Metakit 1.8.5 does not support concurrent access to its datafile. It does support threading in a limited way. Multi-user/concurrent access is by far the most requested feature (second on the list are the requests to make Metakit even faster and/or to let it handle much larger files - see the [Performance] page).
Some facts about Metakit 1.8.5
So that's it? No concurrent use at all?
The suggested way around this, is to introduce a client/server mechanism (this can also be used inside a single multi-threaded app, btw). For C++, this might be a lot of work - but the concept is definitely not new or complex. In Tcl, a server and client each take no more than about a dozen lines of code. Such an approach will not be applicable in all cases, I am looking at several ways to provide more solutions.
August 1999, good news: a multi-threaded version of MK has been designed, which supports multiple readers and one writer - this is expected to be ready and fully tested well before the end of 1999.
April 2000, bad news: it hasn't happened. But as the New MK transaction modes page shows, there is tangible progress. It is slightly different from the original design, and it's working code.
August 2003 : Metakit Locking Class
Jeffrey Kay (mailto:[email protected]) has very kindly donated the source and an example for a c++ Metakit locking class. JCW Has kindly uploaded it to https://www.equi4.com/pub/etc/mklock.zip
From The discussion forum :- " I've solved the problem by creating a couple of "locking" classes to ensure that I don't accidentally access a store from multiple threads. The first class opens up a db file. I've designed my code so that I have only one class managing a db file, so that class is derived from shDBManager. The second class retrieves a reference to a given store and sets a critical section to ensure that only one thread is working on the store. To protect myself, I usually make shStore a stack variable. "
A further note from Jeff "I only compiled the debug version - dependencies are to ../../metakit-2.4.7. The code works fine with 2.9.2 or whatever the most recent MK version is - I just didn't happen to have it on the system that I'm sitting at right now."
Many thanks Jeff for being such a good sport.
If people wish to see another way of doing it, please also see John Taylor's work 'openrepo' (repository), from www.shift-right.com .... Ex John : "If anyone is interested. In the course of using Metakit in our products at work, we have created a Multi-threaded C++ wrapper for Metakit. It is a client/server model using ITC (inter-thread-communications) to isolate all database actions for a given a database to a single thread. The wrapper is part of my company's open source C++ library."
I hope putting such articles together here in one place helps.
cheers, Garth