experiment with speeding up Time.local #13968
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That benchmark looks including Rather, I feel that this problem should be reported to Apple. #include <stdio.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <time.h>
#include <unistd.h>
void
localtime_benchmark(const char *cond)
{
struct timespec ts, te;
clock_gettime(CLOCK_MONOTONIC , &ts);
for (long n = 0; n < 10000; ++n) {
time_t lt = 1753075380;
struct tm t;
localtime_r(<, &t);
}
clock_gettime(CLOCK_MONOTONIC , &te);
time_t diff = te.tv_sec - ts.tv_sec;
unsigned long ndiff = te.tv_nsec;
if (te.tv_nsec < ts.tv_nsec) {
--diff;
ndiff += 1000000000UL;
}
ndiff -= ts.tv_nsec;
printf("%s: %ld.%.9lu\n", cond, diff, ndiff);
}
int
main(void)
{
localtime_benchmark("non-forked");
pid_t forked = fork();
if (forked) {
int stat;
waitpid(forked, &stat, 0);
}
else {
localtime_benchmark(" forked");
}
return 0;
} |
time.c
Outdated
| /* Days in each month (non-leap year) */ | ||
| static const int days_in_month[12] = {31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31}; | ||
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| /* Check if year is a leap year */ | ||
| static inline int | ||
| is_leap_year(int year) | ||
| { | ||
| return (year % 4 == 0 && year % 100 != 0) || (year % 400 == 0); | ||
| } | ||
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| /* Get days in month, accounting for leap years */ | ||
| static inline int | ||
| get_days_in_month(int year, int month) | ||
| { | ||
| if (month == 2 && is_leap_year(year)) { | ||
| return 29; | ||
| } | ||
| return days_in_month[month - 1]; | ||
| } | ||
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| /* Calculate day of week from year/month/day */ | ||
| static int | ||
| calculate_wday(int year, int month, int day) | ||
| { | ||
| /* Zeller's congruence algorithm */ | ||
| if (month < 3) { | ||
| month += 12; | ||
| year--; | ||
| } | ||
| int k = year % 100; | ||
| int j = year / 100; | ||
| int h = (day + (13 * (month + 1)) / 5 + k + k / 4 + j / 4 - 2 * j) % 7; | ||
| /* Convert to tm_wday format (Sunday = 0) */ | ||
| return (h + 6) % 7; | ||
| } | ||
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| /* Calculate day of year from year/month/day */ | ||
| static int | ||
| calculate_yday(int year, int month, int day) | ||
| { | ||
| int yday = 0; | ||
| for (int m = 1; m < month; m++) { | ||
| yday += get_days_in_month(year, m); | ||
| } | ||
| return yday + day - 1; /* tm_yday is 0-based */ | ||
| } |
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These look like duplicates to the existing functions.
Indeed. I did some searching around and found a few references which make me think this won't be fixed: https://developer.apple.com/forums/thread/747499 And from fork's manpage:
AIUI there is IPC signaling in place to notify processes of timezone changes, and these don't work after fork() before exec(). |
On macOS, methods like
Time.localcan be up to hundreds of times slower when run in a forked child process than when run in the parent process. This simple benchmark demonstrates the issue:ruby 3.4.3 (2025-04-14 revision d0b7e5b6a0) +PRISM [arm64-darwin20] Warming up -------------------------------------- non-forked 7.873k i/100ms forked 131.000 i/100ms Calculating ------------------------------------- non-forked 77.203k (± 1.0%) i/s (12.95 μs/i) - 393.650k in 5.099458s forked 1.248k (± 2.1%) i/s (801.54 μs/i) - 6.288k in 5.042401s Comparison: non-forked: 77202.9 i/s forked: 1247.6 i/s - 61.88x slowerThis impacts all kinds of things from logging, parsing times, working with zipfiles with
rubyzip, etc.This PR implements a small cache for offsets from UTC for any given 15-minute quarters derived from the value passed to
rb_localtime_r- this avoids multiple calls to libc'slocaltime_rfor the same time values within the same 15-minute block of time. As far as I can tell there are no timezones past or present which have an offset that doesn't fall on a 15-minute boundary (e.g. +0/15/30/45 minutes).The cache is cleared if the timezone is changed.