124 lines
5.5 KiB
C
124 lines
5.5 KiB
C
/*
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* Copyright (c) 2018, Salvatore Sanfilippo <antirez at gmail dot com>
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* All rights reserved.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions are met:
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*
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* * Redistributions of source code must retain the above copyright notice,
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* this list of conditions and the following disclaimer.
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* * Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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* * Neither the name of Redis nor the names of its contributors may be used
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* to endorse or promote products derived from this software without
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* specific prior written permission.
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*
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* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
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* AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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* ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
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* LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
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* CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
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* SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
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* INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
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* CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
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* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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* POSSIBILITY OF SUCH DAMAGE.
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*/
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#include <time.h>
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/* This is a safe version of localtime() which contains no locks and is
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* fork() friendly. Even the _r version of localtime() cannot be used safely
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* in Redis. Another thread may be calling localtime() while the main thread
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* forks(). Later when the child process calls localtime() again, for instance
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* in order to log something to the Redis log, it may deadlock: in the copy
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* of the address space of the forked process the lock will never be released.
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*
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* This function takes the timezone 'tz' as argument, and the 'dst' flag is
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* used to check if daylight saving time is currently in effect. The caller
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* of this function should obtain such information calling tzset() ASAP in the
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* main() function to obtain the timezone offset from the 'timezone' global
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* variable. To obtain the daylight information, if it is currently active or not,
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* one trick is to call localtime() in main() ASAP as well, and get the
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* information from the tm_isdst field of the tm structure. However the daylight
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* time may switch in the future for long running processes, so this information
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* should be refreshed at safe times.
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*
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* Note that this function does not work for dates < 1/1/1970, it is solely
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* designed to work with what time(NULL) may return, and to support Redis
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* logging of the dates, it's not really a complete implementation. */
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static int is_leap_year(time_t year) {
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if (year % 4) return 0; /* A year not divisible by 4 is not leap. */
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else if (year % 100) return 1; /* If div by 4 and not 100 is surely leap. */
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else if (year % 400) return 0; /* If div by 100 *and* not by 400 is not leap. */
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else return 1; /* If div by 100 and 400 is leap. */
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}
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void nolocks_localtime(struct tm *tmp, time_t t, time_t tz, int dst) {
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const time_t secs_min = 60;
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const time_t secs_hour = 3600;
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const time_t secs_day = 3600*24;
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t -= tz; /* Adjust for timezone. */
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t += 3600*dst; /* Adjust for daylight time. */
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time_t days = t / secs_day; /* Days passed since epoch. */
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time_t seconds = t % secs_day; /* Remaining seconds. */
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tmp->tm_isdst = dst;
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tmp->tm_hour = seconds / secs_hour;
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tmp->tm_min = (seconds % secs_hour) / secs_min;
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tmp->tm_sec = (seconds % secs_hour) % secs_min;
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/* 1/1/1970 was a Thursday, that is, day 4 from the POV of the tm structure
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* where sunday = 0, so to calculate the day of the week we have to add 4
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* and take the modulo by 7. */
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tmp->tm_wday = (days+4)%7;
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/* Calculate the current year. */
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tmp->tm_year = 1970;
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while(1) {
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/* Leap years have one day more. */
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time_t days_this_year = 365 + is_leap_year(tmp->tm_year);
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if (days_this_year > days) break;
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days -= days_this_year;
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tmp->tm_year++;
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}
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tmp->tm_yday = days; /* Number of day of the current year. */
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/* We need to calculate in which month and day of the month we are. To do
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* so we need to skip days according to how many days there are in each
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* month, and adjust for the leap year that has one more day in February. */
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int mdays[12] = {31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};
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mdays[1] += is_leap_year(tmp->tm_year);
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tmp->tm_mon = 0;
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while(days >= mdays[tmp->tm_mon]) {
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days -= mdays[tmp->tm_mon];
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tmp->tm_mon++;
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}
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tmp->tm_mday = days+1; /* Add 1 since our 'days' is zero-based. */
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tmp->tm_year -= 1900; /* Surprisingly tm_year is year-1900. */
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}
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#ifdef LOCALTIME_TEST_MAIN
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#include <stdio.h>
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int main(void) {
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/* Obtain timezone and daylight info. */
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tzset(); /* Now 'timezome' global is populated. */
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time_t t = time(NULL);
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struct tm *aux = localtime(&t);
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int daylight_active = aux->tm_isdst;
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struct tm tm;
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char buf[1024];
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nolocks_localtime(&tm,t,timezone,daylight_active);
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strftime(buf,sizeof(buf),"%d %b %H:%M:%S",&tm);
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printf("[timezone: %d, dl: %d] %s\n", (int)timezone, (int)daylight_active, buf);
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}
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#endif
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