=head1 NAME

Async::Interrupt - allow C/XS libraries to interrupt perl asynchronously

=head1 SYNOPSIS

 use Async::Interrupt;

=head1 DESCRIPTION

This module implements a single feature only of interest to advanced perl
modules, namely asynchronous interruptions (think "unix signals", which
are very similar).

Sometimes, modules wish to run code asynchronously (in another thread),
and then signal the perl interpreter on certain events. One common way is
to write some data to a pipe and use an event handling toolkit to watch
for I/O events. Another way is to send a signal. Those methods are slow,
and in the case of a pipe, also not asynchronous - it won't interrupt a
running perl interpreter.

This module implements asynchronous notifications that enable you to
signal running perl code form another thread, asynchronously, without
issuing syscalls.

=over 4

=cut

package Async::Interrupt;

BEGIN {
   $VERSION = '0.02';

   require XSLoader;
   XSLoader::load Async::Interrupt::, $VERSION;
}

=item $async = new Async::Interrupt key => value...

Creates a new Async::Interrupt object. You may only use async
notifications on this object while it exists, so you need to keep a
reference to it at all times while it is used.

Optional constructor arguments include (normally you would specify at
least one of C<cb> or C<c_cb>).

=over 4

=item cb => $coderef->($value)

Registers a perl callback to be invoked whenever the async interrupt is
signalled.

Note that, since this callback can be invoked at basically any time, it
must not modify any well-known global variables such as C<$/>, C<$@> or
C<$!>, without restoring them again before returning.

=item c_cb => [$c_func, $c_data]

Registers a C callback the be invoked whenever the async interrupt is
signalled.

The C callback must have the following prototype:

   void c_func (pTHX_ void *c_data, int value);

Both C<$c_func> and C<$c_data> must be specified as integers/IVs.

Note that, because the callback can be invoked at almost any time, you
have to be careful at saving and restoring global variables that Perl
might use, most notably C<errno>. The callback itself runs as part of the
perl context, so you can call any perl functions and modify any perl data
structures.

=item fh => $fileno_or_fh

Specifies a file descriptor (or file handle) that should be signalled
whenever the async interrupt is signalled. This means a single octet will
be written to it, and before the callback is being invoked, it will be
read again. Due to races, it is unlikely but possible that multiple octets
are written, therefore, it is recommended that the file handle is in
nonblocking mode.

(You can get a portable pipe and set non-blocking mode portably by using
e.g. L<AnyEvent::Util> from the L<AnyEvent> distro).

The object will keep a reference to the file handle.

This can be used to ensure that async notifications will interrupt event
frameworks as well.

=back

=cut

sub new {
   my ($class, %arg) = @_;

   my $self = _alloc $arg{cb}, @{$arg{c_cb}}[0,1], $arg{fh};
   bless \$self, $class
}

=item ($signal_func, $signal_arg) = $async->signal_cb

Returns the address of a function to call asynchronously. The function has
the following prototype and needs to be passed the specified C<$c_arg>,
which is a C<void *> cast to C<IV>:

   void (*signal_func) (void *signal_arg, int value)

An example call would look like:

   signal_func (signal_arg, 0);

The function is safe toc all from within signal and thread contexts, at
any time. The specified C<value> is passed to both C and Perl callback.

If the function is called while the Async::Interrupt object is already
signaled but before the callbacks are being executed, then the stored
C<value> is being overwritten. Due to the asynchronous nature of the code,
the C<value> can even be passed to two consecutive invocations of the
callback.

=item $async->signal ($value=0)

This signals the given async object from Perl code. Semi-obviously, this
will instantly trigger the callback invocation.

=cut

1;

=back

=head1 AUTHOR

 Marc Lehmann <schmorp@schmorp.de>
 http://home.schmorp.de/

=cut