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poll(2) [osx man page]

POLL(2) 						      BSD System Calls Manual							   POLL(2)

NAME
poll -- synchronous I/O multiplexing SYNOPSIS
#include <poll.h> int poll(struct pollfd fds[], nfds_t nfds, int timeout); DESCRIPTION
Poll() examines a set of file descriptors to see if some of them are ready for I/O or if certain events have occurred on them. The fds argu- ment is a pointer to an array of pollfd structures, as defined in <poll.h> (shown below). The nfds argument specifies 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. events Events to poll for. (See below.) revents Events which may occur or have occurred. (See below.) The event bitmasks in events and revents have the following bits: POLLERR An exceptional condition has occurred on the device or socket. This flag is output only, and ignored if present in the input events bitmask. POLLHUP The device or socket has been disconnected. This flag is output only, and ignored if present in the input events bitmask. Note that POLLHUP and POLLOUT are mutually exclusive and should never be present in the revents bitmask at the same time. POLLIN Data other than high priority data may be read without blocking. This is equivalent to ( POLLRDNORM | POLLRDBAND ). POLLNVAL The file descriptor is not open. This flag is output only, and ignored if present in the input events bitmask. POLLOUT Normal data may be written without blocking. This is equivalent to POLLWRNORM. POLLPRI High priority data may be read without blocking. POLLRDBAND Priority data may be read without blocking. POLLRDNORM Normal data may be read without blocking. POLLWRBAND Priority data may be written without blocking. POLLWRNORM Normal data may be written without blocking. The distinction between normal, priority, and high-priority data is specific to particular file types or devices. If timeout is greater than zero, it specifies a maximum interval (in milliseconds) to wait for any file descriptor to become ready. If timeout is zero, then poll() will return without blocking. If the value of timeout is -1, the poll blocks indefinitely. RETURN VALUES
Poll() 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 call, the fds array will be unmodified and the global variable errno will be set to indicate the error. ERRORS
Poll() will fail if: [EAGAIN] Allocation of internal data structures fails. A subsequent request may succeed. [EFAULT] Fds points outside the process's allocated address space. [EINTR] A signal is delivered before the time limit expires and before any of the selected events occurs. [EINVAL] The nfds argument is greater than OPEN_MAX or the timeout argument is less than -1. BUGS
The poll() system call currently does not support devices. SEE ALSO
accept(2), connect(2), kevent(2), read(2), recv(2), select(2), send(2), write(2) HISTORY
The poll() function call appeared in AT&T System V UNIX. BSD
February 27, 2005 BSD

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poll.h(3HEAD)							      Headers							     poll.h(3HEAD)

NAME
poll.h, poll - definitions for the poll() function SYNOPSIS
#include <poll.h> DESCRIPTION
The <poll.h> header defines the pollfd structure, which includes the following members: int fd the following descriptor being polled short events the input event flags (see below) short revents the output event flags (see below) The <poll.h> header defines the following type through typedef: nfds_t an unsigned integer type used for the number of file descriptors The implementation supports one or more programming environments in which the width of nfds_t is no greater than the width of type long. The names of these programming environments can be obtained using the confstr() function or the getconf utility. See confstr(3C) and get- conf(1). The following symbolic constants are defined, zero or more of which can be OR'ed together to form the events or revents members in the pollfd structure: POLLIN Data other than high-priority data can be read without blocking. POLLRDNORM Normal data can be read without blocking. POLLRDBAND Priority data can be read without blocking. POLLPRI High priority data can be read without blocking. POLLOUT Normal data can be written without blocking. POLLWRNORM Equivalent to POLLOUT. POLLWRBAND Priority data can be written. POLLERR An error has occurred (revents only). POLLHUP Device has been disconnected (revents only). POLLNVAL Invalid fd member (revents only). The significance and semantics of normal, priority, and high-priority data are file and device-specific. ATTRIBUTES
See attributes(5) for descriptions of the following attributes: +-----------------------------+-----------------------------+ | ATTRIBUTE TYPE | ATTRIBUTE VALUE | +-----------------------------+-----------------------------+ |Interface Stability |Standard | +-----------------------------+-----------------------------+ SEE ALSO
getconf(1), poll(2), confstr(3C), attributes(5), standards(5) SunOS 5.11 9 Sep 2004 poll.h(3HEAD)

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