c - maxevents parameter in epoll_wait() and the events array size -


in epoll usage, following:

struct epoll_event ev,events[20]; epfd=epoll_create(256); 。。。 nfds=epoll_wait(epfd,events,40,500);

some articles saying maxevents parameter in epoll_wait (namely 40 in epoll_wait(epfd,events,40,500);) should not exceed size parameter in epoll_create(namely 256).

i think maxevents parameter should not exceed 20 in ev, events[20], because events can registered 20 events elements; otherwise, if there 40 sockets active, happen?

btw, if register more 20 sockets , there more 20 active events(sockets), events array events[20] has 20 events, happen?

at single call of epoll_wait you'll @ receive many events have room for, of course events don't lost if there more queued -- you'll them @ later call. since you'll calling epoll_wait in loop anyway, shouldn't issue @ all.

the 1 interesting consideration can think of when have multiple threads read same epoll-fd concurrently. in case size of event array determines how many events handled single thread (i.e. smaller number might give greater parallelism).


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