NAME

Reflex::Role::Writing - add buffered non-blocking syswrite() to a class

VERSION

This document describes version 0.100, released on April 02, 2017.

SYNOPSIS

TODO - Changed again. It would be stellar if I could include a different bit of code as a synopsis or something, huh?

        package OutputStreaming;
        use Reflex::Role;

        attribute_parameter handle       => "handle";
        callback_parameter  cb_error     => qw( on handle error );
        method_parameter    method_put   => qw( put handle _ );
        method_parameter    method_stop  => qw( stop handle _ );
        method_parameter    method_flush => qw( _flush handle writable );

        role {
                my $p = shift;

                my $att_handle         = $p->handle();
                my $cb_error  = $p->cb_error();

                with 'Reflex::Role::Writing' => {
                        handle        => $att_handle,
                        cb_error      => $p->cb_error(),
                        method_put    => $p->method_put(),
                        method_flush  => $p->method_flush(),
                };

                with 'Reflex::Role::Writable' => {
                        handle        => $att_handle,
                        cb_ready      => $p->method_flush(),
                };

DESCRIPTION

Reflex::Role::Readable implements a standard nonblocking sysread() feature so that it may be added to classes as needed.

There's a lot going on in the SYNOPSIS.

Reflex::Role::Writing defines methods that will perform non-blocking, buffered syswrite() on a named "handle". It has a single callback, "cb_error", that is invoked if syswrite() ever returns an error. It defines a method, "method_put", that is used to write new data to the handle---or buffer data if it can't be written immediately. "method_flush" is defined to flush buffered data when possible.

Reflex::Role::Writable implements the other side of the Writable/Writing contract. It wastches a "handle" and invokes "cb_ready" whenever the opportunity to write new data arises. It defines a few methods, two of which allow the watcher to be paused and resumed.

The Writable and Writing roles are generally complementary. Their defaults allow them to fit together more succinctly than (and less understandably than) shown in the SYNOPSIS.

Attribute Role Parameters

handle

"handle" names an attribute holding the handle to be watched for writable readiness.

Callback Role Parameters

cb_error

"cb_error" names the $self method that will be called whenever the stream produces an error. By default, this method will be the catenation of "on_", the "handle" name, and "_error". As in on_XYZ_error(), if the handle is named "XYZ". The role defines a default callback that will emit an "error" event with cb_error()'s parameters, then will call stopped() so that streams managed by Reflex::Collection will be automatically cleaned up after stopping.

"cb_error" callbacks receive two parameters, $self and an anonymous hashref of named values specific to the callback. Reflex error callbacks include three standard values. "errfun" contains a single word description of the function that failed. "errnum" contains the numeric value of $! at the time of failure. "errstr" holds the stringified version of $!.

Values of $! are passed as parameters since the global variable may change before the callback can be invoked.

When overriding this callback, please be sure to call stopped(), which is provided by Reflex::Role::Collectible. Calling stopped() is vital for collectible objects to be released from memory when managed by Reflex::Collection.

Method Role Parameters

method_put

This role genrates a method to write data to the handle in the "handle" attribute. The "method_put" role parameter specifies the name of this generated method. The method's name will be "put_${handle_name}" by default.

The generated method will immediately attempt to write data if the role's buffer is empty. If the buffer contains data, however, then the new data will be appended there to maintain the ordering of data in the stream. Any data that could not be written during "method_put" will be added to the buffer as well.

The "method_put" implementation will call "method_resume_writable" to enable background flushing, as needed.

The generated "method_put" will return a numeric code representing the current state of the role's output buffer. Undef if syswrite failed, after "cb_error" has been called. It returns 0 if the buffer is still empty after the syswrite(). It returns 1 if the buffer begins to contain data, or 2 if the buffer already contained data and now holds more.

The return code is intended to control Reflex::Role::Writable, via some glue code in the class or role that consumes both. When "method_put" returns 1, the consumer should begin triggering "method_flush" calls on writability callbacks. The consumer should stop writability callbacks when "method_flush" returns 0 (no more octets in the buffer).

method_flush

This role generates a method to flush data that had to be buffered by previous "method_put" calls. It's designed to be used with some kind of callback system, such as Reflex::Role::Writable's callbacks.

The "method_flush" implementation returns undef on error. It will return the number of octets remaining in the buffer, or zero if the buffer has been completely flushed.

The "method_flush" return value may be used to disable writability watchers, such as the one provided by Reflex::Role::Writable. See the source for Reflex::Role::Streaming for an up-to-date example.

TODO

There's always something.

EXAMPLES

Reflex::Role::Streaming is an up-to-date example.

BUGS AND LIMITATIONS

You can make new bug reports, and view existing ones, through the web interface at <http://rt.cpan.org/Public/Dist/Display.html?Name=Reflex>.

AUTHOR

Rocco Caputo <rcaputo@cpan.org>

COPYRIGHT AND LICENSE

This is free software; you can redistribute it and/or modify it under the same terms as the Perl 5 programming language system itself.

AVAILABILITY

The latest version of this module is available from the Comprehensive Perl Archive Network (CPAN). Visit <http://www.perl.com/CPAN/> to find a CPAN site near you, or see <https://metacpan.org/module/Reflex/>.

DISCLAIMER OF WARRANTY

BECAUSE THIS SOFTWARE IS LICENSED FREE OF CHARGE, THERE IS NO WARRANTY FOR THE SOFTWARE, TO THE EXTENT PERMITTED BY APPLICABLE LAW. EXCEPT WHEN OTHERWISE STATED IN WRITING THE COPYRIGHT HOLDERS AND/OR OTHER PARTIES PROVIDE THE SOFTWARE "AS IS" WITHOUT WARRANTY OF ANY KIND, EITHER EXPRESSED OR IMPLIED, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. THE ENTIRE RISK AS TO THE QUALITY AND PERFORMANCE OF THE SOFTWARE IS WITH YOU. SHOULD THE SOFTWARE PROVE DEFECTIVE, YOU ASSUME THE COST OF ALL NECESSARY SERVICING, REPAIR, OR CORRECTION.

IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN WRITING WILL ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MAY MODIFY AND/OR REDISTRIBUTE THE SOFTWARE AS PERMITTED BY THE ABOVE LICENCE, BE LIABLE TO YOU FOR DAMAGES, INCLUDING ANY GENERAL, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES ARISING OUT OF THE USE OR INABILITY TO USE THE SOFTWARE (INCLUDING BUT NOT LIMITED TO LOSS OF DATA OR DATA BEING RENDERED INACCURATE OR LOSSES SUSTAINED BY YOU OR THIRD PARTIES OR A FAILURE OF THE SOFTWARE TO OPERATE WITH ANY OTHER SOFTWARE), EVEN IF SUCH HOLDER OR OTHER PARTY HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES.