Re: [Boost-users] [Signals] Another performance discussion

23 Jul 2009


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On Thursday 23 July 2009, Sajjan Kalle wrote:
...
2009/7/23 Sajjan Kalle :
...
Profiling the project in question where the performance of
boost::signals is one of the problems it seems two of the bottlenecks
is slot_call_iterator::increment and slot_call_iterator::equal, and in
those in particular find_if, which seems to be used for incrementing
the iterator. I'll try to create a sample with timing on a bit more
fragmented world like use case.
I'll throw signals2 in to the mix once I've built 1.39, in the
meantime, here's a new variant which depends on only stl and boost.
#include <iostream>
#include "boost/signals.hpp"
#include <vector>
#include "boost/function.hpp"
#include "boost/timer.hpp"
#include <cstdlib>
#include <algorithm>
void foo( )
{
}
int main()
{
  std::vector< boost::function< void ( void ) > > manualSignal;
  boost::signal< void ( void ) > boostSignalFragmented,
boostSignalUnfragmented; typedef std::vector< boost::signals::connection >
ConnectionVector; ConnectionVector connections;
  for( unsigned int i = 0; i < 10000; ++i )
  {
      manualSignal.push_back( &foo );
      boostSignalUnfragmented.connect( &foo );
  }
  for( unsigned int i = 0; i < 100000; ++i )
  {
      connections.push_back( boostSignalFragmented.connect( &foo ) );
  }
  for( unsigned int i = 0; i < 90000; ++i )
  {
      ConnectionVector::iterator index = connections.begin() + rand() %
connections.size();
      (*index).disconnect();
      *index = *connections.rbegin();
      connections.erase( connections.begin() + connections.size() - 1 );
  }
  {
      boost::timer tm;
      for( unsigned int i = 0; i < 1000; ++i )
      {
      	for( unsigned int j = 0; j < 10000; ++j )
      		manualSignal[ i ]( );
      }
      double elapsed = tm.elapsed();
      std::cout << "vector variant: " << elapsed << std::endl;
  }
  {
      boost::timer tm;
      for( unsigned int i = 0; i < 1000; ++i )
      {
      	boostSignalUnfragmented( );
      }
      double elapsed = tm.elapsed();
      std::cout << "boost::signal Unfragmented variant: " << elapsed <<
std::endl; }
  {
      boost::timer tm;
      for( unsigned int i = 0; i < 1000; ++i )
      {
      	boostSignalFragmented( );
      }
      double elapsed = tm.elapsed();
      std::cout << "boost::signal Fragmented variant: " << elapsed <<
std::endl; }
}
This gives me ~0.032 on vector, ~1.80 on unfragmented boost::signal
and lastly ~3.04 on fragmented boost::signal.
On what kind of hardware?  On a 3.2GHz Pentium D running Linux with gcc 
4.3.2 , I get:

$ g++ -Wall -O2 -I /usr/local/boost-1_39_0/include/boost-1_39/ 
sigbench.cpp -lboost_signals-gcc43-mt
$ ./a.out
vector variant: 0.12
boost::signal Unfragmented variant: 0.89
boost::signal Fragmented variant: 2
$ ./a.out
vector variant: 0.12
boost::signal Unfragmented variant: 0.52
boost::signal Fragmented variant: 2.07

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Re: [Boost-users] [Signals] Another performance discussion

Frank Mori Hess