DOKK / manpages / debian 12 / libio-async-perl / IO::Async::Loop::Select.3pm.en
IO::Async::Loop::Select(3pm) User Contributed Perl Documentation IO::Async::Loop::Select(3pm)

"IO::Async::Loop::Select" - use IO::Async with "select(2)"

Normally an instance of this class would not be directly constructed by a program. It may however, be useful for runinng IO::Async with an existing program already using a "select" call.

   use IO::Async::Loop::Select;
   my $loop = IO::Async::Loop::Select->new;
   $loop->add( ... );
   while(1) {
      my ( $rvec, $wvec, $evec ) = ('') x 3;
      my $timeout;
      $loop->pre_select( \$rvec, \$wvec, \$evec, \$timeout );
      ...
      my $ret = select( $rvec, $wvec, $evec, $timeout );
      ...
      $loop->post_select( $rvec, $evec, $wvec );
   }

This subclass of IO::Async::Loop uses the select(2) syscall to perform read-ready and write-ready tests.

To integrate with an existing "select"-based event loop, a pair of methods "pre_select" and "post_select" can be called immediately before and after a "select" call. The relevant bits in the read-ready, write-ready and exceptional-state bitvectors are set by the "pre_select" method, and tested by the "post_select" method to pick which event callbacks to invoke.

   $loop = IO::Async::Loop::Select->new

This function returns a new instance of a "IO::Async::Loop::Select" object. It takes no special arguments.

   $loop->pre_select( \$readvec, \$writevec, \$exceptvec, \$timeout )

This method prepares the bitvectors for a "select" call, setting the bits that the Loop is interested in. It will also adjust the $timeout value if appropriate, reducing it if the next event timeout the Loop requires is sooner than the current value.

\$readvec
\$writevec
\$exceptvec
Scalar references to the reading, writing and exception bitvectors
\$timeout
Scalar reference to the timeout value

   $loop->post_select( $readvec, $writevec, $exceptvec )

This method checks the returned bitvectors from a "select" call, and calls any of the callbacks that are appropriate.

$readvec
$writevec
$exceptvec
Scalars containing the read-ready, write-ready and exception bitvectors

   $count = $loop->loop_once( $timeout )

This method calls the "pre_select" method to prepare the bitvectors for a "select" syscall, performs it, then calls "post_select" to process the result. It returns the total number of callbacks invoked by the "post_select" method, or "undef" if the underlying select(2) syscall returned an error.

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IO::Select - OO interface to select system call

Paul Evans <leonerd@leonerd.org.uk>

2022-08-19 perl v5.34.0