libevent7
将event加入到队列后
调用
int
event_base_dispatch(struct event_base *event_base)
{
return (event_base_loop(event_base, 0));
}
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;
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);
}
/* 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);
调用复用IO的函数//该函数的内部会解锁，然后调用OS提供的的多路IO复用函数。
//这个函数退出后，又会立即加锁。这有点像条件变量。
res = evsel->dispatch(base, tv_p);
if (res == -1) {
event_debug(("%s: dispatch returned unsuccessfully.",
__func__));
retval = -1;
goto done;
}
update_time_cache(base);
timeout_process(base);
if (N_ACTIVE_CALLBACKS(base)) {
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);
}
static void
event_queue_make_later_events_active(struct event_base *base)
{
struct event_callback *evcb;
EVENT_BASE_ASSERT_LOCKED(base);
while ((evcb = TAILQ_FIRST(&base->active_later_queue))) {
TAILQ_REMOVE(&base->active_later_queue, evcb, evcb_active_next);
evcb->evcb_flags = (evcb->evcb_flags & ~EVLIST_ACTIVE_LATER) | EVLIST_ACTIVE;
EVUTIL_ASSERT(evcb->evcb_pri < base->nactivequeues);
TAILQ_INSERT_TAIL(&base->activequeues[evcb->evcb_pri], evcb, evcb_active_next);
base->n_deferreds_queued += (evcb->evcb_closure == EV_CLOSURE_CB_SELF);
}
}
上面代码中有两个函数evsel->dispatch和event_process_active。前一个将调用多路IO复用函数，对event进行监听，并且把满足条件的event放到event_base的激活队列中。后一个则遍历这个激活队列的所有event，逐个调用对应的回调函数。
以poll为例：
static int
poll_dispatch(struct event_base *base, struct timeval *tv)
{
int res, i, j, nfds;
long msec = -1;
struct pollop *pop = base->evbase;
struct pollfd *event_set;
poll_check_ok(pop);
nfds = pop->nfds;
#ifndef EVENT__DISABLE_THREAD_SUPPORT
if (base->th_base_lock) {
/* If we're using this backend in a multithreaded setting,
* then we need to work on a copy of event_set, so that we can
* let other threads modify the main event_set while we're
* polling. If we're not multithreaded, then we'll skip the
* copy step here to save memory and time. */
if (pop->realloc_copy) {
struct pollfd *tmp = mm_realloc(pop->event_set_copy,
pop->event_count * sizeof(struct pollfd));
if (tmp == NULL) {
event_warn("realloc");
return -1;
}
pop->event_set_copy = tmp;
pop->realloc_copy = 0;
}
memcpy(pop->event_set_copy, pop->event_set,
sizeof(struct pollfd)*nfds);
event_set = pop->event_set_copy;
} else {
event_set = pop->event_set;
}
#else
event_set = pop->event_set;
#endif
if (tv != NULL) {
msec = evutil_tv_to_msec_(tv);
if (msec < 0 || msec > INT_MAX)
msec = INT_MAX;
}
解锁
EVBASE_RELEASE_LOCK(base, th_base_lock);
res = poll(event_set, nfds, msec);
加锁
EVBASE_ACQUIRE_LOCK(base, th_base_lock);
if (res == -1) {
if (errno != EINTR) {
event_warn("poll");
return (-1);
}
return (0);
}
event_debug(("%s: poll reports %d", __func__, res));
if (res == 0 || nfds == 0)
return (0);
i = evutil_weakrand_range_(&base->weakrand_seed, nfds);
for (j = 0; j < nfds; j++) {
int what;
if (++i == nfds)
i = 0;
what = event_set[i].revents;
if (!what)
continue;
res = 0;
//如果fd发生错误，就把之当作读和写事件。之后调用read
//或者write时，就能得知具体是什么错误了。这里的作用是
//通知到上层。
/* If the file gets closed notify */
if (what & (POLLHUP|POLLERR))
what |= POLLIN|POLLOUT;
if (what & POLLIN)
res |= EV_READ;
if (what & POLLOUT)
res |= EV_WRITE;
if (res == 0)
continue;
加入到激活队列
evmap_io_active_(base, event_set[i].fd, res);
}
return (0);
}
pollfd数组的数据是在evmap_io_add函数中添加的，在evmap_io_add函数里面， 有一个evsel->add调用，它会把数据(fd和对应的监听类型)放到pollfd数组中。
void
evmap_io_active_(struct event_base *base, evutil_socket_t fd, short events)
{
struct event_io_map *io = &base->io;
struct evmap_io *ctx;
struct event *ev;
#ifndef EVMAP_USE_HT
if (fd < 0 || fd >= io->nentries)
return;
#endif
GET_IO_SLOT(ctx, io, fd, evmap_io); //由这个fd找到对应event_map_entry的TAILQ_HEAD.
if (NULL == ctx)
return;
LIST_FOREACH(ev, &ctx->events, ev_io_next) {//遍历这个队列。将所有与fd相关联的event结构体都处理一遍
if (ev->ev_events & events)
event_active_nolock_(ev, ev->ev_events & events, 1);
}
void
event_active_nolock_(struct event *ev, int res, short ncalls)
{
struct event_base *base;
event_debug(("event_active: %p (fd "EV_SOCK_FMT"), res %d, callback %p",
ev, EV_SOCK_ARG(ev->ev_fd), (int)res, ev->ev_callback));
base = ev->ev_base;
EVENT_BASE_ASSERT_LOCKED(base);
if (ev->ev_flags & EVLIST_FINALIZING) {
/* XXXX debug */
return;
}
switch ((ev->ev_flags & (EVLIST_ACTIVE|EVLIST_ACTIVE_LATER))) {
default:
case EVLIST_ACTIVE|EVLIST_ACTIVE_LATER:
EVUTIL_ASSERT(0);
break;
case EVLIST_ACTIVE:
/* We get different kinds of events, add them together */
ev->ev_res |= res;
return;
case EVLIST_ACTIVE_LATER:
ev->ev_res |= res;
break;
case 0:
ev->ev_res = res;
break;
}
if (ev->ev_pri < base->event_running_priority)
base->event_continue = 1;
if (ev->ev_events & EV_SIGNAL) {
#ifndef EVENT__DISABLE_THREAD_SUPPORT
if (base->current_event == event_to_event_callback(ev) &&
!EVBASE_IN_THREAD(base)) {
++base->current_event_waiters;
EVTHREAD_COND_WAIT(base->current_event_cond, base->th_base_lock);
}
#endif
ev->ev_ncalls = ncalls;
ev->ev_pncalls = NULL;
}
event_callback_activate_nolock_(base, event_to_event_callback(ev));
}
int
event_callback_activate_nolock_(struct event_base *base,
struct event_callback *evcb)
{
int r = 1;
if (evcb->evcb_flags & EVLIST_FINALIZING)
return 0;
switch (evcb->evcb_flags & (EVLIST_ACTIVE|EVLIST_ACTIVE_LATER)) {
default:
EVUTIL_ASSERT(0);
case EVLIST_ACTIVE_LATER:
event_queue_remove_active_later(base, evcb);
r = 0;
break;
case EVLIST_ACTIVE:
return 0;
case 0:
break;
}
event_queue_insert_active(base, evcb); 插入激活队列
if (EVBASE_NEED_NOTIFY(base)) 不是主线程 是次线程 就通知主线程
evthread_notify_base(base);
return r;
}
处理函数
/*
* Active events are stored in priority queues. Lower priorities are always
* process before higher priorities. Low priority events can starve high
* priority ones.
*/
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;
}
//从高优先级到低优先级遍历优先级数组
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)
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;
}
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);处理回调函数
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);回调函数
}
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;
}
上面的代码，从高到低优先级遍历激活event优先级数组。对于激活的event，要调用event_queue_remove将之从激活队列中删除掉。然后再对这个event调用其回调函数。
event_queue_remove函数的调用会改变event结构体的ev_flags变量的值。调用后， ev_flags变量为EVLIST_INIT | EVLIST_INSERTED。现在又可以等待下一次事件的到来了
struct event_callback ev_evcallback;
/* for managing timeouts */
union {
TAILQ_ENTRY(event) ev_next_with_common_timeout;
int min_heap_idx; //指明该event结构体在堆的位置
} ev_timeout_pos; //仅用于定时事件处理器(event).EV_TIMEOUT类型
//对于I/O事件，是文件描述符；对于signal事件，是信号值
evutil_socket_t ev_fd;
struct event_base *ev_base; //所属的event_base
//因为信号和I/O是不能同时设置的。所以可以使用共用体以省内存
//在低版本的Libevent，两者是分开的，不在共用体内。
union {
//无论是信号还是IO，都有一个TAILQ_ENTRY的队列。它用于这样的情景:
//用户对同一个fd调用event_new多次，并且都使用了不同的回调函数。
//每次调用event_new都会产生一个event*。这个xxx_next成员就是把这些
//event连接起来的。
/* used for io events */
//用于IO事件
struct {
TAILQ_ENTRY(event) ev_io_next;
struct timeval ev_timeout;
} ev_io;
/* used by signal events */
//用于信号事件
struct {
TAILQ_ENTRY(event) ev_signal_next;
short ev_ncalls; //事件就绪执行时，调用ev_callback的次数 /* Allows deletes in callback */
short *ev_pncalls; //指针，指向次数
} ev_signal;
} _ev;
short ev_events;//记录监听的事件类型 EV_READ EVTIMEOUT之类
short ev_res; /* result passed to event callback *///记录了当前激活事件的类型
//libevent用于标记event信息的字段，表明其当前的状态.
//可能值为前面的EVLIST_XXX
short ev_flags;
struct timeval ev_timeout;//用于定时器,指定定时器的超时值
/* allows us to adopt for different types of events */
void (*ev_callback)(evutil_socket_t, short, void *arg); //回调函数
void *ev_arg; //回调函数的参数
};
TAILQ_ENTRY(event_callback) evcb_active_next;
//本event的优先级。调用event_priority_set设置
ev_uint8_t evcb_pri; /* smaller numbers are higher priority */
ev_uint8_t evcb_closure;
/* allows us to adopt for different types of events */
union {
void (*evcb_callback)(evutil_socket_t, short, void *);
void (*evcb_selfcb)(struct event_callback *, void *);
void (*evcb_evfinalize)(struct event *, void *);
void (*evcb_cbfinalize)(struct event_callback *, void *);
} evcb_cb_union;
void *evcb_arg;
};
#define ev_pri ev_evcallback.evcb_pri
#define ev_flags ev_evcallback.evcb_flags
#define ev_closure ev_evcallback.evcb_closure
#define ev_callback ev_evcallback.evcb_cb_union.evcb_callback
#define ev_arg ev_evcallback.evcb_arg
优先级设置
int
event_base_priority_init(struct event_base *base, int npriorities)
{
int i, r;
r = -1;
EVBASE_ACQUIRE_LOCK(base, th_base_lock);
//由N_ACTIVE_CALLBACKS宏可以知道，本函数应该要在event_base_dispatch
//函数调用前调用。不然将无法设置。
if (N_ACTIVE_CALLBACKS(base) || npriorities < 1
|| npriorities >= EVENT_MAX_PRIORITIES)
goto err;
if (npriorities == base->nactivequeues)/之前和现在要设置的优先级数是一样的。
goto ok;
if (base->nactivequeues) {
mm_free(base->activequeues);
base->nactivequeues = 0;
}
/* Allocate our priority queues */ //分配一个优先级数组。
base->activequeues = (struct evcallback_list *)
mm_calloc(npriorities, sizeof(struct evcallback_list));
if (base->activequeues == NULL) {
event_warn("%s: calloc", __func__);
goto err;
}
base->nactivequeues = npriorities;
for (i = 0; i < base->nactivequeues; ++i) {
TAILQ_INIT(&base->activequeues[i]);
}
ok:
r = 0;
err:
EVBASE_RELEASE_LOCK(base, th_base_lock);
return (r);
}
int
event_priority_set(struct event *ev, int pri)
{
event_debug_assert_is_setup_(ev);
if (ev->ev_flags & EVLIST_ACTIVE)
return (-1);
if (pri < 0 || pri >= ev->ev_base->nactivequeues)//优先级不能越界
return (-1);
#define ev_pri ev_evcallback.evcb_pri
ev->ev_pri = pri; 新的版本有个宏替换 //pri值越小，其优先级就越高。
return (0);
}
在
event_callback_activate_nolock_(struct event_base *base,
struct event_callback *evcb)
中会调用evthread_notify_base
struct event_base {…
//event_base是否处于通知的未决状态。即次线程已经通知了，但主线程还没处理这个通知
int is_notify_pending;
evutil_socket_t th_notify_fd[2]; //通信管道
struct event th_notify;//用于监听th_notify_fd的读端
//有两个可供选择的通知函数，指向其中一个通知函数
int (*th_notify_fn)(struct event_base *base);
};
/** Tell the thread currently running the event_loop for base (if any) that it
* needs to stop waiting in its dispatch function (if it is) and process all
* active callbacks. */
static int
evthread_notify_base(struct event_base *base)
{
EVENT_BASE_ASSERT_LOCKED(base);加锁
if (!base->th_notify_fn)
return -1;
if (base->is_notify_pending) //写入一个字节，就能使event_base被唤醒。
//如果处于未决状态，就没必要写多一个字节
return 0;
base->is_notify_pending = 1;
return base->th_notify_fn(base);
}
在event_base_new_with_config(event_base_new会调用该函数)里面会调用evthread_make_base_notifiable函数，其中会设置
th_notify_fn函数指针；这里以evthread_notify_base_default作为默认值。这个evthread_notify_base_default完成实际的通知操作
同时也会设置回调函数；
/* Helper callback: wake an event_base from another thread. This version
* works by writing a byte to one end of a socketpair, so that the event_base
* listening on the other end will wake up as the corresponding event
* triggers */
static int
evthread_notify_base_default(struct event_base *base)
{
char buf[1];
int r;
buf[0] = (char) 0;
#ifdef _WIN32 //通知一下，用来唤醒。写一个字节足矣
r = send(base->th_notify_fd[1], buf, 1, 0);
#else
r = write(base->th_notify_fd[1], buf, 1);
#endif return (r < 0 && ! EVUTIL_ERR_IS_EAGAIN(errno)) ? -1 : 0; //即使errno 等于 EAGAIN也无所谓，因为这是由于通信通道已经塞满了
//这已经能唤醒主线程了。没必要一定要再写入一个字节
}
只是往管道里面写入一个字节。当然这已经能使得event_base检测到管道可读，从而实现唤醒event_base。
往管道写入一个字节，event_base就会被唤醒，然后调用这个管道对应event的回调函数。当然，在event_base醒来的时候，还能看到其他东西。这也是Libevent提供唤醒功能的原因。
回调函数static void
evthread_notify_drain_default(evutil_socket_t fd, short what, void *arg)
{
unsigned char buf[1024];
struct event_base *base = arg;
#ifdef _WIN32
while (recv(fd, (char*)buf, sizeof(buf), 0) > 0)
;
#else
while (read(fd, (char*)buf, sizeof(buf)) > 0)
;
#endif
EVBASE_ACQUIRE_LOCK(base, th_base_lock);
base->is_notify_pending = 0; //修改之，使得其不再是未决的了。当然这也能让其他线程可以再次唤醒值。参看evthread_notify_base函数
EVBASE_RELEASE_LOCK(base, th_base_lock);
}