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 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.
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);
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.
epfd is not
a valid file descriptor.
The memory area pointed to by events is not accessible
with write permissions.
The call was interrupted by a signal handler before
any of the requested events occurred or the timeout expired.
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_create(2), epoll_ctl(2), epoll(7)
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