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GNU Objective-C Class Library README
************************************
Here is some introductory info to get you started:
Initial reading
===============
The file `ANNOUNCE' contains a very brief overview of the library.
It also tells you where to get the most recent version.
The file `NEWS' has the library's feature history.
The file `INSTALL' gives instructions for installing the library.
The file `DISCUSSION' contains the archives of email discussions
about the library. It's a good place to read about the reasons for
some of the design decisions.
Preparing to write code
=======================
The documentation isn't much to speak of so far. Better
documentation will be forthcoming, but the library needs to settle
first. For now I recommend skipping libobjects.info and reading the
header files instead. The headers for the GNU classes are in
./objects; the headers for the NeXT-compatible classes are in
./objects/next-include.
[NOTE: To compile code that uses NeXT compatibility classes, you'll
want to put `XX/objects/next-include' in your include file search path.
Then, (unlike with the old libcoll), you can use #include <objc/List.h>
instead of #include <coll/List.h>.]
The overview of classes below should help you see the big picture as
you read the source.
The Class Heirarchy
===================
Here is the class inheritance heirarchy. All protocols end with
"ing"; all collection protocols end with "Collecting". All collection
abtract superclasses (classes which are not usable without subclassing)
end with "Collection";
Collection <Collecting>
Set
Bag
KeyedCollection <KeyedCollecting>
Dictionary
MappedCollector
IndexedCollection <IndexedCollecting>
Array
Stack
GapArray
CircularArray
Queue
Heap
LinkedList
BinaryTree
RBTree
EltNodeCollector
String
DelegatePool
LinkedListNode
LinkedListEltNode
BinaryTreeNode
BinaryTreeEltNode
RBTreeNode
RBTreeEltNode
Stream
StdioStream
MemoryStream
Coder
TextCoder
BinaryCoder
ConnectedCoder
Port <Coding>
SocketPort
Connection
Proxy <Coding>
Magnitude
Time
Random
RNGBerkeley <RandomGenerating>
RNGAdditiveCongruential <RandomGenerating>
Overview of the classes
=======================
The GNU classes included in this version of the library fall into
five categories: collections, magnitudes, streams, coders and
distributed object support.
* The collection objects all conform to the `Collecting' protocol.
Reading `./objects/Collecting.h' is a good place to start.
Protocols for collections that store their contents with keys and
with indices can be found in `./objects/KeyedCollecting.h' and
`./objects/IndexedCollecting.h' respectively. Examples of generic
collections are `Set' and `Bag'. The keyed collections are
`Dictionary' and `MappedCollector'. The classes `Array', `Queue',
`GapArray', `LinkedList', `BinaryTree', `RBTree' and `SplayTree'
are all indexed collections.
* The public magnitude classes are `Time' and `Random'. The
`Random' class works in conjunction with pseudo-random number
generators that conform to the `RandomGenerating' protocol. The
conforming class `RNGBerkeley' provides identical behavior to the
BSD random() function. The class `RNGAdditiveCongruential' is an
implementation of the additive congruential method.
* Stream objects provide a consistent interface for reading and
writing bytes. Read `./objects/Stream.h' to get the general idea.
`StdioStream' objects work with files, file descriptors, FILE
pointers and pipes to/from executables. `MemoryStream' objects
work with memory buffers.
* Coders provide a formatted way of writing to Streams. After a
coder is initialized with a stream, the coder can encode/decode
Objective C objects and C types in an architecture-independent
way. See `./objects/Coder.h' for the abstract superclass
interface; see `./objects/Coding.h' for the protocol adopted by
objects that read and write themselves using coders. The
currently available concrete coder classes are `BinaryCoder', for
reading and writing a compact stream of illegible bytes, and
`TextCoder', for reading and writing human-readable text (which
you can also process with `perl', `awk', or whatever scripting
language you like).
Coders and streams can be mixed and matched so that programmers can
choose the destination and the format separately.
Neither the stream or coder class heirarchies are very mature yet.
I threw them together because I needed them for distributed
objects.
* The distributed object support classes are `Connection', `Proxy',
`ConnectedCoder', `Port' and `SocketPort'. This version of the
distributed objects only works with sockets. A Mach port back-end
should be on the way.
[NOTE: The GNU distributed object facilities have the same
ease-of-use as NeXT's; be warned, however, that they are not
compatible with each other. They have different class
heirarchies, different instance variables, different method names,
different implementation strategies and different network message
formats. You cannot communicate with a NeXT NXConnection using a
GNU Connection. The GNU distributed object code does not work
with the NeXT Objective C runtime. NXConnection creates NXProxy
objects for local objects as well as remote objects; GNU
Connection doesn't need and doesn't create proxies for local
objects. NXProxy asks it's remote target for the method encoding
types and caches the results; GNU Proxy gets the types directly
from the local GNU "typed selector" mechanism and has no need for
querying the remote target or caching encoding types. The NXProxy
for the remote root object always has name 0 and, once set, you
cannot change the root object of a NXConnection; the GNU Proxy for
the remote root object has a target address value just like all
other Proxy's, and you can change the root object as many times as
you like. See the "lacking-capabilities" list below for a partial
list of things that NXConnection can do that GNU Connection
cannot.]
To begin using distributed objects, you only need to know about
`Connection' class. You can see the full interface in
`./objects/Connection.h'. The long list of methods may be a little
daunting, but actually, a lot can be done with just a few key
methods:
- (Connection*) newRegisteringAtName: (const char*)name
withRootObject: anObj;
For registering your server object with the network.
- (void) runConnection;
For running the connection object returned by the above
method, so that your server can start handling requests from
clients.
- (Proxy*) rootProxyAtName: (const char*)name
onHost: (const char*)host;
For connecting to a remote server. You get a proxy object for
the remote server object, which, for messaging purposes, you
can treat as if it were local.
Here is a partial list of what the current distributed objects
system can do:
- It can pass and return all simple C types, including char*, float
and double, both by value and by reference.
- It can pass structures by value and by reference, return
structures by reference. The structures can contain arrays.
- It obeys all the type qualifiers: oneway, in, out, inout, const.
- It can pass and return objects, either bycopy or with proxies.
An object encoded multiple times in a single message is properly
decoded on the other side.
- Proxies to remote objects are automatically created as they are
returned. Proxies passed back where they came from are decoded
as the correct local object.
- It can wait for an incoming message and timeout after a
specified period.
- A server can handle multiple clients.
- The server will ask its delegate before making new connections.
- The server can make call-back requests of the client, and keep
it all straight even when the server has multiple clients.
- A client will automatically form a connection to another client
if an object from the other client is vended to it. (i.e. Always
make a direct connection rather than forwarding messages twice,
once into the server, from there out to the other client.)
- The server will clean up its connection to a client if the client
says goodbye (i.e. if the client connection is freed).
- When the connection is being freed it will send a invalidation
notification message to those objects that have registered for
such notification.
- Servers and clients can be on different machines of different
architectures; byte-order and all other architecture-dependent
nits are taken care of for you. You can have SPARC, i386, m68k,
and MIPS machines all distributed-object'ing away together in
one big web of client-server connections!
Here is a partial list of what the current distributed objects
system does *not* do:
- Run multi-threaded.
- Detect port deaths (due to remote application crash, for example)
and do something graceful.
- Send exceptions in the server back to the client.
- Send messages with vararg arguments.
- Return structures by value.
- Use Mach ports, pass Mach ports, pass Mach virtual memory.
- Send messages more reliably than UDP. It does detect reply
timeouts and message-out-of-order conditions, but it's reaction
is simply to abort.
- Claim to be thoroughly tested.
Where else to look
==================
Examples
--------
A few simple example programs can be found in `./examples'. Read
and enjoy. To compile them (after having compiled the library), type
`make' in the `examples' directory.
* `dictionary.m' demonstrates the basic features of the Dictionary
object.
* `stdio-stream.m' creates a StdioStream object that points to a
file, writes to the file, then reads from the file.
* `textcoding.m' shows how you can archive an object to a file in a
human-readable text format, and then read it back in again. This
format is handy for editing archived objects with a text editor,
and is great when you want to modify/create an archive using a
scripting language like `perl' or `awk'.
* `first-server.m' and `first-client.m' show the distributed object
version of "Hello, world".
* `second-server.m' and `second-client.m' contain a more complex
demonstration of distributed objects, with multiple clients,
connection delegates, and invalidation notification.
* `port-server.m' and `port-client.m' show a simple use of Port
objects. Be warned, however, the interface to Port objects will
likely change in the near future.
Test Programs
-------------
Some of the programs I've used to test the library are in
`./checks'. Many of them are pretty messy, (desperately trying to
tickle that late night bug), but at least they show some code that works
when the library compiles correctly. I'm looking for a volunteer to
write some nicely organized test cases using `dejagnu'. Any takers?
Coming Soon...
==============
More improvements to the library are on the way. Closest in the
pipeline are String objects and better allocation/deallocation
conventions for objects.
These improvements will bring some changes to the current interfaces:
(1) Almost everywhere that the current methods now take (char*)
arguments, the new methods will take (String*) arguments. (2) The use
of the method `free' will be abolished and replaced by new methods.
I'm trying to get these changes in place as soon as possible so that
you don't end up writing too much code that uses the old (i.e. current)
interfaces.
Meanwhile, please use the library! The small amount of changes you
may need to make won't be difficult, and the earlier I get usability
suggestions and bug reports, the sooner the fixes will come.
How can you help?
=================
* Read the projects and questions in the `TODO' file. If you have
any useful comments mail them to me!
* Give me feedback! Tell me what you like; tell me what you think
could be better. Send me bug reports.
* Donate classes. If you write classes that fit in the libobjects
framework, I'd be happy to include them.
Happy hacking!
Andrew McCallum
mccallum@gnu.ai.mit.edu
These are the contents of the former NiCE NeXT User Group NeXTSTEP/OpenStep software archive, currently hosted by Netfuture.ch.