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Jeroen W. Pluimers on .NET, C#, Delphi, databases, and personal interests

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Archive for August 10th, 2009

Delphi – Using FastMM4 part 2: TDataModule descendants exposing interfaces, or the introduction of a TInterfacedDataModule

Posted by jpluimers on 2009/08/10

This is the second post of a series of posts around using FastMM4.
The start of the series contains a listing of other posts as well and will be updated when new posts become available.

One of the larger projects I’ve becoming involved in, uses a pattern that uses TDataModule descendants exposing interfaces.
Interfaces in Delphi are nice: if used properly, you have reference counting that will automatically free the underlying objects if there are no references left to them.

When you do not do interfaces in Delphi properly, you are bound to have a lot of memory leaks, and this is one of the cases where we did.
The client choose to do testing and QA very late in the product cycle, and we choose to use FastMM to do memory debugging.
Lo and behold: a truckload of memory leaks appeared all having to do with those datamodules.

As a side node:
Another thing we bumped into at an earlier stage was lifetime management in general: (both interface and object) references were kept to objects long after they were disposed.
That caused a lot of EAccessViolation
It is best not to mix the “interface reference” pattern with the “owned component” pattern: you usually end up with many more EAccessViolation exceptions.

This article is about finding the memory leaks caused by the way the interfaces were exposed from the TDataModule descendants, and a solution for preventing them by introducing the concept of TInterfacedDataModule.
Read the rest of this entry »

Posted in Conference Topics, Conferences, Database Development, Debugging, Delphi, Development, Event, FastMM, Software Development | 10 Comments »

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