[Lazarus] How to program with time in milliseconds?

[Henry Vermaak]

On Thu, May 15, 2014 at 11:41:32AM +0200, Michael Schnell wrote:
> On 05/15/2014 11:18 AM, Michael Van Canneyt wrote:
> >
> >
> >fpGetTimeOfDay is used to implement Now(). This should not be changed.
> 
> Why not, If there are better ways ?

"Better" needs to be defined here.  If you mean "faster", then you need
to call through the vDSO, so just link to the C library and use their
implementation.  Chances are that you are linking to the C library
anyway (we're on the lazarus list after all).  There isn't much reason
for fpc to implement this, but perhaps it warrants a comment in the
documentation (e.g. "glibc may have a much faster implementation that
doesn't use a syscall, if you're worried about performance").

gettimeofday() is the correct way to get the real wall clock time, there
is no "better" way for fpc to implement it (except for using
clock_gettime() with CLOCK_REALTIME, since technically gettimeofday() is
obsolete).

gettimeofday() is not what you want to use for a timer, though, since it
will change when someone sets the time on the system.  In that case you
want to use clock_gettime() with CLOCK_MONOTONIC, or even
CLOCK_MONOTONIC_RAW (linux only).  GetTickCount64 will use this on
linux, but it reduces the precision to milliseconds.

You seem a bit confused about some of these things, and people are
talking at cross purposes, so I'll end my part in the discussion
here.

Henry