From IBOBjects FAQ
Is there a way to detect a lost connection and try to reconnect
automatically, without user action?
Hook into the OnError event and look for the ERRCODE that denotes a
lost connection. Then, you can take whatever action you deem necessary
to deal with the problem. If the connection is lost you need to do a
disconnect and then connect again.
And from one of the base members of the IBObjects:
However, perhaps the "something" you are missing is that, if the
connection is broken by an external cause, the client application has
no way to know that it is not still connected. Its first knowledge of
that fact will come the next time it tries to access the server. The
API will report "Connection lost to database" and return GDSCODE
335544741, which is identified by the constant
isc_lost_db_connection.
At the point where this exception occurs, the TIB_Connection still
thinks it is connected - the Connected property will be true. If you
try to reconnect by calling Connect, you will get an IBO exception.
It is necessary to call Disconnect. This does not simply reset a
property. The Disconnect method performs all of the necessary cleanup
to invalidate the broken transactions and cancel any now invalid
postings, datasets and caches. Once Disconnect has completed its
work, you can then place a Connect call inside a retry loop and
attempt to get going again.
I do not know of a working example, but the simplest way to deal with
this is to write a RestoreConnection handler procedure that you can
call from your IB_Session.OnError handler whenever argument ERRCODE
returns isc_lost_db_connection.
Have your RestoreConnection procedure do whatever you need to do,
trying to call Connect and handling the exception that occurs if the
request fails, until no exception occurs. Test the Connected property
after each iteration. When Connected is finally True, you are in
business. You can drop out of the retry code and inform the user that
the connection has been restored - perhaps with a sound and/or a
message in the status bar, to avoid having to show a dialog box that
she has to respond to. (if you like the idea of sound and status bar
cues, you could devise "connection lost" warning sound and status bar
message code to run at the beginning of your handler procedure as
well...)
If these broken connections are a frequent occurrence, you might like
to consider making a distinctive custom cursor that you can display
while your procedure is running, and enclose the retry code in a
non-yielding BeginBusy...EndBusy block with UseCursor enabled and
BusyCursor set to use this special cursor image.
And if re-establishing a connection is likely to take a long time, or
to be temporarily impossible, you would need to provide the ability
for the user to intervene and choose not to keep trying. You can use
the session timer for this, enclosing your "busy" block inside
another iterative block the prompts the user to "Cancel" or "Keep
Trying", at reasonable intervals.
Source
