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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
No known key found for this signature in database
GPG key ID: BE714B4575D6E328
87 changed files with 939 additions and 900 deletions
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44
third_party/nsync/testing/mu_test.c vendored
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@ -19,12 +19,12 @@
#include "libc/calls/calls.h"
#include "libc/str/str.h"
#include "libc/thread/thread.h"
#include "third_party/nsync/time.h"
#include "third_party/nsync/cv.h"
#include "third_party/nsync/mu_wait.h"
#include "third_party/nsync/testing/closure.h"
#include "third_party/nsync/testing/smprintf.h"
#include "third_party/nsync/testing/testing.h"
#include "libc/sysv/consts/clock.h"
#include "third_party/nsync/testing/time_extra.h"
/* The state shared between the threads in each of the tests below. */
@ -68,7 +68,7 @@ static void test_data_wait_for_all_threads (test_data *td) {
while (td->finished_threads != td->n_threads) {
nsync_cv_wait_with_deadline_generic (&td->done, td->mu_in_use,
td->lock, td->unlock,
CLOCK_REALTIME,
NSYNC_CLOCK,
nsync_time_no_deadline, NULL);
}
(*td->unlock) (td->mu_in_use);
@ -113,7 +113,7 @@ static void void_mu_unlock (void *mu) {
static void test_mu_nthread (testing t) {
int loop_count = 100000;
nsync_time deadline;
deadline = nsync_time_add (nsync_time_now (), nsync_time_ms (1500));
deadline = nsync_time_add (nsync_time_now (NSYNC_CLOCK), nsync_time_ms (1500));
do {
int i;
test_data td;
@ -133,7 +133,7 @@ static void test_mu_nthread (testing t) {
td.n_threads*td.loop_count, td.i));
}
loop_count *= 2;
} while (nsync_time_cmp (nsync_time_now (), deadline) < 0);
} while (nsync_time_cmp (nsync_time_now (NSYNC_CLOCK), deadline) < 0);
}
/* void pthread_mutex_lock */
@ -152,7 +152,7 @@ static void void_pthread_mutex_unlock (void *mu) {
static void test_mutex_nthread (testing t) {
int loop_count = 100000;
nsync_time deadline;
deadline = nsync_time_add (nsync_time_now (), nsync_time_ms (1500));
deadline = nsync_time_add (nsync_time_now (NSYNC_CLOCK), nsync_time_ms (1500));
do {
int i;
test_data td;
@ -174,7 +174,7 @@ static void test_mutex_nthread (testing t) {
}
pthread_mutex_destroy (&td.mutex);
loop_count *= 2;
} while (nsync_time_cmp (nsync_time_now (), deadline) < 0);
} while (nsync_time_cmp (nsync_time_now (NSYNC_CLOCK), deadline) < 0);
}
/* void pthread_rwlock_wrlock */
@ -193,7 +193,7 @@ static void void_pthread_rwlock_unlock (void *mu) {
static void test_rwmutex_nthread (testing t) {
int loop_count = 100000;
nsync_time deadline;
deadline = nsync_time_add (nsync_time_now (), nsync_time_ms (1500));
deadline = nsync_time_add (nsync_time_now (NSYNC_CLOCK), nsync_time_ms (1500));
do {
int i;
test_data td;
@ -215,7 +215,7 @@ static void test_rwmutex_nthread (testing t) {
}
pthread_rwlock_destroy (&td.rwmutex);
loop_count *= 2;
} while (nsync_time_cmp (nsync_time_now (), deadline) < 0);
} while (nsync_time_cmp (nsync_time_now (NSYNC_CLOCK), deadline) < 0);
}
/* --------------------------------------- */
@ -246,7 +246,7 @@ static void counting_loop_try_mu (test_data *td, int id) {
static void test_try_mu_nthread (testing t) {
int loop_count = 100000;
nsync_time deadline;
deadline = nsync_time_add (nsync_time_now (), nsync_time_ms (1500));
deadline = nsync_time_add (nsync_time_now (NSYNC_CLOCK), nsync_time_ms (1500));
do {
int i;
test_data td;
@ -266,7 +266,7 @@ static void test_try_mu_nthread (testing t) {
td.n_threads*td.loop_count, td.i));
}
loop_count *= 2;
} while (nsync_time_cmp (nsync_time_now (), deadline) < 0);
} while (nsync_time_cmp (nsync_time_now (NSYNC_CLOCK), deadline) < 0);
}
/* --------------------------------------- */
@ -305,7 +305,7 @@ static int counter_wait_for_zero_with_deadline (counter *c, nsync_time abs_deadl
int value;
nsync_mu_rlock (&c->mu);
while (c->value != 0 &&
nsync_cv_wait_with_deadline (&c->cv, &c->mu, CLOCK_REALTIME, abs_deadline, NULL) == 0) {
nsync_cv_wait_with_deadline (&c->cv, &c->mu, NSYNC_CLOCK, abs_deadline, NULL) == 0) {
}
value = c->value;
nsync_mu_runlock (&c->mu);
@ -429,7 +429,7 @@ static void lock_unlock (testing t, const char *id, int verbose, nsync_mu *mu, i
if (verbose) {
TEST_LOG (t, ("lock_unlock %s incremented value to %d\n", id, *value));
}
nsync_time_sleep (sleep);
nsync_time_sleep (NSYNC_CLOCK, sleep);
nsync_mu_unlock (mu);
counter_inc (done, -1);
}
@ -453,7 +453,7 @@ static void rlock_runlock (testing t, const char *id, int verbose, nsync_mu *mu,
testing_panic (smprintf ("rlock_runlock %s expected "
"value %d, *value=%d", id, expected_value, *value));
}
nsync_time_sleep (sleep);
nsync_time_sleep (NSYNC_CLOCK, sleep);
nsync_mu_runlock (mu);
counter_inc (done, -1);
}
@ -465,7 +465,7 @@ static int check_times (testing t, const char *id, nsync_time start_time,
int exceeds_count = 0;
nsync_time now;
nsync_time measured_duration;
now = nsync_time_now ();
now = nsync_time_now (NSYNC_CLOCK);
measured_duration = nsync_time_sub (now, start_time);
if (nsync_time_cmp (measured_duration,
nsync_time_sub (expected_duration, nsync_time_ms (5))) < 0) {
@ -520,7 +520,7 @@ static void test_rlock (testing t) {
nsync_time start_time;
nsync_mu_init (&mu);
start_time = nsync_time_now ();
start_time = nsync_time_now (NSYNC_CLOCK);
/* ------------------------------------ */
/* Acquire lock with nsync_mu_rtrylock(). This thread will
@ -564,7 +564,7 @@ static void test_rlock (testing t) {
lock_unlock_sleeping, lock_unlock_done));
counter_wait_for_zero (lock_unlock_sleeping);
nsync_time_sleep (delay_duration); /* give time for lock_unlock() thread to wait. */
nsync_time_sleep (NSYNC_CLOCK, delay_duration); /* give time for lock_unlock() thread to wait. */
nsync_mu_rassert_held (&mu);
@ -581,7 +581,7 @@ static void test_rlock (testing t) {
nsync_mu_rassert_held (&mu);
counter_wait_for_zero (rlock_runlock_sleeping);
nsync_time_sleep (delay_duration); /* time for rlock_runlock() threads to wait. */
nsync_time_sleep (NSYNC_CLOCK, delay_duration); /* time for rlock_runlock() threads to wait. */
nsync_mu_rassert_held (&mu);
@ -610,7 +610,7 @@ static void test_rlock (testing t) {
nsync_mu_runlock (&mu);
/* ==================================== */
read_start_time = nsync_time_now ();
read_start_time = nsync_time_now (NSYNC_CLOCK);
counter_wait_for_zero (lock_unlock_done); /* Now can get write lock. */
max_write_wait_exceeded += check_times (t, "i", start_time,
nsync_time_add (nsync_time_add (delay_duration, delay_duration), writer_duration),
@ -656,7 +656,7 @@ static void test_rlock (testing t) {
nsync_time start_time;
nsync_mu_init (&mu);
start_time = nsync_time_now ();
start_time = nsync_time_now (NSYNC_CLOCK);
/* ------------------------------------ */
/* Acquire lock with nsync_mu_trylock(). This thread will hold
@ -696,7 +696,7 @@ static void test_rlock (testing t) {
lock_unlock_sleeping, lock_unlock_done));
counter_wait_for_zero (lock_unlock_sleeping);
nsync_time_sleep (delay_duration); /* give time for lock_unlock() thread to wait. */
nsync_time_sleep (NSYNC_CLOCK, delay_duration); /* give time for lock_unlock() thread to wait. */
nsync_mu_assert_held (&mu);
nsync_mu_rassert_held (&mu);
@ -715,7 +715,7 @@ static void test_rlock (testing t) {
nsync_mu_rassert_held (&mu);
counter_wait_for_zero (rlock_runlock_sleeping);
nsync_time_sleep (delay_duration); /* time for rlock_runlock() threads to wait. */
nsync_time_sleep (NSYNC_CLOCK, delay_duration); /* time for rlock_runlock() threads to wait. */
nsync_mu_assert_held (&mu);
nsync_mu_rassert_held (&mu);
@ -753,7 +753,7 @@ static void test_rlock (testing t) {
nsync_mu_unlock (&mu);
/* ==================================== */
read_start_time = nsync_time_now ();
read_start_time = nsync_time_now (NSYNC_CLOCK);
counter_wait_for_zero (lock_unlock_done); /* Now can get write lock. */
max_write_wait_exceeded += check_times (t, "H", start_time,
nsync_time_add (nsync_time_add (delay_duration, delay_duration), writer_duration),