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watcher的核心业务函数watch：
（1）如果count为0，没有要监听的句柄，则watcher状态设置为WATCHER_STOPPED，返回，返回值为JOB_REQUEUE_NONE，这会返回到“【11】Strongswan processor 详解1”中的process_job返回处，销毁watcher job。再调用add时，再加入。
（2）watcher状态机WATCHER_QUEUED-》 WATCHER_RUNNING；
（3）使用poll机制，

struct pollfd {int fd; // 文件描述符short events; // 需要监控的事件short revents; // 实际发生的事件
};//根据监听的fd数量分配pollfd空间，此外为pipe管道的读事件也额外分配一个pfd空间。
pfd = alloca(sizeof(*pfd) * (count + 1));
//监听pipe管道的读事件
pfd[0].fd = this->notify[0];
pfd[0].events = POLLIN;//遍历pipe管道的读事件之外的所有监听fd，设置pfd
count = 1;
for (entry = this->fds; entry; entry = entry->next)
{//in_callback在notify中++，在notify_end中--，作用是已有事件没处理完（异步地processor那里没有处理完）先不再加入pfd监测，if (!entry->in_callback){pfd[count].fd = entry->fd;pfd[count].events = 0;reset_event_log(eventbuf, eventpos);if (entry->events & WATCHER_READ){log_event(eventpos, 'r');pfd[count].events |= POLLIN;}if (entry->events & WATCHER_WRITE){log_event(eventpos, 'w');pfd[count].events |= POLLOUT;}end_event_log(eventpos);log_fd(logpos, loglen, entry->fd, eventbuf);count++;}
}

(4) 调用poll

thread_cleanup_push((void*)activate_all, this);
old = thread_cancelability(TRUE);res = poll(pfd, count, -1);
if (res == -1 && errno == EINTR)
{/* LinuxThreads interrupts poll(), but does not make it a* cancellation point. Manually test if we got canceled. */thread_cancellation_point();
}thread_cancelability(old);
//参数false，压入的activate_all不执行
thread_cleanup_pop(FALSE);......
//revents 为实际发生的事件，没有发生则为空
if (pfd[0].revents & POLLIN)
{while (TRUE){//pipe O_NONBLOCK enable：当当没有数据可读时，调用返回-1，errno值为EAGAIN，跳出循环//有数据时，读到buf中， len = read(this->notify[0], buf, sizeof(buf));if (len == -1){if (errno != EAGAIN && errno != EWOULDBLOCK){DBG1(DBG_JOB, "reading watcher notify failed: %s",strerror(errno));}break;}}this->pending = FALSE;DBG2(DBG_JOB, "watcher got notification, rebuilding");break;
}......
for (entry = this->fds; entry; entry = entry->next)
{//?if (entry->in_callback){continue;}reset_event_log(eventbuf, eventpos);//返回当前entry->fd对应pfd的实际发生事件，可能为空没发生或发生，也可能是错误revents = find_revents(pfd, count, entry->fd);if (revents & POLLERR){log_event(eventpos, 'e');}if (revents & POLLIN){log_event(eventpos, 'r');}if (revents & POLLOUT){log_event(eventpos, 'w');}//fd的读事件，如socket收到了数据if (entry->events & WATCHER_READ &&revents & (POLLIN | POLLERR | POLLHUP | POLLNVAL)){//notify暂时将entry插入jobs队列，后续统一在（5）中再加入processor的job队列处理notify(this, entry, WATCHER_READ);}//fd的写事件，如socket发送数据if (entry->events & WATCHER_WRITE &&revents & (POLLOUT | POLLERR | POLLHUP | POLLNVAL)){notify(this, entry, WATCHER_WRITE);}end_event_log(eventpos);log_fd(logpos, loglen, entry->fd, eventbuf);
}

notify函数：

/*** 为已注册的 FD 执行回调*/
static void notify(private_watcher_t *this, entry_t *entry,watcher_event_t event)
{notify_data_t *data;/* 获取 Async Job 的 entry 副本，但具有特定事件 */INIT(data,.entry = entry,.fd = entry->fd,.event = event,.cb = entry->cb,.data = entry->data,.keep = TRUE,.this = this,);/* deactivate entry，这样我们就可以 poll（） 其他 FDs，即使异步处理还没有处理该事件 *///换句话说，processer异步处理完成该事件，再重新poll该事件entry->in_callback++;//notify_async是该事件业务的最终调用，会调用该事件的处理回调this->jobs->insert_last(this->jobs,callback_job_create_with_prio((void*)notify_async, data,(void*)notify_end, (callback_job_cancel_t)return_false,JOB_PRIO_CRITICAL));
}/*** 执行已注册 FD 的回调，异步*/
static job_requeue_t notify_async(notify_data_t *data)
{thread_cleanup_push((void*)unregister, data);data->keep = data->cb(data->data, data->fd, data->event);thread_cleanup_pop(FALSE);//只执行一次，在processor的process_job中销毁该事件对应processor里的job时会调用notify_end，见（6）return JOB_REQUEUE_NONE;
}

（5）watcher 监听fd有事件时，

if (this->jobs->get_count(this->jobs))
{while (this->jobs->remove_first(this->jobs,(void**)&job) == SUCCESS){lib->processor->execute_job(lib->processor, job);}/* we temporarily disable a notified FD, rebuild FDSET */break;
}

（6）notify_end

/*** 清理通知数据，重新激活 FD*/
static void notify_end(notify_data_t *data)
{private_watcher_t *this = data->this;entry_t *entry, *prev = NULL;watcher_event_t updated = 0;bool removed = FALSE;/* reactivate the disabled entry */this->mutex->lock(this->mutex);//遍历watcher的fds，匹配后，判断该事件业务函数的返回值（见notify_async的data->keep = data->cb(data->data, data->fd, data->event);）如果不保持则从fds中移除该事件，注意in_callback--，以便于该事件可以重新pollfor (entry = this->fds; entry; prev = entry, entry = entry->next){if (entry == data->entry){if (!data->keep){//可能的读写事件互换，这发生事件业务回调里面修改了data->event（见notify_async中的data->cb）entry->events &= ~data->event;updated = entry->events;if (!entry->events){remove_entry(this, entry, prev);removed = TRUE;break;}}entry->in_callback--;break;}}this->condvar->broadcast(this->condvar);update_and_unlock(this);if (removed){DBG3(DBG_JOB, "removed fd %d[%s%s] from watcher after callback", data->fd,data->event & WATCHER_READ ? "r" : "",data->event & WATCHER_WRITE ? "w" : "");}else if (updated){DBG3(DBG_JOB, "updated fd %d[%s%s] to %d[%s%s] after callback", data->fd,(updated | data->event) & WATCHER_READ ? "r" : "",(updated | data->event) & WATCHER_WRITE ? "w" : "", data->fd,updated & WATCHER_READ ? "r" : "",updated & WATCHER_WRITE ? "w" : "");}free(data);
}