Add Redis source code for testing

1 files changed, 103 insertions, 0 deletions

diff --git a/examples/redis-unstable/src/localtime.c b/examples/redis-unstable/src/localtime.c
new file mode 100644
index 0000000..e95eb69
--- /dev/null
+++ b/examples/redis-unstable/src/localtime.c
@@ -0,0 +1,103 @@
+/*
+ * Copyright (c) 2018-Present, Redis Ltd.
+ * All rights reserved.
+ *
+ * Licensed under your choice of (a) the Redis Source Available License 2.0
+ * (RSALv2); or (b) the Server Side Public License v1 (SSPLv1); or (c) the
+ * GNU Affero General Public License v3 (AGPLv3).
+ */
+
+#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