...because this topic serves as a vehicle to elaborate various core concepts
of the UI backbone, especially how to access, bind and invoke Proc-Layer commands
...turns out to be a nasty subject, now we're able to see
in more concrete detail how this interaction needs to be carried out.
Basically this is a blocker for the top-level, since it is obviously
some service in top-level, which ultimately becomes responsible for
orchestrating this activity
this pretty much resolves most of the uncertainities:
we now get a set of mutually dependent services, each of which
is aware of each other member's capabilities, but accesses those
only through this partner's API
After quite some pondering, it occured to me that we both
- need some top-level model::Tangible to correspond to the RootMO in the session
- need some Controller to handle globally relevant actions
- need a way to link action invocation to transient interaction state (like focus)
This leads to the introduction of a new top-level controller, which is better
suited to fill that role than the depreacted model-controller or the demoted window-manager
looks like we're in management business here ;-)
we chop off heads, slaughter the holy cows and then install -- a new manager
...allows us to get rid of a lot of sigc boilerplate syntax.
The downside is that the resulting functors are not sigc::trackable.
This seems adequate here, since the whole top-level UI backbone is
maintained by GtkLumiera, and thus ensured to exist as long as the
main GTK event loop is running.
WARNING: beware of creating "wild" background thrads in the UI, without
proper scheduling of any communication via the event loop!
This is a very pervasive change and basically turns the whole top-level
of the GTK-UI bottom-up. If this change turns out right, it would likely
solve #1048
WARNING: in parts not implemented, breaks UI
...which itself is obsolete and needs to be redesigned from scratch.
For now we create a local instance of this obsolete PlaybackController
in each viewer panel and we use a static accessor function to just some
instance. Which would break if we start playback with multiple viewer
panels. But we can't anyway, since the Player itself is also a broken
leftover from an obsoleted design study from the early days.
so why care...
- WindowList (ex WindowManager)
- Project & Controller
the latter ones are defunct and can be replicated down into each
of the old timeline pannel instances. They just serve the purpose
to keep this old code barely functional, so it can be used as reference
for building the new timeline
There seems to be a mismatch in the arrangement of the top-level entities
* we support multiple windows, yet from reading the code, you'd ge the impression we aren't really aware we have multiple top-level windows
* the `WindowManager` is the core UI manager, which feels like a mix-up in concerns
* the `WorkspaceWindow::createUI()` does the global UI initialisation. Again, we have multiple workspace windows.
* `GtkLumiera::main()` creates a `Model` and a `Controller` in local function scope, but stores the `WindowManager` in an object field.
* it seems, for that very reason, `GtlLumiera` needed to be a singleton, to allow by-name access to "the" `WindowManager`
* needless to say, this causes a host of problems when shutting down the UI.
The idea is to introduce a dedicated UiManager, to deal with the central
framework induced concerns solely, and to demote the WindowManager and the
WorkspaceWindows to care only for their local concerns
in fact it just does not fulfil any of the behavioural properties
of a full-fledged UI-Element. All it needs is an uplink bus connection,
so let's just keep it as that
Sidenote: I've realised today that such a "free standing" BusTerm
without registration in Nexus is a good idea and acceptable solution.
yes, it's a cycle and indeed quite tricky.
Just verified it (again) with the debugger and saw all
dtor calls happening in the expected order. Also the number
of Nexus registration is sane
Now I've realised that there are two degrees of connectedness.
It is very much possible to have a "free standing" BusTerm, which
only allows to send uplink messages. In fact, this is how CoreService
is implemented, and probably it should also the way how to connect
the GuiNotification service...
Reason was some insideous detail regarding Lambdas:
When a Lambda captures context, a *closure* is created.
And while the Lambda itself is generated code, pretty much
like an anonymous function, the closure depends on the context
that was captured. In our case here, the Lambda used to start
the thread was the problem: it captured the termCallback functor
from the argument of the enclosing function. In fact it did not
help or change anything if we successively package that lambda
into a function objet and store this by value, because the
lambda still refers to the transient function context present
on stack at the moment it was captured.
The solution is to revert back to a bind expression, since this
creates a dedicated storage for the bound function arguments
managed within the bind-functor. This makes us independent
from the call context
...because some Bus connections stem from elements which are
member of CoreService, thus the'll still be connected when the
sanity check in the dtor runs
But even with this fix, we still get a SEGFAULT
TODO
- is this actually a sensible idea, from a design viewpoint?
- in which way to bind GuiNotification for receiving diff messages?
- Problem with disconnnecting from Nexus on shutdown
Writing and debugging such tests is always an interesting challenge...
Fortunately this exercise didn't unveil any problem in the newly written
code, only some insidious problems in the test fixture itself. Which
again highlights the necessity, that each *command instance* needs
to be an independent clone from the original *command prototype*,
since argument binding messages and trigger messages can appear
in arbitrary order.
not quite sure how to get the design straight.
Also a bit concerned because we'll get this much indirections;
the approach to send invocations via the UI-Bus needs to prove its viability
Did a full review of state and locking logic, seems airtight now.
- command processing itself is unimplemented, we log a TODO message for now
- likewise, builder is not implemented
- need to add the deadlock safeguard #1054
We found out that it's best to run it single threaded
within the session loop thread. This does not mean the Builder
itself is necessarily single threaded, but the Builder's top level
will block any other session operation, and this is a good thing.
For this reason it makes more sense to have the Builder integrated
as a component into the session subsystem.
after reading some related code, I am leaning towards a design
to mirror the way command messages are sent over the UI-Bus.
Unfortunately this pretty much abandons the possibility to
invoke these operations from a client written in C or any
other hand made language binding. Which pretty much confirms
my initial reservation towards such an excessively open
and generic interface system.
...this means to turn Looper into a state machine.
Yet it seems more feasible, since the DispatcherLoop has a nice
checkpoint after each iteration through the while loop, and we'd
keep that whole builder-dirty business completely confined within
the Looper (with a little help of the DispatcherLoop)
Let's see if the state transition logic can actually be implemented
based just on such a checkpoint....?
....if by some weird coincidence, a command dispatched into the session
happens to trigger session shutdown or re-loading, this will cause a deadlock,
since decommissioning of session data structures must wait for the
ProcDispatcher to disable command processing -- and this will obviously
never happen when in a callstack below some command execution!
After some consideration, it became clear that this service implementation
is closely tied to the DispatcherLoop -- which will consequently be
responsible to run and expose this service implementation
need to keep state variables on both levels,
since the session manager (lifecycle) "opens" the session
for external access by starting the dispatcher; it may well happen
thus that the session starts up, while the *session subsystem*
is not(yet) started
mark TODOs in code to make that happen.
Actually, it is not hard to do so, it just requires to combine
all the existing building blocks. When this is done, we can define
the "Session" subsystem as prerequisite for "GUI" in main.cpp
Unless I've made some (copy-n-paste) mistake with defining the facades,
this should be sufficient to pull up "the Session" and automatically
let the Gui-Plugin connect against the SessionCommandService
up to now this happened from the GuiRunner, which was a rather bad idea
- it can throw and thus interfer with the startup process
- the GuiNotification can not sensibly be *implemented* just backed
by the GuiRunner. While CoreService offers access to the necessary
implementation facilities to do so
so the true reason is an inner contradiction in the design
- I want it to be completely self similar
- but the connection to CoreService does not conform
- and I do not want to hard code CoreService into the Nexus classdefinition
So we treat CoreService as uplink für Nexus and Nexus as uplink for CoreService,
with the obvious consequences that we're f**ed at init and shutdown.
And since I want to retain the overall design, I resort to implement
a short circuit detector, which suppresses circular deregistration calls
Decision was made to use the CoreService as PImpl to organise
all those technical aspects of running the backbone. Thus,
the Nexus (UI-Bus hub) becomes part of CoreService
...problem is, I actually don't know much about what kinds of markers
we'll get, and how we handle them. Thus introducing a marker kind
is just a wild guess, in order to get *any* tangible attribute
this is a tricky problem and a tough decision.
After quite some pondering I choose to enforce mandatory fields
through the ctor, and not to allow myself cheating my way around it
it occurred to me that effectively we abandoned the use of
a business facade and proxy model in the UI. The connection
becomes entirely message based now.
To put that into context, the originally intended architecture
never came to life. The UI development stalled before this could
happen; possibly it was also hampered by the "impedance mismatch"
between our intentions in the core and such a classical, model centric
architecture. Joel several times complained that he felt blocked; but
I did not really understand this issue. Only recently, when I came to
adapting the timeline display to GTK-3, I realised the model centric
approach can not possibly work with such an open model as intended
in our case. It would lead to endless cascades of introspection.
these are just empty class files, but writing a basic description
for each made me flesh out a lot of organisational aspects of what
I am about to build now
...it seemed first that we'd might run into a very fundamental problem;
but after some consideration it turns out the interspersed display manager
and the decoupling between model/presenter and widget happens to mitigate
this problem as well.
