[原]Redis源代码分析之七：事件驱动库分析
aeEventLoop是一个记录记录程序事件状态的结构：/* State of an event based program */typedef struct aeEventLoop {
int maxfd;
long long timeEventNextId;
aeFileEvent events; /* Registered events */
aeFiredEvent fired; /* Fired events */
aeTimeEvent *timeEventHead;
int stop;
void *apidata; /* This is used for polling API specific data */
aeBeforeSleepProc *beforesleep;
} aeEventLoop;
该结构在aeCreateEventLoop()函数中得到初始化。
EventLoop中的事件类型包括时间事件：
/* 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;
以及文件事件：
/* File event structure */
typedef struct aeFileEvent {
int mask; /* one of AE_(READABLE|WRITABLE) */
aeFileProc *rfileProc;
aeFileProc *wfileProc;
void *clientData;
} aeFileEvent;
分别在aeCreateTimeEvent函数和aeCreateTimeEvent函数中得到初始化。
当事件循环EventLoop结构在initServer()中创建并初始化完成之后，主函数就调用aeMain()函数开始处理事件：
void aeMain(aeEventLoop *eventLoop) {
eventLoop->stop = 0;
while (!eventLoop->stop) {
if (eventLoop->beforesleep != NULL)
eventLoop->beforesleep(eventLoop);
aeProcessEvents(eventLoop, AE_ALL_EVENTS);
}
}
我们看到，只要eventLoop结构中停止处理的标识stop不为1，事件循环就不断地调用aeProcessEvents来处理事件。
int aeProcessEvents(aeEventLoop *eventLoop, int flags);
该函数处理每个待处理的时间事件和文件事件，传入的flag决定处理的方式：
* If flags is 0, the function does nothing and returns.
* if flags has AE_ALL_EVENTS set, all the kind of events are processed.
* if flags has AE_FILE_EVENTS set, file events are processed.
* if flags has AE_TIME_EVENTS set, time events are processed.
* if flags has AE_DONT_WAIT set the function returns ASAP until all
* the events that's possible to process without to wait are processed.
函数返回完成处理的事件的数量。
函数首先调用aeSearchNearestTimer函数选择最近要fire的计时器，然后更新tvp，这一步不展开。
在函数中，调用aeApiPoll来监控事件，该函数封装了select、kqueue、epoll三种机制：
numevents = aeApiPoll(eventLoop, tvp);
在select模型下，实现为：
retval = select(eventLoop->maxfd+1,
&state->_rfds,&state->_wfds,NULL,tvp);
在kqueue模型下，实现为：
if (tvp != NULL) {
struct timespec timeout;
timeout.tv_sec = tvp->tv_sec;
timeout.tv_nsec = tvp->tv_usec * 1000;
retval = kevent(state->kqfd, NULL, 0, state->events, AE_SETSIZE, &timeout);
} else {
retval = kevent(state->kqfd, NULL, 0, state->events, AE_SETSIZE, NULL);
}
在epoll模型下，实现为：
retval = epoll_wait(state->epfd,state->events,AE_SETSIZE,
tvp ? (tvp->tv_sec*1000 + tvp->tv_usec/1000) : -1);
关于这三种处理机制的分析比较可以参考：http://www.kegel.com/c10k.html
完成事件的监控调度之后，把这些事件加入eventLoop的fired记录中，然后返回numevents：
if (retval > 0) {
int j;
numevents = retval;
for (j = 0; j < numevents; j++) {
int mask = 0;
struct epoll_event *e = state->events+j;
if (e->events & EPOLLIN) mask |= AE_READABLE;
if (e->events & EPOLLOUT) mask |= AE_WRITABLE;
eventLoop->fired.fd = e->data.fd;
eventLoop->fired.mask = mask;
}
}
return numevents;
aeFiredEvent定义为：
/* A fired event */
typedef struct aeFiredEvent {
int fd;
int mask;
} aeFiredEvent;
回到aeProcessEvents函数，处理标记好的firedEvents：
for (j = 0; j < numevents; j++) {
aeFileEvent *fe = &eventLoop->events.fd];
int mask = eventLoop->fired.mask;
int fd = eventLoop->fired.fd;
int rfired = 0;
/* note the fe->mask & mask & ... code: maybe an already processed
* event removed an element that fired and we still didn't
* processed, so we check if the event is still valid. */
if (fe->mask & mask & AE_READABLE) {
rfired = 1;
fe->rfileProc(eventLoop,fd,fe->clientData,mask);
}
if (fe->mask & mask & AE_WRITABLE) {
if (!rfired || fe->wfileProc != fe->rfileProc)
fe->wfileProc(eventLoop,fd,fe->clientData,mask);
}
processed++;
}
aeFileEvent中定义了两种文件处理的回调函数：rfileProc和wfileProc，分别对应读写。
处理完文件事件之后，才处理时间事件：
/* Check time events */ if (flags & AE_TIME_EVENTS)
processed += processTimeEvents(eventLoop);其实现如下：
/* Process time events */
static int processTimeEvents(aeEventLoop *eventLoop) {
int processed = 0;
aeTimeEvent *te;
long long maxId;
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;
}
我们看到，也是通过调用aeTimeProc *类型的回调函数来处理事件。在遍历时间事件链表的过程中，对每个事件重复：如果事件已经处理完，retval的值标记为AE_NOMORE，则调用aeDeleteTimeEvent删除时间事件，否则，调用adAddMillisecondsToNow更新计时器。
最后返回已处理的事件数量：
return processed; /* return the number of processed file/time events */
作者：Aegeaner 发表于2012-2-27 15:12:49 原文链接
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