1 .\" $NetBSD: poll.2,v 1.3 1996/09/07 21:53:08 mycroft Exp $
4 .\" Copyright (c) 1996 Charles M. Hannum. All rights reserved.
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36 .Nd synchronous I/O multiplexing
42 .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 -width XXXrevents
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 -width XXXPOLLWRNORM
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.
106 flag is always checked, even if not present in the
110 The device or socket has been disconnected.
112 checked, even if not present in the
119 should never be present in the
121 bitmask at the same time.
123 The file descriptor is not open.
124 This flag is always checked, even
125 if not present in the
132 is neither zero nor INFTIM (-1), it specifies a maximum interval to
133 wait for any file descriptor to become ready, in milliseconds.
136 is INFTIM (-1), the poll blocks indefinitely.
141 will return without blocking.
146 returns the number of descriptors that are ready for I/O, or -1 if an
148 If the time limit expires,
153 returns with an error,
154 including one due to an interrupted system call,
157 array will be unmodified.
159 This implementation differs from the historical one in that a given
160 file descriptor may not cause
162 to return with an error.
163 In cases where this would have happened in
164 the historical implementation (e.g.\& trying to poll a
166 descriptor), this implementation instead copies the
171 Attempting to perform I/O on this descriptor will then
173 This behaviour is believed to be more useful.
183 points outside the process's allocated address space.
185 A signal was delivered before the time limit expired and
186 before any of the selected events occurred.
188 The specified time limit is negative.
204 This manual page and the core of the implementation was taken from
207 The distinction between some of the fields in the
211 bitmasks is really not useful without STREAMS.
213 defined for compatibility with existing software.