NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | VERSIONS | CONFORMING TO | SEE ALSO | COLOPHON
EPOLL_WAIT(2) Linux Programmer's Manual EPOLL_WAIT(2)
epoll_wait, epoll_pwait - wait for an I/O event on an epoll file descriptor
#include <sys/epoll.h>
int epoll_wait(int epfd, struct epoll_event *events,
int maxevents, int timeout);
int epoll_pwait(int epfd, struct epoll_event *events,
int maxevents, int timeout,
const sigset_t *sigmask);
The epoll_wait() system call waits for events on the epoll instance referred
to by the file descriptor epfd. 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(). The maxevents argument must be greater than zero.
The call waits for a maximum time of timeout milliseconds. Specifying a
timeout of -1 makes epoll_wait() wait indefinitely, while specifying a timeout
equal to zero makes epoll_wait() 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 an epoll_ctl(2) (EPOLL_CTL_ADD,EPOLL_CTL_MOD) while the events member
will contain the returned event bit field.
The relationship between epoll_wait() and epoll_pwait() is analogous to the
relationship between select(2) and pselect(2): like pselect(2), epoll_pwait()
allows an application to safely wait until either a file descriptor becomes
ready or until a signal is caught.
The following epoll_pwait() call:
ready = epoll_pwait(epfd, &events, maxevents, timeout, &sigmask);
is equivalent to atomically executing the following calls:
sigset_t origmask;
sigprocmask(SIG_SETMASK, &sigmask, &origmask);
ready = epoll_wait(epfd, &events, maxevents, timeout);
sigprocmask(SIG_SETMASK, &origmask, NULL);
The sigmask argument may be specified as NULL, in which case epoll_pwait() is
equivalent to epoll_wait().
When successful, epoll_wait() 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() returns -1
and errno is set appropriately.
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; see signal(7).
EINVAL epfd is not an epoll file descriptor, or maxevents is less than or
equal to zero.
epoll_pwait() was added to Linux in kernel 2.6.19.
Glibc support for epoll_pwait() is provided starting with version 2.6.
epoll_wait() is Linux-specific, and was introduced in kernel 2.5.44.
epoll_create(2), epoll_ctl(2), epoll(7)
This page is part of release 3.23 of the Linux man-pages project. A
description of the project, and information about reporting bugs, can be found
at http://www.kernel.org/doc/man-pages/.
Linux 2009-01-17 EPOLL_WAIT(2)