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Poe currently contains two layers. It will contain at least four
before the 1.00 release. Each successively higher layer relies on the
presence of the ones below it. Lower levels do not require higher
Layer 0 (done):
POE's lowest layer consists of two classes for cooperative,
event-driven multitasking.
POE::Kernel is the event dispatcher, with logic for select(2), delayed
events (alarms), and signal handling.
POE::Session is the unit of execution and ownership, like a process in
real operating systems. POE::Session instances are composed of event
handlers named after the events they accept from POE::Kernel.
For some applications, it may be easier to consider POE::Session
to be a generic state machines. Events handlers map to states,
and events signal state transitions. Considering it this way,
it's possible to have multiple threads of execution (outstanding
state transition events) within a single POE::Session.
Layer 1a (done but needs more subclasses):
This layer consists of classes that contain "integrated circuit" state
machines. These state machine subroutines do common, reusable things.
Their public interfaces are designed so they can interlock to perform
larger tasks. This layer is composed of three basic types:
Drivers. These classes move data into and out of filehandles.
Typically one end of a Driver is connected to a filehandle, and the
other end is attached to a filter.
For example, Driver::SysRW driver performs sysread() and
syswrite() operations.
Filters. These classes translate raw streams into cooked units of
data, and uncook data back into streams. They are most commonly
placed between a Driver and a POE::Session.
For example, Filter::Line translates between raw streams and
newline-delimited lines.
Filter::Reference translates between raw streams and object
references, allowing programs to share objects.
Wheels. These classes contain select(2) event handlers. They can
use Drivers to handle file activity and Filters to frame data.
For example, Wheel::ListenAccept is a generic TCP server.
Wheel::ReadWrite can be used on either end of a TCP socket.
Subclasses generally are interchangable. Wherever a Driver is needed,
just about any Driver should do. Wherever a Filter is needed, related
filters should also work.
Layer 1b and beyond (forthcoming):
The probability that a "b" layer will be implemented as it's outlined
here decreases in proportion to its number. Consider this vaporware
until proven innocent.
Layer 1b will be classes that provide persistent, MUD-like objects,
with MUD-like security, inheritance and referential integrity.
These objects' methods map neatly onto POE::Session event handlers.
Most of the basic object features (store, fetch, execute) will be
coded into object #0, the basic Object, so that they can be altered
(with care) during runtime.
Layer 2b will be a framework of layer 1b objects that duplicate
drivers, filters and wheels from layer 1a.
Layer 3b will be a MUD server written in Layer 1b and 2b objects.
It will provide commands to modify layer 1b objects. This will
allow further development to occur within the "MUD" interface.
Layer 4b will be interactive programs ('bots) written in layer
1b-3b objects.
Things become even fuzzier after this.
A Curses-based windowing interface, written in 1b and 2b objects.
An earlier version of this already exists as part of Serv+Face.
The morbidly curious can find Serv and Face at
POE::Session::Safe. This may be a POE::Session that runs in its own
Safe compartment. It would include a runtime library to replace
"unsafe" things with safe counterparts.
A high-level object scripting language. It should be translated
into native "Safe" Perl, and evaluated into bytecode on the fly.
POE::Session::Threaded. This would be a POE::Session that uses
real threads.
POE has been tested with Perl 5.004_04 on recent versions of Linux,
FreeBSD, and OS/2. For more detailed compatibility information,
please see <>.
POE is rumored to work on Windows and suspected to work on MacOS. If
someone could confirm or deny this, I would appreciate it.
POE requires: a recent IO bundle;
If available, it will take advantage of: Time::HiRes
It does not require threads or other 5.004_50+ features.
When using the Reference filter, POE requires or
The latest version of POE is in /authors/id/R/RC/RCAPUTO/ on your
favorite CPAN mirror.
Thanks to Artur Bergman <> (sky) for much
useful feedback, suggestions and contributions. Most of the changes
up to version 0.05 are a result of his tireless work.
To build and test this distribution, type:
perl Makefile.PL
make test
Actually, 'make test' doesn't do anything important. The real tests
exist within the F<tests> directory, and just happen to be examples of
how to use different parts of POE. Once everything looks good, it
can be installed by typing:
make install
-- Rocco Caputo /
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