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epoll overview

epoll API Reference¶

#include <sys/epoll.h>

Core APIs¶

int epoll_create1(int flags);
int epoll_ctl(int epfd, int op, int fd, struct epoll_event *event);
int epoll_wait(int epfd, struct epoll_event *events, int maxevents, int timeout);

Common Flags¶

Flag	Usage
`EPOLL_CLOEXEC`	Close epoll fd across `exec()`
`EPOLLIN`	fd is readable
`EPOLLOUT`	fd is writable
`EPOLLERR`	error condition
`EPOLLHUP`	hang-up condition
`EPOLLET`	edge-triggered mode

Common Operations¶

Operation	Purpose
`EPOLL_CTL_ADD`	Add fd to epoll set
`EPOLL_CTL_MOD`	Modify monitored events
`EPOLL_CTL_DEL`	Remove fd from epoll set

Return Value¶

API	Success	Failure
`epoll_create1()`	epoll fd	`-1`, sets `errno`
`epoll_ctl()`	`0`	`-1`, sets `errno`
`epoll_wait()`	number of ready events	`-1`, sets `errno`

Minimal Example¶

int epfd = epoll_create1(EPOLL_CLOEXEC);
struct epoll_event ev;

ev.events = EPOLLIN;
ev.data.fd = fd;
epoll_ctl(epfd, EPOLL_CTL_ADD, fd, &ev);

Common Pitfalls¶

Use non-blocking fds in event loops.
Handle EINTR from epoll_wait().
Handle EPOLLERR and EPOLLHUP.
Remove or close fds carefully to avoid stale ownership.

epoll