redis中io复用之epoll

前面讲过evport的实现，下来我们继续看看我们epoll在redis中的使用
1：首先通过epoll_create 来新建fd
例如：
typedef struct aeApiState {
int epfd;
struct epoll_event *events;
} aeApiState;
static int aeApiCreate(aeEventLoop *eventLoop) {
aeApiState *state = zmalloc(sizeof(aeApiState));

if (!state) return -1;
#为要监控的event申请空间
state->events = zmalloc(sizeof(struct epoll_event)*eventLoop->setsize);
if (!state->events) {
zfree(state);
return -1;
}
#通过epoll_create来新建1024个fd来提供给系统使用
state->epfd = epoll_create(1024); /* 1024 is just a hint for the kernel */
if (state->epfd == -1) {
zfree(state->events);
zfree(state);
return -1;
}
eventLoop->apidata = state;
return 0;
}
2：通过epoll_ctl来add/del event
static int aeApiAddEvent(aeEventLoop *eventLoop, int fd, int mask) {
aeApiState *state = eventLoop->apidata;
struct epoll_event ee;
/* If the fd was already monitored for some event, we need a MOD
* operation. Otherwise we need an ADD operation. */
#这里的op表示是添加event还是修改已经存在的event
int op = eventLoop->events[fd].mask == AE_NONE ?
EPOLL_CTL_ADD : EPOLL_CTL_MOD;

ee.events = 0;
mask |= eventLoop->events[fd].mask; /* Merge old events */
#监控读和写事件
if (mask & AE_READABLE) ee.events |= EPOLLIN;
if (mask & AE_WRITABLE) ee.events |= EPOLLOUT;
ee.data.u64 = 0; /* avoid valgrind warning */
#要监控的fd
ee.data.fd = fd;
#将前面设置好的epfd/op/fd/ee 通过epoll_ctl 设置到kernel space
if (epoll_ctl(state->epfd,op,fd,&ee) == -1) return -1;
return 0;
}
3：最后通过epoll_wait 来等待event时间的发生。
static int aeApiPoll(aeEventLoop *eventLoop, struct timeval *tvp) {
aeApiState *state = eventLoop->apidata;
int retval, numevents = 0;
#通过epoll_wait 等待epfd事件的发生，这里有设置timeout的时间，在规定的时间内epoll_wait 必须返回
retval = epoll_wait(state->epfd,state->events,eventLoop->setsize,
tvp ? (tvp->tv_sec*1000 + tvp->tv_usec/1000) : -1);
#retval大于0说明是有event发生了，如果是timeout返回则retval等于-1
if (retval > 0) {
int j;

numevents = retval;
#遍历state->events 数据分别找出是读还是写event
for (j = 0; j < numevents; j++) {
int mask = 0;
struct epoll_event *e = state->events+j;
#根据mask 判断是读还是写事件
if (e->events & EPOLLIN) mask |= AE_READABLE;
if (e->events & EPOLLOUT) mask |= AE_WRITABLE;
if (e->events & EPOLLERR) mask |= AE_WRITABLE;
if (e->events & EPOLLHUP) mask |= AE_WRITABLE;
#保持发生event的fd和保存fd对于的mask
eventLoop->fired[j].fd = e->data.fd;
eventLoop->fired[j].mask = mask;
}
}
return numevents;
}