tweak by The Anh Tran
 * Jeff Wofford: replaced omp dependency with C++11 threading and load-based job distribution.
 *  *reset*
 */

#include <iostream>
#include <stdlib.h>
#include <stdio.h>
#include <thread>
#include <mutex>
#include <vector>

#include <boost/pool/object_pool.hpp>


const size_t   LINE_SIZE = 64;


struct Node
{
   Node *l, *r;
   
   Node() : l(0), r(0)
   {}
   Node(Node *l2, Node *r2) : l(l2), r(r2)
   {}
   
   int check() const
   {
      if (l)
         return l->check() + 1 + r->check();
      else return 1;
   }
};

typedef boost::object_pool<Node> NodePool;


Node *make(int d, NodePool &store)
{
   if (d > 0)
      return store.construct(   make(d-1, store),
                        make(d-1, store)   );
   return store.construct();
}

const unsigned THREADS_TO_USE = std::max( 1U, std::min( 4U, std::thread::hardware_concurrency() ));

int main(int argc, char *argv[])
{
   const int min_depth = 4;
   const int max_depth = std::max(min_depth+2,
                      (argc == 2 ? atoi(argv[1]) : 10));
   const int stretch_depth = max_depth+1;
   
   // Alloc then dealloc stretchdepth tree
   {
      NodePool store;
      Node *c = make(stretch_depth, store);
      std::cout << "stretch tree of depth " << stretch_depth << "\t "
              << "check: " << c->check() << std::endl;
   }
   
   NodePool long_lived_store;
   Node *long_lived_tree = make(max_depth, long_lived_store);
   
   // buffer to store output of each thread
   std::unique_ptr< char > outputstr{ new char[ LINE_SIZE * (max_depth + 1)] };
   
   std::mutex mutex;
   int nextDepthToProcess = min_depth;
   
   const auto work = [&]()
   {
      while(true)
      {
         std::unique_lock< decltype(mutex) > lock(mutex);
         const int d = nextDepthToProcess;
         if(d > max_depth)
         {
            return;
         }
         nextDepthToProcess += 2;
         lock.unlock();
         
         const int iterations = 1 << (max_depth - d + min_depth);
         int checksum = 0;
         
         for(int i = 1; i <= iterations; ++i)
         {
            NodePool store;
            Node *a = make(d, store);
            checksum += a->check();
         }
         
         // each thread write to separate location
         sprintf(outputstr.get() + LINE_SIZE * d, "%d\t trees of depth %d\t check: %d\n", iterations, d, checksum);
      }
   };

   std::vector< std::thread > threads(THREADS_TO_USE - 1);
   for(auto& thread : threads)
   {
      thread = std::thread{ work };
   }

   work();
   
   for(auto& thread : threads)
   {
      thread.join();
   }
   
   // print all results
   for (int d = min_depth; d <= max_depth; d += 2)
      printf("%s", outputstr.get() + (d * LINE_SIZE) );
   
   std::cout << "long lived tree of depth " << max_depth << "\t "
           << "check: " << (long_lived_tree->check()) << "\n";
   
   return 0;
}
    

NOTES:
64-bit Ubuntu quad core
g++ (Ubuntu 9.3.0-10ubuntu2) 9.3.0


Mon, 04 May 2020 17:30:46 GMT

MAKE:
/usr/bin/g++ -c -pipe -O3 -fomit-frame-pointer -march=core2   binarytrees.gpp-3.c++ -o binarytrees.gpp-3.c++.o &&  \
        /usr/bin/g++ binarytrees.gpp-3.c++.o -o binarytrees.gpp-3.gpp_run -lpthread 
rm binarytrees.gpp-3.c++

7.06s to complete and log all make actions

COMMAND LINE:
./binarytrees.gpp-3.gpp_run 21

PROGRAM OUTPUT:
stretch tree of depth 22	 check: 8388607
2097152	 trees of depth 4	 check: 65011712
524288	 trees of depth 6	 check: 66584576
131072	 trees of depth 8	 check: 66977792
32768	 trees of depth 10	 check: 67076096
8192	 trees of depth 12	 check: 67100672
2048	 trees of depth 14	 check: 67106816
512	 trees of depth 16	 check: 67108352
128	 trees of depth 18	 check: 67108736
32	 trees of depth 20	 check: 67108832
long lived tree of depth 21	 check: 4194303