CLOCK_MONOTONIC_RAW is linux-specific (macOS later supported it but it
has its own timer code) and not neccessarily available everywhere like
on BSDs. It makes sense to prefer it because mpv does a lot of
measurements at small intervals (e.g. every frame) so theoretically it
should be more accurate. However if the OS doesn't have it, fallback to
CLOCK_MONOTONIC instead which is almost exactly the same and very widely
supported across unix-like systems. This clock is technically optional
according to POSIX, but any half-decent OS supports it anyway (sorry
Solaris users). As a benefit, we now know that the clock from mp_time is
always monotonic.
Linux and macOS already use nanosecond resolution for their sleep
functions. It was just being converted from microseconds before. Since
we have mp_time_ns now, go ahead and bump the precision here. The timer
for windows uses some timeBeginPeriod thing which I'm not sure what it
does really but whatever just convert the units to ms like they were
doing before. There's really no reason to keep the mp_sleep_us helper
around. A multiplication by 1000 is trivial and underlying OS clocks
have nanosecond precision.
All authors have agreed, with the following exceptions:
e68d7f6858: wight wasn't asked (I think...), but even if he modified the
patch he applied, all code added by it was removed again later.
cb7768f9bb: nick could not be reached, but the declarations he added as
well as the full timer.c file were deleted again in cff81fe498 and
f800a42e45 (did it really take 6 years to remove unused declarations?).
ffaf4af230: it looks like this person wasn't contacted, but the code
added was removed again in f544bcf105.
Apparently, this is always _really_ monotonic, despite what the Linux
manpages say. So this should be much better than gettimeofday(). (At
times there were kernel bugs which broke the monotonic property.)
From the perspective of the player, time can still be discontinuous
(you could just stop the process with ^Z), but at least it's guaranteed
to be monotonic without further hacks required.
Also note that clock_gettime() returns the time in nanoseconds. We want
microseconds only, because that's the unit we chose internally. Another
problem is that nanoseconds can wrap pretty quickly (less than 300 years
in 63 bits), so it's just better to use microseconds. The devision won't
make the code that much slower (compilers can avoid a real division).
Note: this expects that the system provides clock_gettime() as well as
CLOCK_MONOTONIC. Both are optional according to POSIX. The only system
I know which doesn't have these, OSX, has seperate timer code anyway,
but I still don't know whether more obscure (yet supported) platforms
have a problem with this, so I'm playing safely. But this still expects
that CLOCK_MONOTONIC always works at runtime if it's defined.
The configure followed 5 different convetions of defines because the next guy
always wanted to introduce a new better way to uniform it[1]. For an
hypothetic feature 'hurr' you could have had:
* #define HAVE_HURR 1 / #undef HAVE_DURR
* #define HAVE_HURR / #undef HAVE_DURR
* #define CONFIG_HURR 1 / #undef CONFIG_DURR
* #define HAVE_HURR 1 / #define HAVE_DURR 0
* #define CONFIG_HURR 1 / #define CONFIG_DURR 0
All is now uniform and uses:
* #define HAVE_HURR 1
* #define HAVE_DURR 0
We like definining to 0 as opposed to `undef` bcause it can help spot typos
and is very helpful when doing big reorganizations in the code.
[1]: http://xkcd.com/927/ related
Make OS specific timer code export a mp_raw_time_us() function, and
add generic implementations of GetTimer()/GetTimerMS() using this
function. New mpv code is supposed to call mp_time_us() in situations
where precision is absolutely needed, or mp_time_s() otherwise.
Make it so that mp_time_us() will return a value near program start.
We don't set it to 0 though to avoid confusion with relative vs.
absolute time. Instead, pick an arbitrary offset.
Move the test program in timer-darwin.c to timer.c, and modify it to
work with the generic timer functions.
Move the code calculating time delta since last query out of the
platform-specific drivers and into mplayer.c. The platform-specific
drivers now return absolute values only.
The way the code in timer-darwin.c uses doubles in wrapping arithmetic
looks questionable and this change might make problems in it more
visible.
Kacper Michajłow
Dudemanguy
Thomas Weißschuh
wm4
Marcin Kurczewski
Stefano Pigozzi
Uoti Urpala
diego
Uoti Urpala