epoll_pwait(2) - Linux man page

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.