EPOLL_WAIT

Section: Linux Programmer's Manual (2)
Updated: 23 October 2002
Index Return to Main Contents

NAME

epoll_wait - wait for an I/O event on an epoll file descriptor

SYNOPSIS

#include <sys/epoll.h>

int epoll_wait(int epfd, struct epoll_event * events, int maxevents, int timeout)

DESCRIPTION

Wait for events on the epoll file descriptor epfd for a maximum time of timeout milliseconds. The memory area pointed to by events will contain the events that will be available for the caller. Up to maxevents are returned by epoll_wait(2). The maxevents parameter must be greater than zero. Specifying a timeout of -1 makes epoll_wait(2) wait indefinitely, while specifying a timeout equal to zero makes epoll_wait(2) to return immediately even if no events are available ( return code equal to zero ). The struct epoll_event is defined as :


        typedef union epoll_data {
                void *ptr;
                int fd;
                __uint32_t u32;
                __uint64_t u64;
        } epoll_data_t;

        struct epoll_event {
                __uint32_t events;      /* Epoll events */
                epoll_data_t data;      /* User data variable */
        };

The data of each returned structure will contain the same data the user set with a epoll_ctl(2) (EPOLL_CTL_ADD,EPOLL_CTL_MOD) while the events member will contain the returned event bit field.

RETURN VALUE

When successful, epoll_wait(2) returns the number of file descriptors ready for the requested I/O, or zero if no file descriptor became ready during the requested timeout milliseconds. When an error occurs, epoll_wait(2) returns -1 and errno is set appropriately.

ERRORS

EBADF: epfd is not a valid file descriptor.
EFAULT: The memory area pointed to by events is not accessible with write permissions.
EINTR: The call was interrupted by a signal handler before any of the requested events occurred or the timeout expired.
EINVAL: epfd is not an epoll file descriptor, or maxevents is less than or equal to zero.

CONFORMING TO

epoll_wait(2) is a new API introduced in Linux kernel 2.5.44. The interface should be finalized by Linux kernel 2.5.66.