[libevent源码分析] event_add

event_add 把event往当前event中的ev_base追加,如果需要定时，那么tv不能为空

int
event_add(struct event *ev, const struct timeval *tv)
{
struct event_base *base = ev->ev_base;      //event_add 会把event加入到他的ev_base成员里
const struct eventop *evsel = base->evsel;  //对应linux的epoll相关函数
void *evbase = base->evbase;                //对应linux为 struct epollop
/*
* struct epollop
* {
*      struct evepoll *fds;                //分配nfiles个evepoll对象
*      int nfds;                           //支持的最大软限制数的句柄(上面的数组个数)
*      struct epoll_event* events;         //分配nfiles(软限制数) epoll_event对象
*      int nevents;                        //nevents保存着上面events个数
*      int epfd;                           //保存着epoll_create的句柄
* }
*/
int res = 0;

event_debug((
"event_add: event: %p, %s%s%scall %p",
ev,
ev->ev_events & EV_READ ? "EV_READ " : " ",
ev->ev_events & EV_WRITE ? "EV_WRITE " : " ",
tv ? "EV_TIMEOUT " : " ",
ev->ev_callback));

assert(!(ev->ev_flags & ~EVLIST_ALL));

if (tv != NULL && !(ev->ev_flags & EVLIST_TIMEOUT)) {
if (min_heap_reserve(&base->timeheap,
1 + min_heap_size(&base->timeheap)) == -1)
return (-1);  /* ENOMEM == errno */
}

if ((ev->ev_events & (EV_READ|EV_WRITE|EV_SIGNAL)) &&
!(ev->ev_flags & (EVLIST_INSERTED|EVLIST_ACTIVE))) {
res = evsel->add(evbase, ev);           //注册or修改事件到epoll中去
if (res != -1)
event_queue_insert(base, ev, EVLIST_INSERTED);  //把ev插入到eventqeue中去
}

/*
* 如果说插入事件成功同时设置了超时时间
*/
if (res != -1 && tv != NULL) {
struct timeval now;

/*
*如果已经存在了超时时间,那么就删除这个超时节点
*/
if (ev->ev_flags & EVLIST_TIMEOUT)
event_queue_remove(base, ev, EVLIST_TIMEOUT);

/* Check if it is active due to a timeout.  Rescheduling
* this timeout before the callback can be executed
* removes it from the active list. */
if ((ev->ev_flags & EVLIST_ACTIVE) &&
(ev->ev_res & EV_TIMEOUT)) {
/* See if we are just active executing this
* event in a loop
*/
if (ev->ev_ncalls && ev->ev_pncalls) {
/* Abort loop */
*ev->ev_pncalls = 0;
}

event_queue_remove(base, ev, EVLIST_ACTIVE);
}

gettime(base, &now);
evutil_timeradd(&now, tv, &ev->ev_timeout);

event_debug((
"event_add: timeout in %ld seconds, call %p",
tv->tv_sec, ev->ev_callback));

event_queue_insert(base, ev, EVLIST_TIMEOUT);//加入到最小超时堆中去
}

return (res);
}

如果新加的事件不为空，当前事件不是timeout时间，就为他在时间最小堆上分配一块可用空间(如果最小堆有空间，就不会重新分配)

关于最小堆可以连接我的githup,libevent用最小堆来管理定时事件，根节点永远是最小的而且算法时间最小

如果事件是EV_READ、EV_WRITE、EV_SIGNAL,并且事件不是插入or激活状态，那么就加入事件

以epoll为例

static int
epoll_add(void *arg, struct event *ev)
{
struct epollop *epollop = arg;
struct epoll_event epev = {0, {0}};
struct evepoll *evep;
int fd, op, events;

/*
* 信号的原理
* 1 设置信号处理函数，保存原来的信号处理函数到event的ev_base->sh_old中去
* 2 如果是首次添加信号，那么需要为所有信号追加一个信号事件来源自event->ev_base->ev_signal
*   同时设置event->ev_base->ev_signal->ev_signal_added,表示信号回调事件已经设置了
* 3 同时把事件追加到event->ev_base->ev_signal->evsigevents[signno]链表中去
*/
if (ev->ev_events & EV_SIGNAL)  //如果是加入的信号
return (evsignal_add(ev));

fd = ev->ev_fd;
if (fd >= epollop->nfds) {
/* Extent the file descriptor array as necessary */
//如果说当前的epoll中已经满足不了新加入的句柄
if (epoll_recalc(ev->ev_base, epollop, fd) == -1)
return (-1);
}

evep = &epollop->fds[fd];
op = EPOLL_CTL_ADD;
events = 0;
//如果事件之前是可读
if (evep->evread != NULL) {
events |= EPOLLIN;
op = EPOLL_CTL_MOD;
}
//如果事件之前是可写
if (evep->evwrite != NULL) {
events |= EPOLLOUT;
op = EPOLL_CTL_MOD;
}

//新加入事件设置的是可读事件
if (ev->ev_events & EV_READ)
events |= EPOLLIN;
//新加入事件设置的是可写事件
if (ev->ev_events & EV_WRITE)
events |= EPOLLOUT;

epev.data.ptr = evep;
epev.events = events;
if (epoll_ctl(epollop->epfd, op, ev->ev_fd, &epev) == -1)
return (-1);

/* Update events responsible */
if (ev->ev_events & EV_READ)
evep->evread = ev;
if (ev->ev_events & EV_WRITE)
evep->evwrite = ev;

return (0);
}

信号追加，libevent对信号采用sockpair 创建两个互连socket，信号激发写可写sock，可读加入到事件循环中去

根据信号ev_base->sig.evsigcaught[signumber]来判断该信号是否发生,下面是信号追加函数

int
evsignal_add(struct event *ev)
{
int evsignal;
struct event_base *base = ev->ev_base;          //信号event的base
struct evsignal_info *sig = &ev->ev_base->sig;  //信号在ev_base的管理结构

if (ev->ev_events & (EV_READ|EV_WRITE))         //信号事件不支持可读可写事件
event_errx(1, "%s: EV_SIGNAL incompatible use", __func__);
evsignal = EVENT_SIGNAL(ev);                    //信号的fd就是信号number
assert(evsignal >= 0 && evsignal < NSIG);       //信号不能超过NSIG这个数
if (TAILQ_EMPTY(&sig->evsigevents[evsignal])) { //如果说该信号链表为空
event_debug(("%s: %p: changing signal handler", __func__, ev));
//设置信号处理函数，同时，保存原来的信号处理函数到ev_base->sh_old中去
if (_evsignal_set_handler(
base, evsignal, evsignal_handler) == -1)
return (-1);

/* catch signals if they happen quickly */
evsignal_base = base;

if (!sig->ev_signal_added) {
if (event_add(&sig->ev_signal, NULL))
return (-1);
sig->ev_signal_added = 1;               //加入epoll_wait中去
}
}

//把ev->ev_signal_next加入到sig->evsigevents[evsignal]的链表末端
/* multiple events may listen to the same signal */
TAILQ_INSERT_TAIL(&sig->evsigevents[evsignal], ev, ev_signal_next);

return (0);
}

信号回调函数

/*
* 所有的信号都通用一个信号处理函数
*/
static void
evsignal_handler(int sig)
{
int save_errno = errno;     //保存错误码

if (evsignal_base == NULL) {
event_warn(
"%s: received signal %d, but have no base configured",
__func__, sig);
return;
}

evsignal_base->sig.evsigcaught[sig]++;  //引起的信号number++
evsignal_base->sig.evsignal_caught = 1; //设置信号标志，表示信号已经触发

#ifndef HAVE_SIGACTION
signal(sig, evsignal_handler);
#endif

/* Wake up our notification mechanism */
send(evsignal_base->sig.ev_signal_pair[0], "a", 1, 0);  //通过写sockpair写数据来触发epoll_wait返回
errno = save_errno;
}

定时事件采用最小堆，定时值+当前事件最为左后超时时间，加入到最小堆中去，主要在event_base_dispatch中使用

libeven 整个源码分析和sample都在我的 githup