The Missing Sync for BlackBerry
February 2009
July 2008
OS X Accessibility from Java
Our client’s application is a scriptable form-filling engine, used by their customers to automate computer-based form submission. Their engine is written in Java, and uses the Abbot GUI testing framework to drive third-party UIs. For Mac OS X support we implemented a JNI shim that made the AX API usable from Java.
January 2008
iMobimac Modem
The BlackBerry application is written in Java. It maintains a single communications channel with the Mac application, over which it receives requests to make, use and break network connections. The channel is multiplexed with ZooLib's Java ZStreamMUX on the BlackBerry side, and its C++ ZStreamMUX on the Mac.
Much of the Mac application's functionality is a C++ HTTP and port-forwarding proxy server, most of which is in ZHTTP. Its UI is implemented in Objective C using Cocoa Bindings.
The remainder of the Mac implementation effort was in reverse-engineering the BlackBerry/Host USB communications protocol.
May 2006
Knowledge Forum 4.6
Under the hood KF 4.6 has moved from using ZDBase for its backing store, instead using a tuplebase. This makes it possible to split HTML page generation into separate processes, potentially running on multiple front end machines. It also restores support for a rich client application, now written in Java, using ZTSoup to efficiently communicate changes in the tuplebase, whether made by other clients or by the web interface.
May 2004
Java Tuplebase Access
Initially I provided Java access to a tuplebase instance by implementing Java classes whose most interesting methods were marked as native, and thus invoked via JNI. This was very powerful because Java could use any tuplebase implementation simply by calling the appropriate factory function and I could expose any existing C++ functionality simply by implementing the appropriate JNI glue.
But native code can't be included with unsigned applets, so I ported ZTBRep_Client from C++ to Java. ZTBRep_Client is the most useful tuplebase implementation in that it talks to a ZTBServer instance on the end of a comms link, generally a network socket. It's also fairly large, and the async nature of the protocol makes things somewhat tricky. The normal Java synchronization model is based around monitors, which are not directly useful for implementing certain types of concurrent processing, so I implemented condition vars and mutexes to provide more appropriate tools.
October 2002
Tuplebase
ZooLib's tuplebase is derived from the tuplespace concept initially explored in the Linda coordination language, another well known derivation of which is Sun's JavaSpaces system. Whereas JavaSpaces is Java-only and relies on many of that languages's features, ZooLib's tuplebase works today with C++ and Java, and is well suited to work with other languages.
Language agnosticism is a key feature of tuplebase. Another is its runtime flexibility, which contrasts with most relational database implementations.
The power of a relational database is that the data it stores conforms to a rigorously defined structure. For a single piece of software it's always possible to find a single structure that supports all the work to be performed. As the nature of that work changes the database schema is evolved along with it. But this evolution must be coordinated so that all software that depends on the schema is updated to accommodate the changes, or virtual views are created to preserve a logical interface to the data.
Tuplebase takes a very different approach. Rather than enforcing a structure it allows any structure at all to be stored. Different pieces of software with overlapping concerns obviously must coordinate amongst themselves, but there's no requirement that there be any single authority managing everything. And because there's no mandated structure it's possible at runtime to treat multiple physical tuplebases as a single logical tuplebase, even if they contain data of different provenances. If the code using the data is written to be accommodating to the gradual migration of meaning then newer code can correctly interpret older data, and older code will ignore (but preserve) newer data.
October 2002
Tuples Defined Rigorously
For most of my career I've been very suspicious of dynamic data representations. After all, what's the point of having a compiler if it isn't provided with enough information about the shape of the data being manipulated to tell you when your code is going wrong. However, that really only works for data created and consumed within a single application. In the mid-90s, every C++ framework worth its salt had a huge bunch of code dedicated to turning arbitrary C++ objects into something that could be serialized and regenerated as objects later; and in fact that's about as far as most people got with CORBA before giving up.
But most objects in a C++ program, if they're objects at all, simply don't need to be serialized. The ones that do have disparate needs, and special cases abound. The approach I've found most flexible and least intrusive is to provide ZTuple. In this context a tuple is isomorphic to a LISP a-list, Python or Cocoa dictionary, Perl or Ruby Hash or to a Java Map. It's simply a list of name/value pairs, where values can be primitives (strings, numbers, raw bytes etc), tuples or lists of values.
ZooLib provides a suite of facilities that read and write tuples to binary streams, generate and parse a well-defined and easy to read text format, and that can read and write appropriate data formats as tuples.
December 2000
ZooLib
ZooLib abstracts threads, files, networking, graphics and the user interface. And there are escape hatches whereby OS-specific features can be accessed without compromising the platform-agnostic nature of the rest of the code.
ZooLib has been under continual development since 1992, and incorporates fixes for every OS bug or anomaly I've encountered, and generally provides cleaner mechanisms for most tasks than OSes traditionally provide. It's been the basis of Measurement in Motion, NetPhone, and every version of the Knowledge Forum server and client applications.
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