1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
|
/*
* Copyright (c) 2018, Salvatore Sanfilippo <antirez at gmail dot com>
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are met:
*
* * Redistributions of source code must retain the above copyright notice,
* this list of conditions and the following disclaimer.
* * Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
* * Neither the name of Redis nor the names of its contributors may be used
* to endorse or promote products derived from this software without
* specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
* AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
* LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
* CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
* SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
* INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
* CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
* POSSIBILITY OF SUCH DAMAGE.
*/
#include <time.h>
/* This is a safe version of localtime() which contains no locks and is
* fork() friendly. Even the _r version of localtime() cannot be used safely
* in Redis. Another thread may be calling localtime() while the main thread
* forks(). Later when the child process calls localtime() again, for instance
* in order to log something to the Redis log, it may deadlock: in the copy
* of the address space of the forked process the lock will never be released.
*
* This function takes the timezone 'tz' as argument, and the 'dst' flag is
* used to check if daylight saving time is currently in effect. The caller
* of this function should obtain such information calling tzset() ASAP in the
* main() function to obtain the timezone offset from the 'timezone' global
* variable. To obtain the daylight information, if it is currently active or not,
* one trick is to call localtime() in main() ASAP as well, and get the
* information from the tm_isdst field of the tm structure. However the daylight
* time may switch in the future for long running processes, so this information
* should be refreshed at safe times.
*
* Note that this function does not work for dates < 1/1/1970, it is solely
* designed to work with what time(NULL) may return, and to support Redis
* logging of the dates, it's not really a complete implementation. */
static int is_leap_year(time_t year) {
if (year % 4) return 0; /* A year not divisible by 4 is not leap. */
else if (year % 100) return 1; /* If div by 4 and not 100 is surely leap. */
else if (year % 400) return 0; /* If div by 100 *and* not by 400 is not leap. */
else return 1; /* If div by 100 and 400 is leap. */
}
void nolocks_localtime(struct tm *tmp, time_t t, time_t tz, int dst) {
const time_t secs_min = 60;
const time_t secs_hour = 3600;
const time_t secs_day = 3600*24;
t -= tz; /* Adjust for timezone. */
t += 3600*dst; /* Adjust for daylight time. */
time_t days = t / secs_day; /* Days passed since epoch. */
time_t seconds = t % secs_day; /* Remaining seconds. */
tmp->tm_isdst = dst;
tmp->tm_hour = seconds / secs_hour;
tmp->tm_min = (seconds % secs_hour) / secs_min;
tmp->tm_sec = (seconds % secs_hour) % secs_min;
/* 1/1/1970 was a Thursday, that is, day 4 from the POV of the tm structure
* where sunday = 0, so to calculate the day of the week we have to add 4
* and take the modulo by 7. */
tmp->tm_wday = (days+4)%7;
/* Calculate the current year. */
tmp->tm_year = 1970;
while(1) {
/* Leap years have one day more. */
time_t days_this_year = 365 + is_leap_year(tmp->tm_year);
if (days_this_year > days) break;
days -= days_this_year;
tmp->tm_year++;
}
tmp->tm_yday = days; /* Number of day of the current year. */
/* We need to calculate in which month and day of the month we are. To do
* so we need to skip days according to how many days there are in each
* month, and adjust for the leap year that has one more day in February. */
int mdays[12] = {31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};
mdays[1] += is_leap_year(tmp->tm_year);
tmp->tm_mon = 0;
while(days >= mdays[tmp->tm_mon]) {
days -= mdays[tmp->tm_mon];
tmp->tm_mon++;
}
tmp->tm_mday = days+1; /* Add 1 since our 'days' is zero-based. */
tmp->tm_year -= 1900; /* Surprisingly tm_year is year-1900. */
}
#ifdef LOCALTIME_TEST_MAIN
#include <stdio.h>
int main(void) {
/* Obtain timezone and daylight info. */
tzset(); /* Now 'timezone' global is populated. */
time_t t = time(NULL);
struct tm *aux = localtime(&t);
int daylight_active = aux->tm_isdst;
struct tm tm;
char buf[1024];
nolocks_localtime(&tm,t,timezone,daylight_active);
strftime(buf,sizeof(buf),"%d %b %H:%M:%S",&tm);
printf("[timezone: %d, dl: %d] %s\n", (int)timezone, (int)daylight_active, buf);
}
#endif
|
