IO::Select(3p) Perl Programmers Reference Guide IO::Select(3p)
IO::Select - OO interface to the select system call
use IO::Select;
$s = IO::Select->new();
$s->add(\*STDIN);
$s->add($some_handle);
@ready = $s->can_read($timeout);
@ready = IO::Select->new(@handles)->can_read(0);
The "IO::Select" package implements an object approach to
the system "select" function call. It allows the user to see
what IO handles, see IO::Handle, are ready for reading,
writing or have an exception pending.
new ( [ HANDLES ] )
The constructor creates a new object and optionally ini-
tialises it with a set of handles.
add ( HANDLES )
Add the list of handles to the "IO::Select" object. It
is these values that will be returned when an event
occurs. "IO::Select" keeps these values in a cache which
is indexed by the "fileno" of the handle, so if more
than one handle with the same "fileno" is specified then
only the last one is cached.
Each handle can be an "IO::Handle" object, an integer or
an array reference where the first element is an
"IO::Handle" or an integer.
remove ( HANDLES )
Remove all the given handles from the object. This
method also works by the "fileno" of the handles. So the
exact handles that were added need not be passed, just
handles that have an equivalent "fileno"
exists ( HANDLE )
Returns a true value (actually the handle itself) if it
is present. Returns undef otherwise.
handles
Return an array of all registered handles.
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IO::Select(3p) Perl Programmers Reference Guide IO::Select(3p)
can_read ( [ TIMEOUT ] )
Return an array of handles that are ready for reading.
"TIMEOUT" is the maximum amount of time to wait before
returning an empty list, in seconds, possibly frac-
tional. If "TIMEOUT" is not given and any handles are
registered then the call will block.
can_write ( [ TIMEOUT ] )
Same as "can_read" except check for handles that can be
written to.
has_exception ( [ TIMEOUT ] )
Same as "can_read" except check for handles that have an
exception condition, for example pending out-of-band
data.
count ()
Returns the number of handles that the object will check
for when one of the "can_" methods is called or the
object is passed to the "select" static method.
bits()
Return the bit string suitable as argument to the core
select() call.
select ( READ, WRITE, EXCEPTION [, TIMEOUT ] )
"select" is a static method, that is you call it with
the package name like "new". "READ", "WRITE" and "EXCEP-
TION" are either "undef" or "IO::Select" objects.
"TIMEOUT" is optional and has the same effect as for the
core select call.
The result will be an array of 3 elements, each a refer-
ence to an array which will hold the handles that are
ready for reading, writing and have exceptions respec-
tively. Upon error an empty list is returned.
Here is a short example which shows how "IO::Select" could
be used to write a server which communicates with several
sockets while also listening for more connections on a
listen socket
use IO::Select;
use IO::Socket;
$lsn = new IO::Socket::INET(Listen => 1, LocalPort => 8080);
$sel = new IO::Select( $lsn );
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IO::Select(3p) Perl Programmers Reference Guide IO::Select(3p)
while(@ready = $sel->can_read) {
foreach $fh (@ready) {
if($fh == $lsn) {
# Create a new socket
$new = $lsn->accept;
$sel->add($new);
}
else {
# Process socket
# Maybe we have finished with the socket
$sel->remove($fh);
$fh->close;
}
}
}
Graham Barr. Currently maintained by the Perl Porters.
Please report all bugs to <perl5-porters@perl.org>.
Copyright (c) 1997-8 Graham Barr <gbarr@pobox.com>. All
rights reserved. This program is free software; you can
redistribute it and/or modify it under the same terms as
Perl itself.
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