Hi Alan
> The only trouble with the above fix is not every Unix platform has > /dev/urandom (although from the above URL most do). > > So I would like to change the above fix to check for /dev/urandom > and use it if it exists, but otherwise fall back to using > /dev/random. > > How do I do that in C++? This is not a C++ (or C) issue. This is ideal for cmake to check, the same way it detects for other possible system functions/features availability. I never did this before, but I think the way it works it is on the cmake script do a small C or C++ program embedded in the script that includes "/dev/urandom" in some way, for example std::fstream fin( "/dev/urandom", std::ios::in ); and then check if it compiles and pass the result to cmake > > /dev/urandom (although from the above URL most do). yes, by reading the Wikipedia page, they don't say of any system that does not have "/dev/urandom" -Pedro On 2016-12-19 16:14, Alan W. Irwin wrote: > On 2016-12-19 19:47-0000 p.d.rosenb...@gmail.com wrote: > >> Hi Alan > >> I am on my commute home right now. But if you want to test if the >> random number generator is the cause then find the Rand constructor – >> Rand::Rand() and comment out everything, replacing it with a single >> line that sets the seed (probably m_seed or something) to a fixed >> value, like 0. That will show whether generating the seed is causing >> the slowdown. > > Hi Phil: > > Thanks to your leap of insight that it was entropy and the random > number generator that was the source of the issue, I have now found > the fix! My tests show all pauses are now gone after the following > local change, but I need C++ help to finalize this fix. > > diff --git a/drivers/wxwidgets_dev.cpp b/drivers/wxwidgets_dev.cpp > index 1131e9b..e0f215f 100644 > --- a/drivers/wxwidgets_dev.cpp > +++ b/drivers/wxwidgets_dev.cpp > @@ -603,7 +603,7 @@ public: > #ifdef WIN32 > rand_s( &m_seed ); > #else > - std::fstream fin( "/dev/random", std::ios::in ); > + std::fstream fin( "/dev/urandom", std::ios::in ); > fin.read( (char *) ( &m_seed ), sizeof ( m_seed ) ); > fin.close(); > #endif > > The difference between /dev/random and /dev/urandom on Linux is the > former is blocking (and therefore only recommended if you need > highest > security and are willing to wait for it) while the latter is not > blocking and gives adequate pseudo-randomness for most purposes (such > as ours). See <https://en.wikipedia.org/wiki//dev/random> for further > details. > > The only trouble with the above fix is not every Unix platform has > /dev/urandom (although from the above URL most do). > > So I would like to change the above fix to check for /dev/urandom > and use it if it exists, but otherwise fall back to using > /dev/random. > > How do I do that in C++? > > Or, better yet show me by going ahead and making the commit to that > effect. > > Alan > __________________________ > Alan W. Irwin > > Astronomical research affiliation with Department of Physics and > Astronomy, > University of Victoria (astrowww.phys.uvic.ca). > > Programming affiliations with the FreeEOS equation-of-state > implementation for stellar interiors (freeeos.sf.net); the Time > Ephemerides project (timeephem.sf.net); PLplot scientific plotting > software package (plplot.sf.net); the libLASi project > (unifont.org/lasi); the Loads of Linux Links project (loll.sf.net); > and the Linux Brochure Project (lbproject.sf.net). > __________________________ > > Linux-powered Science > __________________________ -- Pedro Vicente pedro.vice...@space-research.org http://www.space-research.org/ ------------------------------------------------------------------------------ Developer Access Program for Intel Xeon Phi Processors Access to Intel Xeon Phi processor-based developer platforms. With one year of Intel Parallel Studio XE. Training and support from Colfax. Order your platform today.http://sdm.link/intel _______________________________________________ Plplot-devel mailing list Plplot-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/plplot-devel
