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