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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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35
third_party/nsync/testing/cv_test.c vendored
View file

@ -29,7 +29,6 @@
#include "third_party/nsync/testing/smprintf.h"
#include "third_party/nsync/testing/testing.h"
#include "third_party/nsync/testing/time_extra.h"
#include "libc/sysv/consts/clock.h"
#include "third_party/nsync/time.h"
/* --------------------------- */
@ -64,7 +63,7 @@ static int cv_queue_put (cv_queue *q, void *v, nsync_time abs_deadline) {
int wake = 0;
nsync_mu_lock (&q->mu);
while (q->count == q->limit &&
nsync_cv_wait_with_deadline (&q->non_full, &q->mu, CLOCK_REALTIME, abs_deadline, NULL) == 0) {
nsync_cv_wait_with_deadline (&q->non_full, &q->mu, NSYNC_CLOCK, abs_deadline, NULL) == 0) {
}
if (q->count != q->limit) {
int i = q->pos + q->count;
@ -92,7 +91,7 @@ static void *cv_queue_get (cv_queue *q, nsync_time abs_deadline) {
void *v = NULL;
nsync_mu_lock (&q->mu);
while (q->count == 0 &&
nsync_cv_wait_with_deadline (&q->non_empty, &q->mu, CLOCK_REALTIME, abs_deadline, NULL) == 0) {
nsync_cv_wait_with_deadline (&q->non_empty, &q->mu, NSYNC_CLOCK, abs_deadline, NULL) == 0) {
}
if (q->count != 0) {
v = q->data[q->pos];
@ -236,13 +235,13 @@ static void test_cv_deadline (testing t) {
nsync_time end_time;
nsync_time start_time;
nsync_time expected_end_time;
start_time = nsync_time_now ();
start_time = nsync_time_now (NSYNC_CLOCK);
expected_end_time = nsync_time_add (start_time, nsync_time_ms (87));
if (nsync_cv_wait_with_deadline (&cv, &mu, CLOCK_REALTIME, expected_end_time,
if (nsync_cv_wait_with_deadline (&cv, &mu, NSYNC_CLOCK, expected_end_time,
NULL) != ETIMEDOUT) {
TEST_FATAL (t, ("nsync_cv_wait() returned non-expired for a timeout"));
}
end_time = nsync_time_now ();
end_time = nsync_time_now (NSYNC_CLOCK);
if (nsync_time_cmp (end_time, nsync_time_sub (expected_end_time, too_early)) < 0) {
char *elapsed_str = nsync_time_str (nsync_time_sub (expected_end_time, end_time), 2);
TEST_ERROR (t, ("nsync_cv_wait() returned %s too early", elapsed_str));
@ -275,7 +274,7 @@ static void test_cv_cancel (testing t) {
/* The loops below cancel after 87 milliseconds, like the timeout tests above. */
future_time = nsync_time_add (nsync_time_now (), nsync_time_ms (3600000)); /* test cancels with timeout */
future_time = nsync_time_add (nsync_time_now (NSYNC_CLOCK), nsync_time_ms (3600000)); /* test cancels with timeout */
too_late_violations = 0;
nsync_mu_lock (&mu);
@ -285,18 +284,18 @@ static void test_cv_cancel (testing t) {
nsync_time end_time;
nsync_time start_time;
nsync_time expected_end_time;
start_time = nsync_time_now ();
start_time = nsync_time_now (NSYNC_CLOCK);
expected_end_time = nsync_time_add (start_time, nsync_time_ms (87));
cancel = nsync_note_new (NULL, expected_end_time);
cancel = nsync_note_new (NULL, NSYNC_CLOCK, expected_end_time);
x = nsync_cv_wait_with_deadline (&cv, &mu, CLOCK_REALTIME, future_time, cancel);
x = nsync_cv_wait_with_deadline (&cv, &mu, NSYNC_CLOCK, future_time, cancel);
if (x != ECANCELED) {
TEST_FATAL (t, ("nsync_cv_wait() returned non-cancelled (%d) for "
"a cancellation; expected %d",
x, ECANCELED));
}
end_time = nsync_time_now ();
end_time = nsync_time_now (NSYNC_CLOCK);
if (nsync_time_cmp (end_time, nsync_time_sub (expected_end_time, too_early)) < 0) {
char *elapsed_str = nsync_time_str (nsync_time_sub (expected_end_time, end_time), 2);
TEST_ERROR (t, ("nsync_cv_wait() returned %s too early", elapsed_str));
@ -307,15 +306,15 @@ static void test_cv_cancel (testing t) {
}
/* Check that an already cancelled wait returns immediately. */
start_time = nsync_time_now ();
start_time = nsync_time_now (NSYNC_CLOCK);
x = nsync_cv_wait_with_deadline (&cv, &mu, CLOCK_REALTIME, nsync_time_no_deadline, cancel);
x = nsync_cv_wait_with_deadline (&cv, &mu, NSYNC_CLOCK, nsync_time_no_deadline, cancel);
if (x != ECANCELED) {
TEST_FATAL (t, ("nsync_cv_wait() returned non-cancelled (%d) for "
"a cancellation; expected %d",
x, ECANCELED));
}
end_time = nsync_time_now ();
end_time = nsync_time_now (NSYNC_CLOCK);
if (nsync_time_cmp (end_time, start_time) < 0) {
char *elapsed_str = nsync_time_str (nsync_time_sub (expected_end_time, end_time), 2);
TEST_ERROR (t, ("nsync_cv_wait() returned %s too early", elapsed_str));
@ -522,7 +521,7 @@ static void test_cv_debug (testing t) {
closure_fork (closure_debug_thread (&debug_thread_writer_cv, s));
closure_fork (closure_debug_thread (&debug_thread_writer_cv, s));
closure_fork (closure_debug_thread_reader (&debug_thread_reader_cv, s, NULL));
nsync_time_sleep (nsync_time_ms (500));
nsync_time_sleep (NSYNC_CLOCK, nsync_time_ms (500));
*slot (s, "wait0_mu") = nsync_mu_debug_state_and_waiters (
&s->mu, (char *) malloc (len), len);
*slot (s, "wait0_cv") = nsync_cv_debug_state_and_waiters (
@ -530,7 +529,7 @@ static void test_cv_debug (testing t) {
/* allow the threads to proceed to their conditional waits */
nsync_mu_unlock (&s->mu);
nsync_time_sleep (nsync_time_ms (500));
nsync_time_sleep (NSYNC_CLOCK, nsync_time_ms (500));
*slot (s, "wait1_mu") = nsync_mu_debug_state_and_waiters (
&s->mu, (char *) malloc (len), len);
*slot (s, "wait1_cv") = nsync_cv_debug_state_and_waiters (
@ -547,7 +546,7 @@ static void test_cv_debug (testing t) {
/* allow all threads to proceed and exit */
s->flag = 0;
nsync_mu_unlock (&s->mu);
nsync_time_sleep (nsync_time_ms (500));
nsync_time_sleep (NSYNC_CLOCK, nsync_time_ms (500));
*slot (s, "wait3_mu") = nsync_mu_debug_state_and_waiters (
&s->mu, (char *) malloc (len), len);
*slot (s, "wait3_cv") = nsync_cv_debug_state_and_waiters (
@ -559,7 +558,7 @@ static void test_cv_debug (testing t) {
&s->mu, (char *) malloc (len), len);
closure_fork (closure_debug_thread_reader (
&debug_thread_reader, s, "rheld2_mu"));
nsync_time_sleep (nsync_time_ms (500));
nsync_time_sleep (NSYNC_CLOCK, nsync_time_ms (500));
*slot (s, "rheld1again_mu") = nsync_mu_debug_state_and_waiters (
&s->mu, (char *) malloc (len), len);
nsync_mu_runlock (&s->mu);