boost accumulator rolling count non zero

I am trying to use accumulators to find out statistics for a given activity per sec. Below are the two stats I would like to compute

Number of times activity has been triggered
Sum of the total weight triggered by the activity.

To achieve I have assumed a granularity by 10 msecs and considering 100 buckets ( per sec ).
Actvity Thread inserts into accumulator whenever there is an event
Null Activity Thread wakes up every 10 msecs to insert 0 in the weight.

Psuedo code below

#include <boost/accumulators/accumulators.hpp>
#include <boost/accumulators/statistics/stats.hpp>
#include <boost/accumulators/statistics/rolling_count.hpp>
#include <boost/accumulators/statistics/rolling_sum.hpp>

using namespace boost::accumulators;

#define MAX_WEIGHT 100
#define MAX_ACIVITY 10

accumulator_set<double, features<tag::rolling_count, tag::rolling_sum> > acc(tag::rolling_window::window_size = 100);

void null_run()//invoked every 10 msecs 
{
  //mutex protected
  acc(0);
}

void activity_triggered(int weight) // triggered by an external event
{
  //mutex protected
  acc(weight);
  if (checkStatus() == false)
  {
    printf("Max quantity per sec reached stop ");
    exit()
  }
}


bool checkStatus()
{
   int weightPerSec  = rolling_sum(acc);
   //here I would like to get the count only if non zero may be rolling_count_non_zero()??
   int acitivitiesPersec = rolling_count(acc); 
   
   if (weightPerSec > MAX_WEIGHT)
     return false;
   if (acitivitiesPersec > MAX_ACTIVITY)
     return false;
   return true;
}

Using above technique i am able to achieve weight entered in the last second but how do I achieve how many times has the activity been triggered in the last sec using boost accumulators ?

Solution

Sure rolling_count_non_zero sounds like an appropriate name for what you want (although it could have been somewhat more generic, maybe rolling_count_if?).

Boost.accumulators users guide describes how to write your own accumulators, features, and extractors, simply following that description, the following seems to work:

namespace boost { namespace accumulators { namespace impl {
    template<typename Sample>
    struct rolling_count_non_zero : accumulator_base
    {
        typedef std::size_t result_type;
        rolling_count_non_zero(dont_care) : cnt_() {}
        template<typename Args>
        void operator ()(Args const &args)
        {
            if(args[sample] != 0)
                ++cnt_;
            if(is_rolling_window_plus1_full(args)
               && rolling_window_plus1(args).front() != 0 )
                --cnt_;
        }
        template<typename Args>
        result_type result(Args const &args) const { return cnt_; }
    private:
        std::size_t cnt_;
    };

} namespace tag {
    struct rolling_count_non_zero : depends_on< rolling_window_plus1 >
    {
        typedef accumulators::impl::rolling_count_non_zero< mpl::_1 > impl;
    };
} namespace extract {
    extractor<tag::rolling_count_non_zero> const rolling_count_non_zero = {};
}
using extract::rolling_count_non_zero;
}}

live demo: http://coliru.stacked-crooked.com/a/bc4bea090690f26d