[fpc-devel] Rather large flaw in TJSONConfig component

[Graeme Geldenhuys]

Hi,

Attached is a patch which extents the jsonconf test suite. The new test
highlights a rather big flaw in the workings of the TJSONConfig component.
This issue might even apply to TXMLConfig component too - I haven't looked yet.

This came about in the discussion in the Lazarus mailing list about Lazarus
IDE storing application settings in XML files. I investigated the idea of
replacing my usage of INI files for storing application settings with JSON
files (TJSONConfig) instead. In each of my applications, I store all GUI
Form state (position, size, etc) all in one "application settings" file -
each form has it's own XXXFormState section.

In the test TestConcurrency I simulate two forms being opened - each form
contains a TJSONConfig component. When I close one form it writes the state
information. When I close the second form, it overwrites the whole JSON
file, wiping out the first form's information completely. This is rather
dangerous behaviour!

I see 3 solutions here:

1) Use a Singleton with TJSONConfig so we only have one instance of
   TJSONConfig per application.
2) Extend TJSONConfig so that it is more intelligent when writing to
   a file, and only writes the path information it modified or created.
3) When using one TJSONConfig per form, force the developer to use
   a different .json file for each form.


Any comments or alternative solutions?  I know XMLConfig and JSONConfig are
not documented yet, but if nothing is going to be done about this
concurrency issue I highlighted, then the documentation must clearly state
the dangerous behaviour of these components.


Regards,
  - Graeme -

-- 
fpGUI Toolkit - a cross-platform GUI toolkit using Free Pascal
http://opensoft.homeip.net/fpgui/

-------------- next part --------------
A non-text attachment was scrubbed...
Name: jsonconftest.patch
Type: application/mbox
Size: 1405 bytes
Desc: not available
URL: <http://lists.freepascal.org/pipermail/fpc-devel/attachments/20100621/e027c29b/attachment.mbox>