redis时间事件

数据结构

文件：ae.h

时间事件的三个属性：

when ：以毫秒格式的 UNIX 时间戳为单位，记录了应该在什么时间点执行事件处理函数。

timeProc ：事件处理函数。

next 指向下一个时间事件，形成链表。

/* Time event structure */
typedef struct aeTimeEvent {
long long id; /* time event identifier. */
long when_sec; /* seconds */
long when_ms; /* milliseconds */
aeTimeProc *timeProc;
aeEventFinalizerProc *finalizerProc;
void *clientData;
struct aeTimeEvent *next;
} aeTimeEvent;

api

文件：ae.c(v3.0.1 L 203)

函数 aeCreateTimeEvent

long long aeCreateTimeEvent(aeEventLoop *eventLoop, long long milliseconds,
aeTimeProc *proc, void *clientData,
aeEventFinalizerProc *finalizerProc)
{
long long id = eventLoop->timeEventNextId++;
aeTimeEvent *te;

te = zmalloc(sizeof(*te));
if (te == NULL) return AE_ERR;
te->id = id;
aeAddMillisecondsToNow(milliseconds,&te->when_sec,&te->when_ms);
te->timeProc = proc;
te->finalizerProc = finalizerProc;
te->clientData = clientData;
te->next = eventLoop->timeEventHead;
eventLoop->timeEventHead = te;
return id;
}

示例serverCron 使用

redis-server启动时，Redis做了很多初始化的工作，这些工作大多是在initServer()这个函数中执行的，初始化一些相关的list,dict等；调用了aeCreateTimeEvent()函数来初始化一下定时器，定期地执行serverCron()这个函数。

文件redis.c(v3.0.1 L1837)

/* Create the serverCron() time event, that's our main way to process
* background operations. */
if(aeCreateTimeEvent(server.el, 1, serverCron, NULL, NULL) == AE_ERR) {
redisPanic("Can't create the serverCron time event.");
exit(1);
}

触发定时任务执行

整个执行流程：

main->aeMain->aeProcessEvents->processTimeEvents->serverCron

文件: ae.c

/* Process time events */
static int processTimeEvents(aeEventLoop *eventLoop) {
int processed = 0;
aeTimeEvent *te;
long long maxId;
time_t now = time(NULL);

/* If the system clock is moved to the future, and then set back to the
* right value, time events may be delayed in a random way. Often this
* means that scheduled operations will not be performed soon enough.
*
* Here we try to detect system clock skews, and force all the time
* events to be processed ASAP when this happens: the idea is that
* processing events earlier is less dangerous than delaying them
* indefinitely, and practice suggests it is. */
if (now < eventLoop->lastTime) {
te = eventLoop->timeEventHead;
while(te) {
te->when_sec = 0;
te = te->next;
}
}
eventLoop->lastTime = now;

te = eventLoop->timeEventHead;
maxId = eventLoop->timeEventNextId-1;
while(te) {
long now_sec, now_ms;
long long id;

if (te->id > maxId) {
te = te->next;
continue;
}
aeGetTime(&now_sec, &now_ms);
if (now_sec > te->when_sec ||
(now_sec == te->when_sec && now_ms >= te->when_ms))
{
int retval;

id = te->id;
retval = te->timeProc(eventLoop, id, te->clientData);
processed++;
/* After an event is processed our time event list may
* no longer be the same, so we restart from head.
* Still we make sure to don't process events registered
* by event handlers itself in order to don't loop forever.
* To do so we saved the max ID we want to handle.
*
* FUTURE OPTIMIZATIONS:
* Note that this is NOT great algorithmically. Redis uses
* a single time event so it's not a problem but the right
* way to do this is to add the new elements on head, and
* to flag deleted elements in a special way for later
* deletion (putting references to the nodes to delete into
* another linked list). */
if (retval != AE_NOMORE) {
aeAddMillisecondsToNow(retval,&te->when_sec,&te->when_ms);
} else {
aeDeleteTimeEvent(eventLoop, id);
}
te = eventLoop->timeEventHead;
} else {
te = te->next;
}
}
return processed;

根据 timeProc 函数的返回值，可以将时间事件划分为两类：

如果事件处理函数返回 ae.h/AE_NOMORE ，那么这个事件为单次执行事件：该事件会在指定的时间被处理一次，之后该事件就会被删除，不再执行。

如果事件处理函数返回一个非 AE_NOMORE 的整数值，那么这个事件为循环执行事件：该事件会在指定的时间被处理，之后它会按照事件处理函数的返回值，更新事件的 when 属性，让这个事件在之后的某个时间点再次运行，并以这种方式一直更新并运行下去。