libevent（2）
event_set（）函数：在将事件注册事件处理框架之前，应该先调用event_set对事件进行相关设置。
int
event_assign(struct event *ev, struct event_base *base, evutil_socket_t fd, short events, void (*callback)(evutil_socket_t, short, void *), void *arg)
{
if (!base)
base = current_base;
if (arg == &event_self_cbarg_ptr_)
arg = ev;
event_debug_assert_not_added_(ev);
ev->ev_base = base;
ev->ev_callback = callback;
ev->ev_arg = arg;
ev->ev_fd = fd;
ev->ev_events = events;
ev->ev_res = 0;
ev->ev_flags = EVLIST_INIT;
ev->ev_ncalls = 0;
ev->ev_pncalls = NULL;
if (events & EV_SIGNAL) {
if ((events & (EV_READ|EV_WRITE|EV_CLOSED)) != 0) {
event_warnx("%s: EV_SIGNAL is not compatible with "
"EV_READ, EV_WRITE or EV_CLOSED", __func__);
return -1;
}
ev->ev_closure = EV_CLOSURE_EVENT_SIGNAL;
} else {
if (events & EV_PERSIST) {
evutil_timerclear(&ev->ev_io_timeout);
ev->ev_closure = EV_CLOSURE_EVENT_PERSIST;
} else {
ev->ev_closure = EV_CLOSURE_EVENT;
}
}
min_heap_elem_init_(ev);
if (base != NULL) {
/* by default, we put new events into the middle priority */
ev->ev_pri = base->nactivequeues / 2;
}
event_debug_note_setup_(ev);
return 0;
/*设置event对象**ev:事件对象
**fd:事件对应的文件描述符或信号,对于定时器设为-1
**events:事件类型，比如 EV_READ,EV_PERSIST, EV_WRITE, EV_SIGNAL
**callback:事件的回调函数
**arg:回调函数参数
*/
event_set(struct event *ev, evutil_socket_t fd, short events,
void (*callback)(evutil_socket_t, short, void *), void *arg)
{
int r;
r = event_assign(ev, current_base, fd, events, callback, arg);
EVUTIL_ASSERT(r == 0);
}
对于I/O事件，通过event_add将其加入event_base的注册事件链表eventqueue ；就绪时会加入event_base的就绪链表activequeues[]；
对于timer事件，event_add将其加入到event_base的小根堆timeheap；
Signale事件的管理相对复杂些，event_add将其加入到注册事件链表，同时，event_add内部会调用I/O demultiplex的add函数（对于I/O事件也一样），比如epoll_add。而add函数又会调用evsignal_add将其加入到evsignal_info的evsigevents[signo]链表(关于signal，后面会详细介绍)。
事件处理框架主循环
Libevent将I/O事件、signal事件和timer事件用统一的模型进行处理，这是非常精妙的。libevent主循环函数不断检测注册事件，如果有事件发生，则将其放入就绪链表，并调用事件的回调函数，完成业务逻辑处理。
//事件处理主循环
int
event_dispatch(void)
这是呈现给外部的接口，它的实现很简单，即调用event_loop，而event_loop调用event_base_loop，event_base_loop完成实际的主循环逻辑。
int
event_dispatch(void)
这是呈现给外部的接口，它的实现很简单，即调用event_loop，而event_loop调用event_base_loop，event_base_loop完成实际的主循环逻辑。
int
event_base_loop(struct event_base *base, int flags)
{
const struct eventop *evsel = base->evsel;
struct timeval tv;
struct timeval *tv_p;
int res, done, retval = 0;
/* Grab the lock. We will release it inside evsel.dispatch, and again
* as we invoke user callbacks. */
EVBASE_ACQUIRE_LOCK(base, th_base_lock);
if (base->running_loop) {
event_warnx("%s: reentrant invocation. Only one event_base_loop"
" can run on each event_base at once.", __func__);
EVBASE_RELEASE_LOCK(base, th_base_lock);
return -1;
}
base->running_loop = 1;
clear_time_cache(base);
if (base->sig.ev_signal_added && base->sig.ev_n_signals_added)
evsig_set_base_(base);
done = 0;
#ifndef EVENT__DISABLE_THREAD_SUPPORT
base->th_owner_id = EVTHREAD_GET_ID();
#endif
base->event_gotterm = base->event_break = 0;
while (!done) {
base->event_continue = 0;
base->n_deferreds_queued = 0;
/* Terminate the loop if we have been asked to */
if (base->event_gotterm) {
break;
}
if (base->event_break) {
break;
}
tv_p = &tv;
/* 如果没有就绪事件，根据timer heap中事件的最小超时间，计算I/O demultipex的
****最大等待时间，相反如果有就绪事件，则清除tv，即I/Odemultipex不应该等待
*/
if (!N_ACTIVE_CALLBACKS(base) && !(flags & EVLOOP_NONBLOCK)) {
timeout_next(base, &tv_p);
} else {
/*
* if we have active events, we just poll new events
* without waiting.
*/
evutil_timerclear(&tv);
}
/* 如果没有事件，则退出循环*/
/* If we have no events, we just exit */
if (0==(flags&EVLOOP_NO_EXIT_ON_EMPTY) &&
!event_haveevents(base) && !N_ACTIVE_CALLBACKS(base)) {
event_debug(("%s: no events registered.", __func__));
retval = 1;
goto done;
}
event_queue_make_later_events_active(base);
clear_time_cache(base);
/* tv_p 为I/O demultipex 的超时时间
*** 处理信号signal 事件和I/O事件
*/
res = evsel->dispatch(base, tv_p);
if (res == -1) {
event_debug(("%s: dispatch returned unsuccessfully.",
__func__));
retval = -1;
goto done;
}
update_time_cache(base);
// 处理timeout事件,对于超时的事件,将其放到就绪事件链表
timeout_process(base);
if (N_ACTIVE_CALLBACKS(base)) {<span style="font-family: Arial, Helvetica, sans-serif;"> //处理就绪事件</span>
int n = event_process_active(base);
if ((flags & EVLOOP_ONCE)
&& N_ACTIVE_CALLBACKS(base) == 0
&& n != 0)
done = 1;
} else if (flags & EVLOOP_NONBLOCK)
done = 1;
}
event_debug(("%s: asked to terminate loop.", __func__));
done:
clear_time_cache(base);
base->running_loop = 0;
EVBASE_RELEASE_LOCK(base, th_base_lock);
return (retval);
}
/* not thread safe */
int
event_loop(int flags)
{
return event_base_loop(current_base, flags);
}
int
event_dispatch(void)
{
return (event_loop(0));
}
timeout_next:
根据timer heap中事件的最小超时时间，计算I/Odemultipex的最大等待时间。
为了及时处理timer事件；I/O demultipex的最大等待时间应该不超过timer事件中最小的超时时间；否则，timer事件就不能得到及时的处理
static int
timeout_next(struct event_base *base, struct timeval **tv_p)
{
/* Caller must hold th_base_lock */
struct timeval now;
struct event *ev;
struct timeval *tv = *tv_p;
int res = 0;
//如果没有timer事件,则直接返回</span>
ev = min_heap_top_(&base->timeheap);
if (ev == NULL) {
/* if no time-based events are active wait for I/O */
*tv_p = NULL;
goto out;
}
if (gettime(base, &now) == -1) {
res = -1;
goto out;
}
//如果最小的timer事件已经超时,则清除tv,即I/O demultiplex不应该等待.
if (evutil_timercmp(&ev->ev_timeout, &now, <=)) {
evutil_timerclear(tv);
goto out;
}
更新I/O demultiplex可以等待的最大时间:ev->ev_timeout - now
evutil_timersub(&ev->ev_timeout, &now, tv);
EVUTIL_ASSERT(tv->tv_sec >= 0);
EVUTIL_ASSERT(tv->tv_usec >= 0);
event_debug(("timeout_next: event: %p, in %d seconds, %d useconds", ev, (int)tv->tv_sec, (int)tv->tv_usec));
out:
return (res);
}
3.4 dispatch函数
调用底层I/O multiplex的dispatch函数，具体的实现可以参见epoll的实现epoll_dispatch。
event_process_active函数的处理
/*
Helper for event_process_active to process all the events in a single queue,
releasing the lock as we go. This function requires that the lock be held
when it's invoked. Returns -1 if we get a signal or an event_break that
means we should stop processing any active events now. Otherwise returns
the number of non-internal event_callbacks that we processed.
*/
static int
event_process_active_single_queue(struct event_base *base,
struct evcallback_list *activeq,
int max_to_process, const struct timeval *endtime)
{
struct event_callback *evcb;
int count = 0;
EVUTIL_ASSERT(activeq != NULL);
for (evcb = TAILQ_FIRST(activeq); evcb; evcb = TAILQ_FIRST(activeq)) {
struct event *ev=NULL;
if (evcb->evcb_flags & EVLIST_INIT) {
ev = event_callback_to_event(evcb);
if (ev->ev_events & EV_PERSIST || ev->ev_flags & EVLIST_FINALIZING)
event_queue_remove_active(base, evcb);
else
event_del_nolock_(ev, EVENT_DEL_NOBLOCK);
event_debug((
"event_process_active: event: %p, %s%s%scall %p",
ev,
ev->ev_res & EV_READ ? "EV_READ " : " ",
ev->ev_res & EV_WRITE ? "EV_WRITE " : " ",
ev->ev_res & EV_CLOSED ? "EV_CLOSED " : " ",
ev->ev_callback));
} else {
event_queue_remove_active(base, evcb);
event_debug(("event_process_active: event_callback %p, "
"closure %d, call %p",
evcb, evcb->evcb_closure, evcb->evcb_cb_union.evcb_callback));
}
if (!(evcb->evcb_flags & EVLIST_INTERNAL))
++count;
base->current_event = evcb;
#ifndef EVENT__DISABLE_THREAD_SUPPORT
base->current_event_waiters = 0;
#endif
switch (evcb->evcb_closure) {
case EV_CLOSURE_EVENT_SIGNAL:
EVUTIL_ASSERT(ev != NULL);
event_signal_closure(base, ev);
break;
case EV_CLOSURE_EVENT_PERSIST:
EVUTIL_ASSERT(ev != NULL);
event_persist_closure(base, ev);
break;
case EV_CLOSURE_EVENT: {
void (*evcb_callback)(evutil_socket_t, short, void *);
EVUTIL_ASSERT(ev != NULL);
evcb_callback = *ev->ev_callback;
EVBASE_RELEASE_LOCK(base, th_base_lock);
evcb_callback(ev->ev_fd, ev->ev_res, ev->ev_arg);
}
break;
case EV_CLOSURE_CB_SELF: {
void (*evcb_selfcb)(struct event_callback *, void *) = evcb->evcb_cb_union.evcb_selfcb;
EVBASE_RELEASE_LOCK(base, th_base_lock);
evcb_selfcb(evcb, evcb->evcb_arg);
}
break;
case EV_CLOSURE_EVENT_FINALIZE:
case EV_CLOSURE_EVENT_FINALIZE_FREE: {
void (*evcb_evfinalize)(struct event *, void *);
int evcb_closure = evcb->evcb_closure;
EVUTIL_ASSERT(ev != NULL);
base->current_event = NULL;
evcb_evfinalize = ev->ev_evcallback.evcb_cb_union.evcb_evfinalize;
EVUTIL_ASSERT((evcb->evcb_flags & EVLIST_FINALIZING));
EVBASE_RELEASE_LOCK(base, th_base_lock);
evcb_evfinalize(ev, ev->ev_arg);
event_debug_note_teardown_(ev);
if (evcb_closure == EV_CLOSURE_EVENT_FINALIZE_FREE)
mm_free(ev);
}
break;
case EV_CLOSURE_CB_FINALIZE: {
void (*evcb_cbfinalize)(struct event_callback *, void *) = evcb->evcb_cb_union.evcb_cbfinalize;
base->current_event = NULL;
EVUTIL_ASSERT((evcb->evcb_flags & EVLIST_FINALIZING));
EVBASE_RELEASE_LOCK(base, th_base_lock);
evcb_cbfinalize(evcb, evcb->evcb_arg);
}
break;
default:
EVUTIL_ASSERT(0);
}
EVBASE_ACQUIRE_LOCK(base, th_base_lock);
base->current_event = NULL;
#ifndef EVENT__DISABLE_THREAD_SUPPORT
if (base->current_event_waiters) {
base->current_event_waiters = 0;
EVTHREAD_COND_BROADCAST(base->current_event_cond);
}
#endif
if (base->event_break)
return -1;
if (count >= max_to_process)
return count;
if (count && endtime) {
struct timeval now;
update_time_cache(base);
gettime(base, &now);
if (evutil_timercmp(&now, endtime, >=))
return count;
}
if (base->event_continue)
break;
}
return count;
}
/* * Active events are stored in priority queues. Lower priorities are always * process before higher priorities. Low priority events can starve high * priority ones.
*/
// 处理事件位于优先队列中，低优先级的通常比高优先级的先处理 有可能高优先级的队列会饿死
static int
event_process_active(struct event_base *base)
{
/* Caller must hold th_base_lock */
struct evcallback_list *activeq = NULL;
int i, c = 0;
const struct timeval *endtime;
struct timeval tv;
const int maxcb = base->max_dispatch_callbacks;
const int limit_after_prio = base->limit_callbacks_after_prio;
if (base->max_dispatch_time.tv_sec >= 0) {
update_time_cache(base);
gettime(base, &tv);
evutil_timeradd(&base->max_dispatch_time, &tv, &tv);
endtime = &tv;
} else {
endtime = NULL;
}
for (i = 0; i < base->nactivequeues; ++i) {
if (TAILQ_FIRST(&base->activequeues[i]) != NULL) {
base->event_running_priority = i;
activeq = &base->activequeues[i];
if (i < limit_after_prio)
//调用事件处理函数
c = event_process_active_single_queue(base, activeq,
INT_MAX, NULL);
else
c = event_process_active_single_queue(base, activeq,
maxcb, endtime);
if (c < 0) {
goto done;
} else if (c > 0)
break; /* Processed a real event; do not
* consider lower-priority events */
/* If we get here, all of the events we processed
* were internal. Continue. */
}
}
done:
base->event_running_priority = -1;
return c;
}