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epoll_wait() - Unix, Linux System Call
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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);
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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 */
};
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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
Tag | Description |
EBADF |
epfd is not a valid file descriptor.
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EFAULT |
The memory area pointed to by
events is not accessible with write permissions.
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EINTR |
The call was interrupted by a signal handler before any of the
requested events occurred or the
timeout expired.
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EINVAL |
epfd is not an
epoll file descriptor, or
maxevents is less than or equal to zero.
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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.
SEE ALSO
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