IO::Select(3pm) Perl Programmers Reference Guide IO::Select(3pm)
NAME
IO::Select - OO interface to the select system call
SYNOPSIS
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);
DESCRIPTION
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.
CONSTRUCTOR
new ( [ HANDLES ] )
The constructor creates a new object and optionally initialises it
with a set of handles.
METHODS
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.
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 (with $! unchanged), in seconds, possibly fractional. If
"TIMEOUT" is not given and any handles are registered then the call
will block indefinitely. Upon error, an empty list is returned,
with $! set to indicate the error. To distinguish between timeout
and error, set $! to zero before calling this method, and check it
after an empty list is returned.
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 "EXCEPTION" are either "undef"
or "IO::Select" objects. "TIMEOUT" is optional and has the same
effect as for the core select call.
If at least one handle is ready for the specified kind of
operation, the result will be an array of 3 elements, each a
reference to an array which will hold the handles that are ready
for reading, writing and have exceptions respectively. Upon
timeout, an empty list is returned, with $! unchanged. Upon error,
an empty list is returned, with $! set to indicate the error. To
distinguish between timeout and error, set $! to zero before
calling this method, and check it after an empty list is returned.
EXAMPLE
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 = IO::Socket::INET->new(Listen => 1, LocalPort => 8080);
$sel = IO::Select->new( $lsn );
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;
}
}
}
AUTHOR
Graham Barr. Currently maintained by the Perl Porters. Please report
all bugs to <perlbug@perl.org>.
COPYRIGHT
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.
perl v5.28.1 2018-11-01 IO::Select(3pm)
perl 5.28.1 - Generated Sat Jan 12 16:01:10 CST 2019