Subject Enhancement Suggestion: Client Libraries
Author Geoff Worboys
Hi All - but in particular Jason,

I am fiddling around with a project, I wont bother you with
the details but the upshot is that I would really like to be
able to specify the Firebird client library at startup
according to a command line parameter (or perhaps a registry

That is to say; I want to be able to choose library "x" in
some situations and library "y" in others - without having to
recompile the application.

The problem with the current code is that the IB_Session proc
"ReserveSessionHookRef" is called from various initialization
sections (IB_Session and IB_Monitor - and indirectly from
any IB_Component that is created during initialisation).

Initialization sections are called before we get into the
the program itself, which prevents runtime customisation (or
at least prevents it from being easy and predictable).

I am guessing that some of the work in ReserveSessionHookRef
MUST be called during initialisation - the critical section
stuff. However that procedure also calls "AcquireOriginalHooks"
which is where the library gets opened and the library function
hooks get acquired.

I did the following test with IB_SQL: I renamed the FB library
so it could not be found and started IB_SQL. It started with
no complaints - so obviously the function hooks were not
essential at that point (more about this aspect in a moment).
I then left IB_SQL running and renamed the client library back
again and tried to establish a connection. It worked! The
TIB_Connection actually checks whether the hooks are acquired,
and calls AcquireOriginalHooks if it needs to do so.

So... for "normal" situations there appears to be no need to
acquire the library hooks until we are ready to actually make
a connection. We could remove the early (initialization)
opening of the library, which would then allow a program to
start up and specify what library file it wanted (in a global
variable or by defining a global function), and normal access
would be able to proceed without other changes.

With appropriate changes it could even be possible to unload
the FB client library at runtime and (optionally) specify a
different library for the next task.

I have identified some situations that can cause problems...

Starting IB_Monitor before establishing a connection

Calling GetISC4Path or CreateDatabase (these call the API
hooks without checking if they have been initialised)

There also appear to be issues in IB_Connection from alternate
threads - I suspect the hook pointers just need initialising
to nil in IB_Session.

Can anyone think of other potential problems of not initialising
the library hooks until a connection is made?

Given the limited number of "problem" situations we should be
able to explicitly deal with those in some appropriate way.

Any other thoughts on this topic?

Jason, perhaps you have other plans for tackling this issue.
I seem to remember we discussed it some time ago, but I do not
remember what we decided.

Geoff Worboys
Telesis Computing