id	summary	reporter	owner	description	type	status	milestone	component	version	severity	resolution	keywords	cc
4002	UUID documentation improvement	harris.pc@…	Andy Tompkins	"I get ""uninitialised value(s)"" warnings in valgrind when I use the following code:

boost::uuids::random_generator gen;
boost::uuids::uuid u = gen();
if (u == u) // for valgrind's benefit
  whatever();

In the example, when I do not supply a random number generator to 'gen', it calls:
        detail::seed(*pURNG);

Which does not initialise all its state variables (like rd_[]) before generating random numbers.

I assume this is done to try and generate decent random numbers from uninitialised memory, especially when there is no /dev/urandom or similar available.  That is ok, I suppose.

However, it makes valgrind very noisy when comparing uuids and thus generates a lot of false-positives to sift through.

It would be great if the documentation could talk a bit about this, and also suggest that you use a pattern like the following if the library-user wants to silence valgrind reports:

boost::mt19937 ran;
uuids::random_generator gen(ran);

It would be nice if it could also tell the library user why this might not be such a good idea. (eg mt19937 doesn't seed the random values as randomly as uuid's seed_rnd.hpp, right?).

Or perhaps you can surround the detail::seed() call with #ifdefs to allow the user to control when uninitialised memory is used for seeding (helpful to turn off when debugging).

Thanks,
Paul
"	Bugs	closed	Boost 1.43.0	uuid	Boost 1.42.0	Optimization	fixed