[boost] Serious problem with boost::thread & timed_wait

From: Markus Schöpflin (markus.schoepflin_at_[hidden])
Date: 2002-05-10 08:24:33

Hi all,

the wait functions in boost::thread internally use a function
to_duration() which fails to give correct results under certain
circumstances (overflow of nsec to sec) with at least MSVC6SP5.

In my case this resulted in spurious 5 seconds waits instead of
50 milliseconds when using boost::condition::timed_wait().

The root of the problem is that you get quite some interesting
results when doing signed integer division on this compiler.
Try it with the following little program. :-)

--%<--
#include <iostream>
int main()
{
  unsigned long a = 2;
  signed long b = -2 / a;
  std::cout << b;
  return 0;
}
-->%--

As to_duration uses to following expression to calculate the
difference in milliseconds it is affected by this compiler bug
as well.

milliseconds = static_cast<unsigned>(
  ((xt.sec - cur.sec) * MILLISECONDS_PER_SECOND) +
    (((xt.nsec - cur.nsec) + (NANOSECONDS_PER_MILLISECOND/2)) /
-------^^^^^^^^^^^^^^^^^^ (sometimes negative)
    NANOSECONDS_PER_MILLISECOND));

The fix is easy enough. Change all the constants at the top of
"timeconv.inl" to macros and the compiler generates the right
code.

Markus