libevent源代码分析——event_dispatch() (二)

在上篇文章中介绍关于event_dispatch的大体框架，这里对其中的几个重要的函数解释说明

1、timeout_correct(base,&tv)

static void 889 timeout_correct(struct event_base *base, struct timeval *tv) 890 { 891     struct event **pev; 892     unsigned int size; 893     struct timeval off; 894  895     if (use_monotonic) 896         return; 897  898     /* Check if time is running backwards */ 899     gettime(base, tv); 900     if (evutil_timercmp(tv, &base->event_tv, >=)) { 901         base->event_tv = *tv; 902         return; 903     } 904  905     event_debug(("%s: time is running backwards, corrected", 906             __func__)); 907     evutil_timersub(&base->event_tv, tv, &off); 908  909     /* 910      * We can modify the key element of the node without destroying 911      * the key, beause we apply it to all in the right order. 912      */ 913     pev = base->timeheap.p; 914     size = base->timeheap.n; 915     for (; size-- > 0; ++pev) { 916         struct timeval *ev_tv = &(**pev).ev_timeout; 917         evutil_timersub(ev_tv, &off, ev_tv); 918     } 919     /* Now remember what the new time turned out to be. */ 920     base->event_tv = *tv; 921 }

这个函数的功能就是获取系统时间，在这个函数中调用的就是gettime()，在这个函数如果发现存放时间的缓冲区没有被清空，那么就使用当前保存的时间直接返回，如果缓冲区没有时间可以被利用，那么只能调用系统调用来获取时间，在上篇文章已经看到，很显然在event_base_loop中的第482行已经将时间缓冲区清空了,所以在这里使用gettime是不会在头两行就返回的。好像这里900行左右的代码是没有什么作用的，907行的比较函数时间值的大小。514行的判断：如果当前的激活事件为0，也就是没有什么激活事件，那么就提取一个时间，这个时间是将来要循环的最大时间。

static void 365 event_process_active(struct event_base *base) 366 { 367     struct event *ev; 368     struct event_list *activeq = NULL; 369     int i; 370     short ncalls; 371  372     for (i = 0; i < base->nactivequeues; ++i) { 373         if (TAILQ_FIRST(base->activequeues[i]) != NULL) { 374             activeq = base->activequeues[i]; 375             break; 376         } 377     } 378  379     assert(activeq != NULL); 380  381     for (ev = TAILQ_FIRST(activeq); ev; ev = TAILQ_FIRST(activeq)) { 382         if (ev->ev_events & EV_static void 365 event_process_active(struct event_base *base) 366 { 367     struct event *ev; 368     struct event_list *activeq = NULL; 369     int i; 370     short ncalls; 371  372     for (i = 0; i < base->nactivequeues; ++i) { 373         if (TAILQ_FIRST(base->activequeues[i]) != NULL) { 374             activeq = base->activequeues[i]; 375             break; 376         } 377     } 378  379     assert(activeq != NULL); 380  381     for (ev = TAILQ_FIRST(activeq); ev; ev = TAILQ_FIRST(activeq)) { 382         if (ev->ev_events & EV_PERSIST) 383             event_queue_remove(base, ev, EVLIST_ACTIVE); 384         else 385             event_del(ev); 386  387         /* Allows deletes to work */ 388         ncalls = ev->ev_ncalls; 389         ev->ev_pncalls = &ncalls; 390         while (ncalls) { 391             ncalls--; 392             ev->ev_ncalls = ncalls; 393             (*ev->ev_callback)((int)ev->ev_fd, ev->ev_res, ev->ev_arg); 394             if (event_gotsig || base->event_break) 395                 return; 396         } 397     } 398 }) 383             event_queue_remove(base, ev, EVLIST_ACTIVE); 384         else 385             event_del(ev); 386  387         /* Allows deletes to work */ 388         ncalls = ev->ev_ncalls; 389         ev->ev_pncalls = &ncalls; 390         while (ncalls) { 391             ncalls--; 392             ev->ev_ncalls = ncalls; 393             (*ev->ev_callback)((int)ev->ev_fd, ev->ev_res, ev->ev_arg); 394             if (event_gotsig || base->event_break) 395                 return; 396         } 397     } 398 }

注意382行，这一行可以发现，在自己添加event的时候，如果不是 EV_PERSIST，那么在这个event被响应一次，下一次这个event会被自动删除。event_process_active已经是处理事件了，但是添加事件实在timeout_process.

 void 924 timeout_process(struct event_base *base) 925 { 926     struct timeval now; 927     struct event *ev; 928  929     if (min_heap_empty(&base->timeheap)) 930         return; 931  932     gettime(base, &now); 933  934     while ((ev = min_heap_top(&base->timeheap))) { 935         if (evutil_timercmp(&ev->ev_timeout, &now, >)) 936             break; 937  938         /* delete this event from the I/O queues */ 939         event_del(ev); 940  941         event_debug(("timeout_process: call %p", 942              ev->ev_callback)); 943         event_active(ev, EV_TIMEOUT, 1); 944     } 945 }

 
943行标志着这个事件已经被添加到激活链表中了，这个函数调用了insert函数