> On Sep 11, 2017, at 09:54, Elvis Stansvik <[email protected]> wrote: > > 2017-09-11 9:33 GMT+02:00 Eike Ziller <[email protected]>: >> >>> On Sep 10, 2017, at 13:09, Elvis Stansvik <[email protected]> wrote: >>> >>> Right, the two-phase plugin initialization and object pool is quite >>> well described in the docs: >>> >>> https://doc-snapshots.qt.io/qtcreator-extending/plugin-lifecycle.html >>> >>> I think my question was a little vague, sorry about that. >>> >>> Consider an example: Some functionality "foo" is to be added to the >>> core plugin, and a plugin Bar written to implement that functionality. >>> >>> Approach 1: >>> >>> - Add an interface IFoo to the core plugin. >>> - Bar implements IFoo and add an instance of its implementation to the >>> pool in its initialize(). >>> - The core plugin get the object from the pool (in its >>> extensionsInitialized()), and make use of it. >>> >>> Approach 2: >>> >>> - Add a singleton Foo to the core plugin. >>> - Bar carries out its work using direct calls on Foo::instance(). >>> >>> I was just wondering if the second approach is ever used, or if the >>> mechanism set up by the object pool + two-phase initialization is >>> always used. If approach 2 is used, I was interested in what the >>> deciding factor is between the two approaches. >> >> Many good things have already been said, I’m late :) > > You're very welcome any time Eike :) > >> >> Basically there is also >> >> Approach 3: >> >> - Add an interface IFoo to the core plugin >> - Add a static method for registering instances of IFoo to core plugin >> - Bar implements IFoo and registers an instance of its implementation via >> the method above >> - The core plugin gets the object(s) that have been registered through the >> static method (in its extensionsInitialized or later) > > Ah yes of course. > >> >> Approach 1 works when there should not be a hard runtime dependency between >> the plugins (at compile time the interface header is needed). For making >> this work without a link dependency, the interface must use >> Q_DECLARE_INTERFACE. I think the only place where it actually used this way >> is with CodePaster::Service, to avoid a runtime dependency between >> CodePaster and DiffEditor plugins. Historically we used that a lot also when >> there actually already was a hard runtime dependency between the plugins, >> which is problematic because of the performance issue that André hinted at. > > Aha, I was actually going to ask if plugin dependencies (as declared > in their metadata) always implies a link time dependency as well, > because when I looked at qtcreator.pri (the loops at the bottom that > add to LIBS), it looked to me like it does. But you're saying that if > Q_DECLARE_INTERFACE is used in the depended-upon plugin's interface > class, then there will be no link time dependency introduced, despite > -l<dep> being always being added to the link line for the depending > plugin?
To avoid an actual link time dependency, the dependency has to also be declared as “optional”, i.e. QTC_PLUGIN_RECOMMENDS instead of QTC_PLUGIN_DEPENDS Br, Eike > >> >> In Approach 2 we actually moved towards using mostly classes with static >> methods, only using the instance() when we actually need an instance (e.g. >> for connecting to signals). It works well when a hard runtime dependency is >> ok and Bar is the driving force for the work to be done. I would say that we >> do this a lot, e.g. ActionManager, EditorManager, …, but I don’t know if you >> meant that kind of interaction ;) > > Yes, my description of 2 was a bit vague, but this was what I meant I think. > > Having static methods that delegate to the instance() does make the > calls more readable, so I like that. > >> >> Approach 3 works well if a hard runtime dependency between the plugins is >> ok. We still experiment with ways for avoiding the monotonous work of adding >> add/registerXXX, remove/unregisterXXX, methods for managing the list of >> implementations. One experiment is Utils::ObjectPool. One could add a public >> static instance of that to the core plugin in your example, and then call >> Core::foos.addObject(myIFooImpl) from Bar plugin. > > Ah, I hadn't seen that one. That makes sense. I see that it also > defaults to destroying the objects when the pool destructs, which > makes sense since looking at the number of IPlugin::addObject calls vs > IPlugin::addAutoReleasedObject, it looks like most of the time you > want the auto-destruction behavior. > >> >> I’d also prefer having fewer hard runtime dependencies, but it is a >> struggle… Qt helps a bit, but it is still not nice. >> There is the Q_DECLARE_INTERFACE/Q_INTERFACES combo + object pool, there is >> invokeMethod + object pool, and the other thing that we also use is custom >> QObject properties (e.g. CodePaster looks for a custom property “plainText” >> in the current IEditor, as a fallback for finding pasteable text). > > Alright, thanks for the insight! > > Elvis > >> >> Br, Eike -- Eike Ziller Principal Software Engineer The Qt Company GmbH Rudower Chaussee 13 D-12489 Berlin [email protected] http://qt.io Geschäftsführer: Mika Pälsi, Juha Varelius, Mika Harjuaho Sitz der Gesellschaft: Berlin, Registergericht: Amtsgericht Charlottenburg, HRB 144331 B _______________________________________________ Qt-creator mailing list [email protected] http://lists.qt-project.org/mailman/listinfo/qt-creator
