explain_poll_or_die(3) Library Functions Manual explain_poll_or_die(3)NAME
explain_poll_or_die - wait for some event on file descriptor and report errors
SYNOPSIS
#include <libexplain/poll.h>
int explain_poll_or_die(struct pollfd *fds, int nfds, int timeout);
int explain_poll_on_error(struct pollfd *fds, int nfds, int timeout);
DESCRIPTION
The explain_poll_or_die function is used to call the poll(2) system call. On failure an explanation will be printed to stderr, obtained
from the explain_poll(3) function, and then the process terminates by calling exit(EXIT_FAILURE).
The explain_poll_on_error function is used to call the poll(2) system call. On failure an explanation will be printed to stderr, obtained
from the explain_poll(3) function, but still returns to the caller.
fds The fds, exactly as to be passed to the poll(2) system call.
nfds The nfds, exactly as to be passed to the poll(2) system call.
timeout The timeout, exactly as to be passed to the poll(2) system call.
RETURN VALUE
The explain_poll_or_die function only returns on success, see poll(2) for more information. On failure, prints an explanation and exits, it
does not return.
The explain_poll_on_error function always returns the value return by the wrapped poll(2) system call.
EXAMPLE
The explain_poll_or_die function is intended to be used in a fashion similar to the following example:
int result = explain_poll_or_die(fds, nfds, timeout);
SEE ALSO poll(2) wait for some event on a file descriptor
explain_poll(3)
explain poll(2) errors
exit(2) terminate the calling process
COPYRIGHT
libexplain version 0.52
Copyright (C) 2010 Peter Miller
explain_poll_or_die(3)
Check Out this Related Man Page
POLL(2) BSD System Calls Manual POLL(2)NAME
poll -- synchronous I/O multiplexing
LIBRARY
Standard C Library (libc, -lc)
SYNOPSIS
#include <poll.h>
int
poll(struct pollfd fds[], nfds_t nfds, int timeout);
int
ppoll(struct pollfd fds[], nfds_t nfds, const struct timespec * restrict timeout, const sigset_t * restrict newsigmask);
DESCRIPTION
The poll() system call examines a set of file descriptors to see if some of them are ready for I/O. The fds argument is a pointer to an
array of pollfd structures as defined in <poll.h> (shown below). The nfds argument determines the size of the fds array.
struct pollfd {
int fd; /* file descriptor */
short events; /* events to look for */
short revents; /* events returned */
};
The fields of struct pollfd are as follows:
fd 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.
The ppoll() system call, unlike poll(), is used to safely wait until either a set of file descriptors becomes ready or until a signal is
caught. The fds and nfds arguments are identical to the analogous arguments of poll(). The timeout argument in ppoll() points to a const
struct timespec which is defined in <sys/timespec.h> (shown below) rather than the int timeout used by poll(). A null pointer may be passed
to indicate that ppoll() should wait indefinitely. Finally, newsigmask specifies a signal mask which is set while waiting for input. When
ppoll() returns, the original signal mask is restored.
struct timespec {
time_t tv_sec; /* seconds */
long tv_nsec; /* and nanoseconds */
};
RETURN VALUES
The poll() system call returns the number of descriptors that are ready for I/O, or -1 if an error occurred. If the time limit expires,
poll() returns 0. If poll() returns with an error, including one due to an interrupted system call, the fds array will be unmodified.
COMPATIBILITY
This implementation differs from the historical one in that a given file descriptor may not cause poll() to return with an error. In cases
where this would have happened in the historical implementation (e.g. trying to poll a revoke(2)ed descriptor), this implementation instead
copies the events bitmask to the revents bitmask. Attempting to perform I/O on this descriptor will then return an error. This behaviour is
believed to be more useful.
ERRORS
An error return from poll() indicates:
[EFAULT] The fds argument points outside the process's allocated address space.
[EINTR] A signal was delivered before the time limit expired and before any of the selected events occurred.
[EINVAL] The specified time limit is invalid. One of its components is negative or too large.
SEE ALSO accept(2), connect(2), kqueue(2), pselect(2), read(2), recv(2), select(2), send(2), write(2)STANDARDS
The poll() function conforms to IEEE Std 1003.1-2001 (``POSIX.1''). The ppoll() is not specified by POSIX.
HISTORY
The poll() function appeared in AT&T System V UNIX. This manual page and the core of the implementation was taken from NetBSD. The ppoll()
function first appeared in FreeBSD 11.0
BUGS
The distinction between some of the fields in the events and revents bitmasks is really not useful without STREAMS. The fields are defined
for compatibility with existing software.
BSD November 13, 2014 BSD