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>POLL(2)                       System Calls Manual                      POLL(2)
 
NAME
     poll - synchronous I/O multiplexing
 
SYNOPSIS
     #include &lt;poll.h&#62;
 
     int
     poll(struct pollfd *fds, int nfds, int timeout);
 
DESCRIPTION
     poll() provides a mechanism for reporting I/O conditions across a set of
     file descriptors.
 
     The arguments are as follows:
 
     fds      Points to an array of pollfd structures, which are defined as:
 
                    struct pollfd {
                            int fd;
                            short events;
                            short revents;
                    };
 
              The fd member is an open file descriptor.  The events and
              revents members are bitmasks of conditions to monitor and condi-
              tions found, respectively.
 
     nfds     The number of pollfd structures in the array.
 
     timeout  Maximum interval to wait for the poll to complete, in millisec-
              onds.  If this value is 0, then poll() will return immediately.
              If this value is INFTIM (-1), poll() will block indefinitely
              until a condition is found.
 
     The calling process sets the events bitmask and poll() sets the revents
     bitmask.  Each call to poll() resets the revents bitmask for accuracy.
     The condition flags in the bitmasks are defined as:
 
     POLLIN      Data is available on the file descriptor for reading.
 
     POLLNORM    Same as POLLIN.
 
     POLLPRI     Same as POLLIN.
 
     POLLOUT     Data can be written to the file descriptor without blocking.
 
     POLLERR     This flag is not used in this implementation and is provided
                 only for source code compatibility.
 
     POLLHUP     The file descriptor was valid before the polling process and
                 invalid after.  Presumably, this means that the file descrip-
                 tor was closed sometime during the poll.
 
     POLLNVAL    The corresponding file descriptor is invalid.
 
     POLLRDNORM  Same as POLLIN.
 
     POLLRDBAND  Same as POLLIN.
 
     POLLWRNORM  Same as POLLOUT.
 
     POLLWRBAND  Same as POLLOUT.
 
     POLLMSG     This flag is not used in this implementation and is provided
                 only for source code compatibility.
 
     All flags except POLLIN, POLLOUT, and their synonyms are for use only in
     the revents member of the pollfd structure.  An attempt to set any of
     these flags in the events member will generate an error condition.
 
     In addition to I/O multiplexing, poll() can be used to generate simple
     timeouts.  This functionality may be achieved by passing a null pointer
     for fds.
 
WARNINGS
     The POLLHUP flag is only a close approximation and may not always be
     accurate.
 
RETURN VALUES
     Upon error, poll() returns a -1 and sets the global variable errno to
     indicate the error.  If the timeout interval was reached before any
     events occurred, a 0 is returned.  Otherwise, poll() returns the number
     of file descriptors for which revents is non-zero.
 
ERRORS
     poll() will fail if:
 
     [EINVAL]   nfds was either a negative number or greater than the number
                of available file descriptors.
 
     [EINVAL]   An invalid flags was set in the events member of the pollfd
                structure.
 
     [EINVAL]   The timeout passed to poll() was too large.
 
     [EAGAIN]   Resource allocation failed inside of poll().  Subsequent calls
                to poll() may succeed.
 
     [EINTR]    poll() caught a signal during the polling process.
 
SEE ALSO
     poll(2), select(2), sysconf(3)
 
HISTORY
     A poll() system call appeared in AT&amp;T System V UNIX.
 
BSD                            December 13, 1994                           BSD
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1	28	unneback	`<!-- Copyright (C) 2003 Red Hat, Inc. -->`
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3			`<!-- and conditions set forth in the Open Publication License, v1.0 -->`
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85			`NAME="NET-COMMON-TCPIP-MANPAGES-POLL">poll</H1`
86			`><TABLE`
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93			`CLASS="SCREEN"`
94			`>POLL(2) System Calls Manual POLL(2)`
95
96			`NAME`
97			`poll - synchronous I/O multiplexing`
98
99			`SYNOPSIS`
100			`#include <poll.h>`
101
102			`int`
103			`poll(struct pollfd *fds, int nfds, int timeout);`
104
105			`DESCRIPTION`
106			`poll() provides a mechanism for reporting I/O conditions across a set of`
107			`file descriptors.`
108
109			`The arguments are as follows:`
110
111			`fds Points to an array of pollfd structures, which are defined as:`
112
113			`struct pollfd {`
114			`int fd;`
115			`short events;`
116			`short revents;`
117			`};`
118
119			`The fd member is an open file descriptor. The events and`
120			`revents members are bitmasks of conditions to monitor and condi-`
121			`tions found, respectively.`
122
123			`nfds The number of pollfd structures in the array.`
124
125			`timeout Maximum interval to wait for the poll to complete, in millisec-`
126			`onds. If this value is 0, then poll() will return immediately.`
127			`If this value is INFTIM (-1), poll() will block indefinitely`
128			`until a condition is found.`
129
130			`The calling process sets the events bitmask and poll() sets the revents`
131			`bitmask. Each call to poll() resets the revents bitmask for accuracy.`
132			`The condition flags in the bitmasks are defined as:`
133
134			`POLLIN Data is available on the file descriptor for reading.`
135
136			`POLLNORM Same as POLLIN.`
137
138			`POLLPRI Same as POLLIN.`
139
140			`POLLOUT Data can be written to the file descriptor without blocking.`
141
142			`POLLERR This flag is not used in this implementation and is provided`
143			`only for source code compatibility.`
144
145			`POLLHUP The file descriptor was valid before the polling process and`
146			`invalid after. Presumably, this means that the file descrip-`
147			`tor was closed sometime during the poll.`
148
149			`POLLNVAL The corresponding file descriptor is invalid.`
150
151			`POLLRDNORM Same as POLLIN.`
152
153			`POLLRDBAND Same as POLLIN.`
154
155			`POLLWRNORM Same as POLLOUT.`
156
157			`POLLWRBAND Same as POLLOUT.`
158
159			`POLLMSG This flag is not used in this implementation and is provided`
160			`only for source code compatibility.`
161
162			`All flags except POLLIN, POLLOUT, and their synonyms are for use only in`
163			`the revents member of the pollfd structure. An attempt to set any of`
164			`these flags in the events member will generate an error condition.`
165
166			`In addition to I/O multiplexing, poll() can be used to generate simple`
167			`timeouts. This functionality may be achieved by passing a null pointer`
168			`for fds.`
169
170			`WARNINGS`
171			`The POLLHUP flag is only a close approximation and may not always be`
172			`accurate.`
173
174			`RETURN VALUES`
175			`Upon error, poll() returns a -1 and sets the global variable errno to`
176			`indicate the error. If the timeout interval was reached before any`
177			`events occurred, a 0 is returned. Otherwise, poll() returns the number`
178			`of file descriptors for which revents is non-zero.`
179
180			`ERRORS`
181			`poll() will fail if:`
182
183			`[EINVAL] nfds was either a negative number or greater than the number`
184			`of available file descriptors.`
185
186			`[EINVAL] An invalid flags was set in the events member of the pollfd`
187			`structure.`
188
189			`[EINVAL] The timeout passed to poll() was too large.`
190
191			`[EAGAIN] Resource allocation failed inside of poll(). Subsequent calls`
192			`to poll() may succeed.`
193
194			`[EINTR] poll() caught a signal during the polling process.`
195
196			`SEE ALSO`
197			`poll(2), select(2), sysconf(3)`
198
199			`HISTORY`
200			`A poll() system call appeared in AT&T System V UNIX.`
201
202			`BSD December 13, 1994 BSD`
203			`</PRE`
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