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. */
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 */
if (mask & AE_READABLE) ee.events |= EPOLLIN;
if (mask & AE_WRITABLE) ee.events |= EPOLLOUT;
if (mask & AE_EXCEPTION) ee.events |= EPOLLPRI;