1 .\" $NetBSD: poll.2,v 1.3 1996/09/07 21:53:08 mycroft Exp $
2 .\" $FreeBSD: src/lib/libc/sys/poll.2,v 1.4.2.3 2001/12/14 18:34:01 ru Exp $
3 .\" $DragonFly: src/lib/libc/sys/poll.2,v 1.7 2008/05/25 14:04:32 swildner Exp $
5 .\" Copyright (c) 1996 Charles M. Hannum. All rights reserved.
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37 .Nd synchronous I/O multiplexing
44 .Fn poll "struct pollfd *fds" "nfds_t nfds" "int timeout"
47 examines a set of file descriptors to see if some of them are ready for
51 argument is a pointer to an array of pollfd structures as defined in
56 argument determines the size of the
61 int fd; /* file descriptor */
62 short events; /* events to look for */
63 short revents; /* events returned */
70 .Bl -tag -offset indent -width ".Fa revents"
72 File descriptor to poll.
73 If fd is equal to -1 then
75 is cleared (set to zero), and that pollfd is not checked.
80 Events which may occur.
88 have the following bits:
89 .Bl -tag -offset indent -width ".Dv POLLRDNORM"
91 Data other than high priority data may be read without blocking.
93 Normal data may be read without blocking.
95 Data with a non-zero priority may be read without blocking.
97 High priority data may be read without blocking.
100 Normal data may be written without blocking.
102 Data with a non-zero priority may be written without blocking.
104 An exceptional condition has occurred on the device or socket.
105 This flag is always checked, even if not present in the
109 The device or socket has been disconnected.
110 This flag is always checked, even if not present in the
117 should never be present in the
119 bitmask at the same time.
121 The file descriptor is not open.
122 This flag is always checked, even if not present in the
131 it specifies a maximum interval to
132 wait for any file descriptor to become ready, in milliseconds.
137 the poll blocks indefinitely.
142 will return without blocking.
145 returns the number of descriptors that are ready for I/O, or -1 if an
147 If the time limit expires,
152 returns with an error,
153 including one due to an interrupted call,
156 array will be unmodified.
158 This implementation differs from the historical one in that a given
159 file descriptor may not cause
161 to return with an error.
162 In cases where this would have happened in the historical implementation
163 (e.g.\& trying to poll a
165 descriptor), this implementation instead copies the
170 Attempting to perform I/O on this descriptor will then return an error.
171 This behaviour is believed to be more useful.
179 points outside the process's allocated address space.
181 A signal was delivered before the time limit expired and
182 before any of the selected events occurred.
184 The specified time limit is negative.
197 function call appeared in
199 This manual page was taken from
202 The distinction between some of the fields in the
206 bitmasks is really not useful without STREAMS.
207 The fields are defined for compatibility with existing software.