漫话Redis源码之八十一

fd_set是网络编程中很重要的结构体，rfds是读描述集， wfds是写描述集合，这是使用需要非常清晰，看最后的select, 知道怎么样了吧：

#include <sys/select.h>
#include <string.h>
 
typedef struct aeApiState {
    fd_set rfds, wfds;
    /* We need to have a copy of the fd sets as it's not safe to reuse
     * FD sets after select(). */
    fd_set _rfds, _wfds;
} aeApiState;
 
static int aeApiCreate(aeEventLoop *eventLoop) {
    aeApiState *state = zmalloc(sizeof(aeApiState));
 
    if (!state) return -1;
    FD_ZERO(&state->rfds);
    FD_ZERO(&state->wfds);
    eventLoop->apidata = state;
    return 0;
}
 
static int aeApiResize(aeEventLoop *eventLoop, int setsize) {
    /* Just ensure we have enough room in the fd_set type. */
    if (setsize >= FD_SETSIZE) return -1;
    return 0;
}
 
static void aeApiFree(aeEventLoop *eventLoop) {
    zfree(eventLoop->apidata);
}
 
static int aeApiAddEvent(aeEventLoop *eventLoop, int fd, int mask) {
    aeApiState *state = eventLoop->apidata;
 
    if (mask & AE_READABLE) FD_SET(fd,&state->rfds);
    if (mask & AE_WRITABLE) FD_SET(fd,&state->wfds);
    return 0;
}
 
static void aeApiDelEvent(aeEventLoop *eventLoop, int fd, int mask) {
    aeApiState *state = eventLoop->apidata;
 
    if (mask & AE_READABLE) FD_CLR(fd,&state->rfds);
    if (mask & AE_WRITABLE) FD_CLR(fd,&state->wfds);
}
 
static int aeApiPoll(aeEventLoop *eventLoop, struct timeval *tvp) {
    aeApiState *state = eventLoop->apidata;
    int retval, j, numevents = 0;
 
    memcpy(&state->_rfds,&state->rfds,sizeof(fd_set));
    memcpy(&state->_wfds,&state->wfds,sizeof(fd_set));
 
    retval = select(eventLoop->maxfd+1,
                &state->_rfds,&state->_wfds,NULL,tvp);
    if (retval > 0) {
        for (j = 0; j <= eventLoop->maxfd; j++) {
            int mask = 0;
            aeFileEvent *fe = &eventLoop->events[j];
 
            if (fe->mask == AE_NONE) continue;
            if (fe->mask & AE_READABLE && FD_ISSET(j,&state->_rfds))
                mask |= AE_READABLE;
            if (fe->mask & AE_WRITABLE && FD_ISSET(j,&state->_wfds))
                mask |= AE_WRITABLE;
            eventLoop->fired[numevents].fd = j;
            eventLoop->fired[numevents].mask = mask;
            numevents++;
        }
    }
    return numevents;
}
 
static char *aeApiName(void) {
    return "select";
}