nginx源码阅读-ngx_times.c时间管理
此处记录一下在看ngx_times.c时的随手写下的注释。
/*
* Copyright (C) Igor Sysoev
*/
#include <ngx_config.h>
#include <ngx_core.h>
/*
* The time may be updated by signal handler or by several threads.
* The time update operations are rare and require to hold the ngx_time_lock.
* The time read operations are frequent, so they are lock-free and get time
* values and strings from the current slot. Thus thread may get the corrupted
* values only if it is preempted while copying and then it is not scheduled
* to run more than NGX_TIME_SLOTS seconds.
*/
//k 上面最后一句没看明白，时间读多，写少。如果出现冲突，肯定是中间抢占了并且NGX_TIME_SLOTS秒还没有开始运行
//k 我明白了，这里采用双缓冲的超级版本，64缓冲机制，时间的字符串值采用64秒一个轮回，
//k 通过下面的ngx_cached_*变量直接访问，而不是通过cached_err_log_time[slot]进行索引访问。这样冲突的概率非常小，64秒内还没有调度运行，才有可能。
//k 不过其实咱们能想到，取错误日志时间，正常时间，三者还是可能出现一秒的误差，不过这是在一秒的开始，结束，没啥关系的
#define NGX_TIME_SLOTS 64
static ngx_uint_t slot;
static ngx_atomic_t ngx_time_lock;//k 这锁高效啊，一个整数
volatile ngx_msec_t ngx_current_msec;
volatile ngx_time_t *ngx_cached_time;
volatile ngx_str_t ngx_cached_err_log_time;
volatile ngx_str_t ngx_cached_http_time;
volatile ngx_str_t ngx_cached_http_log_time;
#if !(NGX_WIN32)
/*
* locatime() and localtime_r() are not Async-Signal-Safe functions, therefore,
* they must not be called by a signal handler, so we use the cached
* GMT offset value. Fortunately the value is changed only two times a year.
*/
static ngx_int_t cached_gmtoff;
#endif
static ngx_time_t cached_time[NGX_TIME_SLOTS];
static u_char cached_err_log_time[NGX_TIME_SLOTS]
[sizeof("1970/09/28 12:00:00")];
static u_char cached_http_time[NGX_TIME_SLOTS]
[sizeof("Mon, 28 Sep 1970 06:00:00 GMT")];
static u_char cached_http_log_time[NGX_TIME_SLOTS]
[sizeof("28/Sep/1970:12:00:00 +0600")];
static char *week[] = { "Sun", "Mon", "Tue", "Wed", "Thu", "Fri", "Sat" };
static char *months[] = { "Jan", "Feb", "Mar", "Apr", "May", "Jun",
"Jul", "Aug", "Sep", "Oct", "Nov", "Dec" };
void
ngx_time_init(void)
{
ngx_cached_err_log_time.len = sizeof("1970/09/28 12:00:00") - 1;
ngx_cached_http_time.len = sizeof("Mon, 28 Sep 1970 06:00:00 GMT") - 1;
ngx_cached_http_log_time.len = sizeof("28/Sep/1970:12:00:00 +0600") - 1;
ngx_cached_time = &cached_time[0];
ngx_time_update();
}
/*k
ngx_master_process_cycle会每次处理完信号后调用这里；
ngx_epoll_process_events如果设置了ngx_timer_resolution也会定期掉这里，这个是配置精确时间时用的
*/
void
ngx_time_update(void)
{
u_char *p0, *p1, *p2;
ngx_tm_t tm, gmt;//k struct tm
time_t sec;
ngx_uint_t msec;
ngx_time_t *tp;
struct timeval tv;
if (!ngx_trylock(&ngx_time_lock)) {
return;//k 如果没拿到锁，那给力，有人在更新呢
}
ngx_gettimeofday(&tv);//k gettimeofday(tp, NULL);
sec = tv.tv_sec;
msec = tv.tv_usec / 1000;
ngx_current_msec = (ngx_msec_t) sec * 1000 + msec;//k 当前的毫秒数，可以立即更新
tp = &cached_time[slot];//k 引用全局的缓存时间slot位置
if (tp->sec == sec) {
//k 秒数相等，就只更新毫秒数了，其他不动，那其他时间值呢，因为下面的字符串值压根就不需要毫秒数，所以咱们可以直接退出啦
tp->msec = msec;
ngx_unlock(&ngx_time_lock);
return;
}
if (slot == NGX_TIME_SLOTS - 1) {//k 不断轮询这个cached_time结构，到头了回0
slot = 0;//k 这里就加1了，那其他线程读取这个值，怎么办?，我还没更新完呢，你们怎么也得取上一个吧
} else {
slot++;
}
tp = &cached_time[slot];//k 指向下一个槽位
tp->sec = sec;//k 更新新的槽位的时间，让他等于最新的时间
tp->msec = msec;
ngx_gmtime(sec, &gmt);//k 搞一个字符串型的时间值用用
p0 = &cached_http_time[slot][0];
(void) ngx_sprintf(p0, "%s, %02d %s %4d %02d:%02d:%02d GMT",
week[gmt.ngx_tm_wday], gmt.ngx_tm_mday,
months[gmt.ngx_tm_mon - 1], gmt.ngx_tm_year,
gmt.ngx_tm_hour, gmt.ngx_tm_min, gmt.ngx_tm_sec);
#if (NGX_HAVE_GETTIMEZONE)
tp->gmtoff = ngx_gettimezone();
ngx_gmtime(sec + tp->gmtoff * 60, &tm);
#elif (NGX_HAVE_GMTOFF)
ngx_localtime(sec, &tm);
cached_gmtoff = (ngx_int_t) (tm.ngx_tm_gmtoff / 60);
tp->gmtoff = cached_gmtoff;
#else
ngx_localtime(sec, &tm);
cached_gmtoff = ngx_timezone(tm.ngx_tm_isdst);
tp->gmtoff = cached_gmtoff;
#endif
//k 更新错误日志的时间值
p1 = &cached_err_log_time[slot][0];
(void) ngx_sprintf(p1, "%4d/%02d/%02d %02d:%02d:%02d",
tm.ngx_tm_year, tm.ngx_tm_mon,
tm.ngx_tm_mday, tm.ngx_tm_hour,
tm.ngx_tm_min, tm.ngx_tm_sec);
p2 = &cached_http_log_time[slot][0];
(void) ngx_sprintf(p2, "%02d/%s/%d:%02d:%02d:%02d %c%02d%02d",
tm.ngx_tm_mday, months[tm.ngx_tm_mon - 1],
tm.ngx_tm_year, tm.ngx_tm_hour,
tm.ngx_tm_min, tm.ngx_tm_sec,
tp->gmtoff < 0 ? '-' : '+',
ngx_abs(tp->gmtoff / 60), ngx_abs(tp->gmtoff % 60));
ngx_memory_barrier();//k 这个作用是啥 ?
//k 作用是，如果不加这个，编译器可能会将p1,p2,p3本来是123123的方式排列，优化为112233的方式，从而，应用程序读取的时间发生冲突的概率更大了。妙!
//k 到这里才正式更新，更新后，其他地方就可以通过下面的结构直接访问到了，不用通过数组，slot来访问。相当于上面printf更新的时候，其他线程还是访问不到的
//k 这里相当于数组时用来做双缓冲的超级版本，64缓冲用的，64秒一个轮回，这样保证正常情况下，不会出现串了的情况
//k 不过还是有个小注意点，比如我先打一条ngx_cached_http_time日志，然后一条ngx_cached_http_log_time到文件中，然后发现，前面一条是10秒的时候，后面一条却是9秒，穿越了
//k 因为下面的四条的更新不是原子操作
ngx_cached_time = tp;
ngx_cached_http_time.data = p0;
ngx_cached_err_log_time.data = p1;
ngx_cached_http_log_time.data = p2;
ngx_unlock(&ngx_time_lock);
}
#if !(NGX_WIN32)
void
ngx_time_sigsafe_update(void)
{//k 这个函数只更新cached_err_log_time时间,只在ngx_signal_handler里面用过,收到信号的时候
//k 取得最新时间，不是通过缓存的时间取的。但设置到了缓存的里面了，而且把slot增加了
u_char *p;
ngx_tm_t tm;
time_t sec;
ngx_time_t *tp;
struct timeval tv;
if (!ngx_trylock(&ngx_time_lock)) {
return;
}
ngx_gettimeofday(&tv);
sec = tv.tv_sec;
tp = &cached_time[slot];
if (tp->sec == sec) {//k 如果秒数相等，不用更新啥的。这样一秒内多个信号，不会重复更新，凭白白费多个slot
ngx_unlock(&ngx_time_lock);
return;
}
if (slot == NGX_TIME_SLOTS - 1) {
slot = 0;
} else {//k 增加一个新的槽位，但是却不更新&cached_time[slot]处的时间值，而至更新cached_err_log_time时间，你明知道它有更新
//k 这样我一秒给你来600个信号，第一个你这样走了，然后新的slot的时间必然是64秒之前的，然后你以为时间不对，然后就又去增加slot···
slot++;
}
//k 信号处理调用这个函数却没有像下面一样更新当前最新槽位的时间,
//k 这样迫使在下次ngx_time_update的时候看这个槽位上还是64秒之前的那个时间，于是将slot增加1，放入下一个。这样这个槽位就相当于白费了。
//tp->sec = sec;//k 更新新的槽位的时间，让他等于最新的时间
/*k 上面这行曾经有个bug,见这里:http://forum.nginx.org/read.php?29,231001
*) Fixed possible use of old cached times if runtime went backwards.
If ngx_time_sigsafe_update() updated only ngx_cached_err_log_time, and
then clock was adjusted backwards, the cached_time[slot].sec might
accidentally match current seconds on next ngx_time_update() call,
resulting in various cached times not being updated.
Fix is to clear the cached_time[slot].sec to explicitly mark cached times
are stale and need updating.
*/
ngx_gmtime(sec + cached_gmtoff * 60, &tm);
p = &cached_err_log_time[slot][0];
(void) ngx_sprintf(p, "%4d/%02d/%02d %02d:%02d:%02d",
tm.ngx_tm_year, tm.ngx_tm_mon,
tm.ngx_tm_mday, tm.ngx_tm_hour,
tm.ngx_tm_min, tm.ngx_tm_sec);
ngx_memory_barrier();
//k 其实在这里我们知道，ngx_cached_* 这几个变量，不一定是一一的对应到对应的数组的slot位置，一旦掉了这个函数，ngx_cached_err_log_time就指向最新的slot处；
//k 但其他却指向前一个，然后等ngx_time_update调用后，全都指向再下一个，相当于一个信号让他们跳级了
ngx_cached_err_log_time.data = p;
ngx_unlock(&ngx_time_lock);
}
#endif
u_char *
ngx_http_time(u_char *buf, time_t t)
{
ngx_tm_t tm;
ngx_gmtime(t, &tm);
return ngx_sprintf(buf, "%s, %02d %s %4d %02d:%02d:%02d GMT",
week[tm.ngx_tm_wday],
tm.ngx_tm_mday,
months[tm.ngx_tm_mon - 1],
tm.ngx_tm_year,
tm.ngx_tm_hour,
tm.ngx_tm_min,
tm.ngx_tm_sec);
}
u_char *
ngx_http_cookie_time(u_char *buf, time_t t)
{
ngx_tm_t tm;
ngx_gmtime(t, &tm);
/*
* Netscape 3.x does not understand 4-digit years at all and
* 2-digit years more than "37"
*/
return ngx_sprintf(buf,
(tm.ngx_tm_year > 2037) ?
"%s, %02d-%s-%d %02d:%02d:%02d GMT":
"%s, %02d-%s-%02d %02d:%02d:%02d GMT",
week[tm.ngx_tm_wday],
tm.ngx_tm_mday,
months[tm.ngx_tm_mon - 1],
(tm.ngx_tm_year > 2037) ? tm.ngx_tm_year:
tm.ngx_tm_year % 100,
tm.ngx_tm_hour,
tm.ngx_tm_min,
tm.ngx_tm_sec);
}
void
ngx_gmtime(time_t t, ngx_tm_t *tp)
{
ngx_int_t yday;
ngx_uint_t n, sec, min, hour, mday, mon, year, wday, days, leap;
/* the calculation is valid for positive time_t only */
n = (ngx_uint_t) t;
days = n / 86400;
/* Jaunary 1, 1970 was Thursday */
wday = (4 + days) % 7;
n %= 86400;
hour = n / 3600;
n %= 3600;
min = n / 60;
sec = n % 60;
/*
* the algorithm based on Gauss' formula,
* see src/http/ngx_http_parse_time.c
*/
/* days since March 1, 1 BC */
days = days - (31 + 28) + 719527;
/*
* The "days" should be adjusted to 1 only, however, some March 1st's go
* to previous year, so we adjust them to 2. This causes also shift of the
* last Feburary days to next year, but we catch the case when "yday"
* becomes negative.
*/
year = (days + 2) * 400 / (365 * 400 + 100 - 4 + 1);
yday = days - (365 * year + year / 4 - year / 100 + year / 400);
if (yday < 0) {
leap = (year % 4 == 0) && (year % 100 || (year % 400 == 0));
yday = 365 + leap + yday;
year--;
}
/*
* The empirical formula that maps "yday" to month.
* There are at least 10 variants, some of them are:
* mon = (yday + 31) * 15 / 459
* mon = (yday + 31) * 17 / 520
* mon = (yday + 31) * 20 / 612
*/
mon = (yday + 31) * 10 / 306;
/* the Gauss' formula that evaluates days before the month */
mday = yday - (367 * mon / 12 - 30) + 1;
if (yday >= 306) {
year++;
mon -= 10;
/*
* there is no "yday" in Win32 SYSTEMTIME
*
* yday -= 306;
*/
} else {
mon += 2;
/*
* there is no "yday" in Win32 SYSTEMTIME
*
* yday += 31 + 28 + leap;
*/
}
tp->ngx_tm_sec = (ngx_tm_sec_t) sec;
tp->ngx_tm_min = (ngx_tm_min_t) min;
tp->ngx_tm_hour = (ngx_tm_hour_t) hour;
tp->ngx_tm_mday = (ngx_tm_mday_t) mday;
tp->ngx_tm_mon = (ngx_tm_mon_t) mon;
tp->ngx_tm_year = (ngx_tm_year_t) year;
tp->ngx_tm_wday = (ngx_tm_wday_t) wday;
}
time_t
ngx_next_time(time_t when)
{
time_t now, next;
struct tm tm;
now = ngx_time();
ngx_libc_localtime(now, &tm);
tm.tm_hour = (int) (when / 3600);
when %= 3600;
tm.tm_min = (int) (when / 60);
tm.tm_sec = (int) (when % 60);
next = mktime(&tm);
if (next == -1) {
return -1;
}
if (next - now > 0) {
return next;
}
tm.tm_mday++;
/* mktime() should normalize a date (Jan 32, etc) */
next = mktime(&tm);
if (next != -1) {
return next;
}
return -1;
}
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