1IO::Select(3pm)        Perl Programmers Reference Guide        IO::Select(3pm)
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NAME

6       IO::Select - OO interface to the select system call
7

SYNOPSIS

9           use IO::Select;
10
11           $s = IO::Select->new();
12
13           $s->add(\*STDIN);
14           $s->add($some_handle);
15
16           @ready = $s->can_read($timeout);
17
18           @ready = IO::Select->new(@handles)->can_read(0);
19

DESCRIPTION

21       The "IO::Select" package implements an object approach to the system
22       "select" function call. It allows the user to see what IO handles, see
23       IO::Handle, are ready for reading, writing or have an exception
24       pending.
25

CONSTRUCTOR

27       new ( [ HANDLES ] )
28           The constructor creates a new object and optionally initialises it
29           with a set of handles.
30

METHODS

32       add ( HANDLES )
33           Add the list of handles to the "IO::Select" object. It is these
34           values that will be returned when an event occurs. "IO::Select"
35           keeps these values in a cache which is indexed by the "fileno" of
36           the handle, so if more than one handle with the same "fileno" is
37           specified then only the last one is cached.
38
39           Each handle can be an "IO::Handle" object, an integer or an array
40           reference where the first element is an "IO::Handle" or an integer.
41
42       remove ( HANDLES )
43           Remove all the given handles from the object. This method also
44           works by the "fileno" of the handles. So the exact handles that
45           were added need not be passed, just handles that have an equivalent
46           "fileno"
47
48       exists ( HANDLE )
49           Returns a true value (actually the handle itself) if it is present.
50           Returns undef otherwise.
51
52       handles
53           Return an array of all registered handles.
54
55       can_read ( [ TIMEOUT ] )
56           Return an array of handles that are ready for reading.  "TIMEOUT"
57           is the maximum amount of time to wait before returning an empty
58           list (with $!  unchanged), in seconds, possibly fractional.  If
59           "TIMEOUT" is not given and any handles are registered then the call
60           will block indefinitely.  Upon error, an empty list is returned,
61           with $! set to indicate the error.  To distinguish between timeout
62           and error, set $! to zero before calling this method, and check it
63           after an empty list is returned.
64
65       can_write ( [ TIMEOUT ] )
66           Same as "can_read" except check for handles that can be written to.
67
68       has_exception ( [ TIMEOUT ] )
69           Same as "can_read" except check for handles that have an exception
70           condition, for example pending out-of-band data.
71
72       count ()
73           Returns the number of handles that the object will check for when
74           one of the "can_" methods is called or the object is passed to the
75           "select" static method.
76
77       bits()
78           Return the bit string suitable as argument to the core select()
79           call.
80
81       select ( READ, WRITE, EXCEPTION [, TIMEOUT ] )
82           "select" is a static method, that is you call it with the package
83           name like "new". "READ", "WRITE" and "EXCEPTION" are either "undef"
84           or "IO::Select" objects. "TIMEOUT" is optional and has the same
85           effect as for the core select call.
86
87           If at least one handle is ready for the specified kind of
88           operation, the result will be an array of 3 elements, each a
89           reference to an array which will hold the handles that are ready
90           for reading, writing and have exceptions respectively.  Upon
91           timeout, an empty list is returned, with $! unchanged.  Upon error,
92           an empty list is returned, with $!  set to indicate the error.  To
93           distinguish between timeout and error, set $! to zero before
94           calling this method, and check it after an empty list is returned.
95

EXAMPLE

97       Here is a short example which shows how "IO::Select" could be used to
98       write a server which communicates with several sockets while also
99       listening for more connections on a listen socket
100
101           use IO::Select;
102           use IO::Socket;
103
104           $lsn = IO::Socket::INET->new(Listen => 1, LocalPort => 8080);
105           $sel = IO::Select->new( $lsn );
106
107           while(@ready = $sel->can_read) {
108               foreach $fh (@ready) {
109                   if($fh == $lsn) {
110                       # Create a new socket
111                       $new = $lsn->accept;
112                       $sel->add($new);
113                   }
114                   else {
115                       # Process socket
116
117                       # Maybe we have finished with the socket
118                       $sel->remove($fh);
119                       $fh->close;
120                   }
121               }
122           }
123

AUTHOR

125       Graham Barr. Currently maintained by the Perl Porters.  Please report
126       all bugs to <perlbug@perl.org>.
127
129       Copyright (c) 1997-8 Graham Barr <gbarr@pobox.com>. All rights
130       reserved.  This program is free software; you can redistribute it
131       and/or modify it under the same terms as Perl itself.
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135perl v5.32.1                      2021-05-31                   IO::Select(3pm)
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