5.12. request poll()

5.12.1. Name

request-poll - Wait for some event on a file descriptor

5.12.2. Synopsis

#include <sys/poll.h>
int poll(struct pollfd *ufds, unsigned int nfds, int timeout)

5.12.3. Arguments


List of file descriptor events to be watched


Number of file descriptor events at the *ufds array


Timeout to wait for events

5.12.4. Description

With the poll() function applications can wait for a request to complete.

On success poll() returns the number of file descriptors that have been selected (that is, file descriptors for which the revents field of the respective struct pollfd is non-zero). Request file descriptor set the POLLPRI flag in revents when the request was completed. When the function times out it returns a value of zero, on failure it returns -1 and the errno variable is set appropriately.

Attempting to poll for a request that is not yet queued will set the POLLERR flag in revents.

5.12.5. Return Value

On success, poll() returns the number of structures which have non-zero revents fields, or zero if the call timed out. On error -1 is returned, and the errno variable is set appropriately:


One or more of the ufds members specify an invalid file descriptor.


ufds references an inaccessible memory area.


The call was interrupted by a signal.


The nfds value exceeds the RLIMIT_NOFILE value. Use getrlimit() to obtain this value.