Re: [Boost-users] posix_time io slow

Subject: Re: [Boost-users] posix_time io slow
From: Jeff Garland (azswdude_at_[hidden])
Date: 2010-06-22 11:28:34

Hite, Christopher wrote:
> I'm in the process of writing a logging library and I noticed that each 
> call to print out ptime took about ~50us.  Even just printing out the 
> duration time_of_day cost ~20us.
> 
> I'm using boost1.43 with g++ (GCC) 4.4.3
> g++  -ftemplate-depth-128 -O3 -finline-functions -Wno-inline -Wall 
> -pthread  -DNDEBUG
> 
> I was able to do the same thing for <1us not using stream ops (see code 
> below).
> 
> Does anyone care to optimize this stuff?  I'm considering specializing 
> my own boost::date_time::ostream_time_duration_formatter to override to 
> slow impl.

You should do this for your application -- everyone that asks me about high 
performance i/o with date time, I suggest they write their own functions 
because 1) it can typically be less general that what the library provides and 
2) it's a minimal investment in time.  Note that the first call to operator<< 
is going to incur a particularly high cost due to construction of facets under 
the hood.

> 
> template<typename int_t>
> void printDecimal(int_t d,int places,char* out){
>         int_t rest=d;
>         for(int i=0;i<places;i++){
>                 out[places-i-1]= '0'+(rest%10);
>                 rest/=10;
>         }
> }
> 
> void printDuration(const boost::posix_time::time_duration& d,char* out){
>         int64_t ticks=d.ticks();
>         int64_t us=ticks%1000000;
>         int64_t r1=ticks/1000000;
>         int64_t  s=r1%60;
>         int64_t r2=r1/60;
>         int64_t  m=r2%60;
>         int64_t  h=r2/60;
>         printDecimal(h,2,out);
>         out[2]=':';
>         printDecimal(m,2,out+3);
>         out[5]=':';
>         printDecimal(s,2,out+6);
>         out[8]='.';
>         printDecimal(us,6,out+9);
> }
> 
> ..
> 
>                 char buf[32];
>                 printDuration(pt.time_of_day(),buf);
>                 std::cout<<  buf <<" -\n"; 
>                 // <1us
> 
>                 //std::cout<<  pt.time_of_day() <<" -\n"; // ~15us
> 

A perfect demonstration of my point -- this works great for a narrow stream 
with standard delimiters in a conventional duration format -- not so well for 
a wide stream with an arbitrary format string -- for example:

BTW, I wouldn't be opposed to including a set of high performance functions in 
the library for those with this sort of application -- the real problem is 
getting folks to agree on a format to do this for (variations on iso format 
come to mind, though).  Overall though, I really don't have the time or 
inclination to produce these at the moment.

Jeff