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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
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