File descriptor to poll. If fd is equal to -1 then revents is cleared (set to zero), and that pollfd is not checked.
events
Events to poll for. (See below.)
revents
Events which may occur. (See below.)
The event bitmasks in events and revents have the following bits:
POLLIN
Data other than high priority data may be read without blocking.
POLLRDNORM
Normal data may be read without blocking.
POLLRDBAND
Data with a non-zero priority may be read without blocking.
POLLPRI
High priority data may be read without blocking.
POLLOUT POLLWRNORM
Normal data may be written without blocking.
POLLWRBAND
Data with a non-zero priority may be written without blocking.
POLLERR
An exceptional condition has occurred on the device or socket. This flag is always checked, even if not present in the events bitmask.
POLLHUP
The device or socket has been disconnected. This flag is always checked, even if not present in the events bitmask. Note that POLLHUP and POLLOUT should never be present in the revents bitmask at the same time.
POLLNVAL
The file descriptor is not open. This flag is always checked, even if not present in the events bitmask.
If timeout is neither zero nor INFTIM (-1), it specifies a maximum interval to wait for any file descriptor to become ready, in milliseconds. If timeout is INFTIM (-1), the poll blocks indefinitely. If timeout is zero, then poll will return without blocking.
