extragear/multimedia/amarok

[Thomas Braxton]

On Thursday 06 July 2006 22:32, Seb Ruiz wrote:
> SVN commit 559335 by seb:
>
> Docs on the correct usage of amaroK::config()
> CCMAIL: amarok at kde.org
>
>
>  M  +50 -0     HACKING
>
>
> --- trunk/extragear/multimedia/amarok/HACKING #559334:559335
> @@ -191,6 +191,56 @@
>      functions and to prevent problems in the future.
>
>
> +Usage of amaroK::config()
> +-------------------------
> +We provide this method for convenience, but it is important to use it
> properly. By +inspection, we can see that we may produce very obscure bugs
> in the wrong case: +
> + | KConfig *config( const QString &group )
> + | {
> + |    //Slightly more useful config() that allows setting the group
> simultaneously + |    kapp->config()->setGroup( group );
> + |    return kapp->config();
> + | }
> +
> +Take the following example:
> +
> + | f1()
> + | {
> + |    KConfig *config = amaroK::config( "Group 1" );
> + |    config->writeEntry( "Group 1 Variable", true );
> + | }
> + |
> + | f2()
> + | {
> + |    KConfig *config = amaroK::config( "Group 2" );
> + |    config->writeEntry( "Group 2 Variable", true );
> + | }
> + |
> + | doStuff()
> + | {
> + |    newThread( f1() );
> + |    newThread( f2() );
> + | }
> +
> +We would expect the following results:
> +
> + | [Group 1]
> + | Group 1 Variable = true
> + |
> + | [Group 2]
> + | Group 2 Variable = true
> +
> +However, it is possible, due to threads, that the config group is changed
> before writing the entry: + | [Group 1]
> + |
> + | [Group 2]
> + | Group 1 Variable = true
> + | Group 2 Variable = true
> +
> +Which is clearly incorrect.
> +
> +
>  Errors & Asserts
>  ----------------
>  *Never use assert() or fatal(). There must be a better option than
> crashing a user's
Why not just use KConfigGroup? This would allow you to be thread safe, since 
all readEntry/writeEntry calls are passed to the correct group. And the base 
object's group is never changed, so you don't have to worry about what other 
threads are saving.

Instead of writing
amaroK::config("PlaylistBrowser")->readNumEntry("Sorting", Qt::Ascending);
... other stuff that uses amaroK::config ...

write
KConfigGroup config(app->config(), "PlaylistBrowser");

config.readNumEntry("Sorting", Qt::Ascending);
... other stuff that uses config ...