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Delve into clock rabbit hole

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The worst issue I had with consts.sh for clock_gettime is how it defined
too many clocks. So I looked into these clocks all day to figure out how
how they overlap in functionality. I discovered counter-intuitive things
such as how CLOCK_MONOTONIC should be CLOCK_UPTIME on MacOS and BSD, and
that CLOCK_BOOTTIME should be CLOCK_MONOTONIC on MacOS / BSD. Windows 10
also has some incredible new APIs, that let us simplify clock_gettime().

  - Linux CLOCK_REALTIME         -> GetSystemTimePreciseAsFileTime()
  - Linux CLOCK_MONOTONIC        -> QueryUnbiasedInterruptTimePrecise()
  - Linux CLOCK_MONOTONIC_RAW    -> QueryUnbiasedInterruptTimePrecise()
  - Linux CLOCK_REALTIME_COARSE  -> GetSystemTimeAsFileTime()
  - Linux CLOCK_MONOTONIC_COARSE -> QueryUnbiasedInterruptTime()
  - Linux CLOCK_BOOTTIME         -> QueryInterruptTimePrecise()

Documentation on the clock crew has been added to clock_gettime() in the
docstring and in redbean's documentation too. You can read that to learn
interesting facts about eight essential clocks that survived this purge.
This is original research you will not find on Google, OpenAI, or Claude

I've tested this change by porting *NSYNC to become fully clock agnostic
since it has extensive tests for spotting irregularities in time. I have
also included these tests in the default build so they no longer need to
be run manually. Both CLOCK_REALTIME and CLOCK_MONOTONIC are good across
the entire amd64 and arm64 test fleets.
This commit is contained in:
Justine Tunney 2024-09-04 00:38:44 -07:00
parent 8f8145105c
commit dd8544c3bd
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GPG key ID: BE714B4575D6E328
87 changed files with 939 additions and 900 deletions
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41
libc/calls/clock_getres.c
View file

@ -20,24 +20,37 @@
#include "libc/dce.h"
#include "libc/intrin/describeflags.h"
#include "libc/intrin/strace.h"
#include "libc/runtime/clktck.h"
#include "libc/sysv/consts/clock.h"
#include "libc/sysv/errfuns.h"
#include "libc/time.h"
static int sys_clock_getres_poly(int clock, struct timespec *ts, int64_t real,
int64_t real_coarse, int64_t boot) {
ts->tv_sec = 0;
if (clock == CLOCK_REALTIME) {
ts->tv_nsec = real;
static uint64_t hz_to_nanos(uint64_t frequency) {
if (!frequency)
return 0;
} else if (clock == CLOCK_REALTIME_COARSE) {
ts->tv_nsec = real_coarse;
uint64_t quotient = 1000000000 / frequency;
uint64_t remainder = 1000000000 % frequency;
if (remainder > 0)
quotient += 1;
return quotient;
}
static int sys_clock_getres_poly(int clock, struct timespec *ts, int64_t prec) {
if (ts)
ts->tv_sec = 0;
if (clock == CLOCK_REALTIME || //
clock == CLOCK_BOOTTIME || //
clock == CLOCK_MONOTONIC || //
clock == CLOCK_MONOTONIC_RAW) {
if (ts)
ts->tv_nsec = prec;
return 0;
} else if (clock == CLOCK_MONOTONIC) {
ts->tv_nsec = 10;
return 0;
} else if (clock == CLOCK_BOOTTIME) {
ts->tv_nsec = boot;
} else if (clock == CLOCK_REALTIME_COARSE ||
clock == CLOCK_MONOTONIC_COARSE ||
clock == CLOCK_THREAD_CPUTIME_ID ||
clock == CLOCK_PROCESS_CPUTIME_ID) {
if (ts)
*ts = timespec_fromnanos(hz_to_nanos(CLK_TCK));
return 0;
} else {
return einval();
@ -45,11 +58,11 @@ static int sys_clock_getres_poly(int clock, struct timespec *ts, int64_t real,
}
static int sys_clock_getres_nt(int clock, struct timespec *ts) {
return sys_clock_getres_poly(clock, ts, 100, 1000000, 1000000);
return sys_clock_getres_poly(clock, ts, 100);
}
static int sys_clock_getres_xnu(int clock, struct timespec *ts) {
return sys_clock_getres_poly(clock, ts, 1000, 1000, 1000);
return sys_clock_getres_poly(clock, ts, 1000);
}
/**