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 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.
Return Value
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.
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; see signal(7).
EINVAL
epfd is not an epoll file descriptor, or maxevents is less than or
equal to zero.
Versions
epoll_wait() was added to the kernel in version 2.6. Library support is
provided in glibc starting with version 2.3.2.
Description
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 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.
Return Value
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.
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; see signal(7). EINVAL epfd is not an epoll file descriptor, or maxevents is less than or equal to zero.
Versions
epoll_wait() was added to the kernel in version 2.6. Library support is provided in glibc starting with version 2.3.2.