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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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38
libc/sysv/consts/clock.h
View file

@ -2,42 +2,26 @@
#define COSMOPOLITAN_LIBC_SYSV_CONSTS_CLOCK_H_
COSMOPOLITAN_C_START_
extern const int CLOCK_BOOTTIME;
extern const int CLOCK_BOOTTIME_ALARM;
extern int CLOCK_REALTIME_COARSE;
extern const int CLOCK_MONOTONIC;
extern const int CLOCK_MONOTONIC_COARSE;
extern const int CLOCK_MONOTONIC_FAST;
extern const int CLOCK_MONOTONIC_PRECISE;
extern int CLOCK_MONOTONIC_RAW;
extern int CLOCK_MONOTONIC_RAW_APPROX;
extern const int CLOCK_PROCESS_CPUTIME_ID;
extern const int CLOCK_PROF;
extern const int CLOCK_REALTIME_ALARM;
extern const int CLOCK_REALTIME_COARSE;
extern const int CLOCK_REALTIME_FAST;
extern const int CLOCK_REALTIME_PRECISE;
extern const int CLOCK_SECOND;
extern const int CLOCK_TAI;
extern int CLOCK_MONOTONIC_COARSE;
extern const int CLOCK_THREAD_CPUTIME_ID;
extern const int CLOCK_UPTIME;
extern const int CLOCK_UPTIME_FAST;
extern const int CLOCK_UPTIME_PRECISE;
extern const int CLOCK_PROCESS_CPUTIME_ID;
extern const int CLOCK_BOOTTIME;
COSMOPOLITAN_C_END_
#define CLOCK_REALTIME 0
#define CLOCK_REALTIME_FAST CLOCK_REALTIME_FAST
#define CLOCK_REALTIME_PRECISE CLOCK_REALTIME_PRECISE
#define CLOCK_REALTIME_COARSE CLOCK_REALTIME_COARSE
#define CLOCK_REALTIME 0
#define CLOCK_REALTIME_COARSE CLOCK_REALTIME_COARSE
#define CLOCK_MONOTONIC CLOCK_MONOTONIC
#define CLOCK_MONOTONIC_RAW CLOCK_MONOTONIC_RAW
#define CLOCK_MONOTONIC_RAW_APPROX CLOCK_MONOTONIC_RAW_APPROX
#define CLOCK_MONOTONIC_FAST CLOCK_MONOTONIC_FAST
#define CLOCK_MONOTONIC_PRECISE CLOCK_MONOTONIC_PRECISE
#define CLOCK_MONOTONIC_COARSE CLOCK_MONOTONIC_COARSE
#define CLOCK_MONOTONIC CLOCK_MONOTONIC
#define CLOCK_MONOTONIC_RAW CLOCK_MONOTONIC_RAW
#define CLOCK_MONOTONIC_COARSE CLOCK_MONOTONIC_COARSE
#define CLOCK_THREAD_CPUTIME_ID CLOCK_THREAD_CPUTIME_ID
#define CLOCK_PROCESS_CPUTIME_ID CLOCK_PROCESS_CPUTIME_ID
#define CLOCK_BOOTTIME CLOCK_BOOTTIME
#endif /* COSMOPOLITAN_LIBC_SYSV_CONSTS_CLOCK_H_ */