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<H1>[MUD-Dev] DGD Description</H1>
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<LI><em>To</em>: <<A HREF="mailto:mud-dev#kanga,nu">mud-dev#kanga,nu</A>></LI>
<LI><em>Subject</em>: [MUD-Dev] DGD Description</LI>
<LI><em>From</em>: "Christopher Allen" <<A HREF="mailto:ChristopherA#Skotos,net">ChristopherA#Skotos,net</A>></LI>
<LI><em>Date</em>: Tue, 11 Apr 2000 12:55:41 -0700</LI>
<LI><em>Importance</em>: Normal</LI>
<LI><em>Reply-To</em>: <A HREF="mailto:mud-dev#kanga,nu">mud-dev#kanga,nu</A></LI>
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<PRE>
I was surprised at the Mud-Dev dinner that a number of people were not
familiar with DGD, so I thought that I would post this description of it.
------------------------------------------------------------------------
.. Christopher Allen Skotos Tech Inc. ..
.. 1512 Walnut St., Berkeley, CA 94709-1513 ..
.. <<A HREF="http://www.Skotos.net">http://www.Skotos.net</A>> o510/649-4030 f510/649-4034 ..
DGD - Dworkin's Generic Driver
==============================
DGD is an Internet server designed for extremely stable, high-
performance, multi-user Internet applications. DGD offers an object-
oriented run-time environment for a C/C++-like language known as LPC,
as well as an integrated, persistent object database. DGD benefits
from a highly efficient design; it runs on any modern Unix system and
has been ported to Win32, BeOS, and the Macintosh OS. Each of these
features makes DGD an ideal rapid-prototyping environment.
DGD has a long track record of proven performance in commercial and
non-commercial settings. DGD formed the foundation of iChat's ROOMS
system and powered Yahoo! Chat, which served thousands of users. DGD was
developed by and is maintained by Felix Croes since 1993; he continues
to update it with new features.
Architecturally DGD has a number of distinct parts:
* an object-oriented dialect of C/C++ named LPC, which supports rapid
prototyping;
* a compiler that translates LPC source code into internal minimalist
byte-code;
* a runtime environment that supports a tight interpreter loop for
said byte-code;
* an integrated, persistent database for gigabyte-sized object state
spaces;
* a built-in I/O API for file and network operations;* an extremely
powerful generic string parser; and
* a kernel LPC library that maintains security, stability and
extensibility
The LPC Language
----------------
The LPC language (also known as Pike) is an object-oriented dialect of
C/C++ designed to be intuitive yet powerful. LPC has a type system that
helps you write structured and disciplined code, yet is flexible enough
not to be constraining.
* object-oriented dialect of C/C++ supports multiple and private
inheritance
* LPC values have run-time type: int, float, string, array, mapping,
object
- strings are null-safe binary byte arrays
- dynamically resizable arrays support concatenation,
subtraction, union, and intersection; arrays are passed by
pointer, i.e. call-by-name
- mappings are associative arrays with O(lg N) look-up and
insertion complexities; mappings are passed by pointer, i.e.
call-by-name
- objects reference classes [programs] or instances [clones]
- objects are persistent and must be explicitly destructed, which
turns referencing values to nil
The LPC Compiler
----------------
LPC classes are compiled at run-time, and DGD supports in-place
recompilation. This means the server never needs to be shut down for
maintenance: all object code is "hot-swappable". For even higher
performance, the driver allows the compilation of LPC objects into raw C
source, which may then in turn be compiled and linked with DGD itself.
* peephole-optimizing run-time LPC compiler generates internal byte
code
* ability to recompile programs in-place with automatic data space
upgrading
* off-line LPC pre-compiler generates high-performance C source for
linking with the DGD binary itself
Runtime Environment
-------------------
DGD's runtime environment is built on stability and persistence. It
offers full system-state rollback and garbage collection via reference
counting deallocation mechanisms. Programs and clones can be compiled,
cloned, destroyed, and interrogated at runtime.
* atomic function calls allow full system-state rollback in the event
of a run-time error
* stack-machine interpreter loop executes byte code in many single
threads of short, restricted execution time
* reference-counting deallocation mechanism complemented by copying
garbage collection and periodic swap-outs of all objects to disk
with subsequent freeing of any remaining (circular) data structures
* global object namespace allow for named reference of programs and
their clones
SMP Support
-----------
The system design of DGD includes the planned capability to support
Symmetric Multi Processing (SMP) in near future. This allows for
development of code today that will work with multiple processors in the
future.
* multi-threaded execution of the single-threaded LPC environment
using the 'atomic' functionality to rollback system-wide changes when
threads conflict in resource usage
Database
--------
DGD maintains persistence as a characteristic of its runtime
environment. It does this through an integral database without any
internal or external separation of functionality. Object swapping allows
for gigabyte-sized databases.
* full system state dump files implement persistence across reboots
as well as snapshot-style state backups using fast database copy
without forking
* seamless object swapping mechanisms allow for smoothly running
systems with states exceeding machine capacity by orders of magnitude
* the mapping data type allows for rapid (O(lg N)) data lookup within
objects
I/O API
-------
DGD's built-in I/O functionality provides for network and file
operations. TCP and UDP are fully supported; ports and sockets are
associated with DGD objects. All standard file access functions are
available, including the ability to modify and query files and
directories.
* networking functionality includes ability to:
- open a TCP port and associate it with an object; asynchronous
connection attempts communicated through a call-back system
- accept a connection, create a socket, and associate it with an
object; similarly call-back based
- open a UDP port and associate it with an object; asynchronous
datagram input communicated through a call-back system
- create outbound TCP connection attempts
- send outbound UDP datagrams
* file access functionality includes ability to:
- write/read a range of bytes from/into a file
- read the names, modification times, and sizes of the contents of
a directory
- delete or rename a file or directory
- create a directory
String Parsing
--------------
DGD's string parser deconstructs text input according to the rules of a
given formal grammar. The parser is more powerful than programming
language compilers; its ability to accept a potentially ambiguous
grammar makes it ideal for analyzing natural languages e.g. English
sentences.
* Tomita general LR parsing technique
* generic run-time parsing ability based on BNF-style formal grammars
* lazy construction of tokenization DFA and compressed parser PDAs
* ambiguous grammars allowed, yielding parse trees generated in
parallel
* LPC functions called run-time, allowing for run-time
context-sensitive pruning
Kernel Library
--------------
A kernel library is distributed along with the driver itself; this
library is written in LPC and sits as a layer between DGD and
higher-level LPC. It deals with resource control, file and object
security, and user management, and offer basic functionality in the form
of events.
* self-contained low-level LPC layer meant to constitute the
foundation of developers' own LPC systems
* restricts clonable programs to reside in /obj/ directories,
inheritables in /lib/ ; this discipline makes upgrading of inherited
programs easier
* an object ownership system
* linked lists of objects per owner
* an extensible resource control system with quotas
* a file security system
* a "thread-local storage" mechanism for data; vital for
multi-processor performance
* It guarantees a maintenance-level logon even in the event of an
emergency malfunction in other parts of the LPC library.
Availability
------------
DGD is Copyright 1993 - 2000 BeeHive Internet Technologies, Inc.
The primary distribution site for the non-commercial version of DGD is
at <<A HREF="ftp://ftp.imaginary.com/pub/LPC/servers/DGD/">ftp://ftp.imaginary.com/pub/LPC/servers/DGD/</A>>. Patches for the
experimental branch are at <<A HREF="ftp://ftp.dworkin.nl/pub/dgd/experimental/">ftp://ftp.dworkin.nl/pub/dgd/experimental/</A>>.
A commercial version of DGD is available under a license from Skotos
Tech <<A HREF="http://www.skotos.net">http://www.skotos.net</A>> -- contact <<A HREF="mailto:sales#skotos,net">mailto:sales#skotos,net</A>> for
more information. Skotos holds its commercial rights by a license from
Acuity Corporation (formerly iChat and now a wholly owned subsidiary of
Quintus Corporation).
The DGD FAQ is at <<A HREF="http://www.eyesbeyond.com/dgd/faq/faq.html">http://www.eyesbeyond.com/dgd/faq/faq.html</A>>. A DGD
mailing list is maintained by CIE and can be joined from the list's web
page at <<A HREF="http://list.imaginary.com/mailman/listinfo/dgd">http://list.imaginary.com/mailman/listinfo/dgd</A>> or
<<A HREF="mailto:dgd-request#list,imaginary.com?subject=subscribe">mailto:dgd-request#list,imaginary.com?subject=subscribe</A>>.
Archives of the mailing list for are available at
<<A HREF="ftp://ftp.dworkin.nl/pub/dgd/list-archive/">ftp://ftp.dworkin.nl/pub/dgd/list-archive/</A>>.
_______________________________________________
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</PRE>
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<ul><li>Thread context:
<BLOCKQUOTE><UL>
<LI><STRONG>Re: [MUD-Dev] Sony to ban sale of online characters from its popular gaming sites</STRONG>, <EM>(continued)</EM>
<ul compact>
<ul compact>
<ul compact>
<LI><strong><A NAME="00217" HREF="msg00217.html">Re: [MUD-Dev] Sony to ban sale of online characters from its popular gaming sites</A></strong>,
Matthew Mihaly <a href="mailto:the_logos@achaea.com">the_logos@achaea.com</a>, Wed 12 Apr 2000, 07:07 GMT
</LI>
</ul>
<LI><strong><A NAME="00199" HREF="msg00199.html">Re: [MUD-Dev] Sony to ban sale of online characters from its popular gaming sites</A></strong>,
Ryan Palacio <a href="mailto:rpalacio@verant.com">rpalacio@verant.com</a>, Wed 12 Apr 2000, 04:05 GMT
</LI>
</ul>
<LI><strong><A NAME="00194" HREF="msg00194.html">Re: [MUD-Dev] Sony to ban sale of online characters from its popular gaming sites</A></strong>,
Travis Nixon <a href="mailto:tnixon@avalanchesoftware.com">tnixon@avalanchesoftware.com</a>, Wed 12 Apr 2000, 04:03 GMT
<UL>
<LI><strong><A NAME="00242" HREF="msg00242.html">Re: [MUD-Dev] Sony to ban sale of online characters from its popular gaming sites</A></strong>,
Ryan Palacio <a href="mailto:rpalacio@verant.com">rpalacio@verant.com</a>, Fri 14 Apr 2000, 02:51 GMT
</LI>
</UL>
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</ul>
</LI>
<LI><strong><A NAME="00176" HREF="msg00176.html">[MUD-Dev] DGD Description</A></strong>,
Christopher Allen <a href="mailto:ChristopherA@Skotos.net">ChristopherA@Skotos.net</a>, Tue 11 Apr 2000, 21:26 GMT
<LI><strong><A NAME="00169" HREF="msg00169.html">[MUD-Dev] Sony to ban sale of online characters from its popular gamingsites</A></strong>,
F. Randall Farmer <a href="mailto:randy@communities.com">randy@communities.com</a>, Tue 11 Apr 2000, 18:46 GMT
<UL>
<LI><strong><A NAME="00181" HREF="msg00181.html">RE: [MUD-Dev] Sony to ban sale of online characters from its popular gamingsites</A></strong>,
Zak Jarvis <a href="mailto:zak@voidmonster.com">zak@voidmonster.com</a>, Tue 11 Apr 2000, 21:26 GMT
</LI>
<LI><strong><A NAME="00178" HREF="msg00178.html">Re: [MUD-Dev] Sony to ban sale of online characters from its popular gaming sites</A></strong>,
maddog <a href="mailto:maddog@best.com">maddog@best.com</a>, Tue 11 Apr 2000, 21:26 GMT
</LI>
</UL>
</LI>
<LI><strong><A NAME="00160" HREF="msg00160.html">[MUD-Dev] History, background and religion</A></strong>,
Pileborg Joachim - FMT <a href="mailto:joachim.pileborg@fmt.se">joachim.pileborg@fmt.se</a>, Tue 11 Apr 2000, 17:22 GMT
</LI>
</UL></BLOCKQUOTE>
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