This is the first step towards a »Test Domain Ongology« #1372,
which is a systematic arrangement of test-dummy functionality assumed
to mirror the actual media processing functionality present in external libs.
Each media-processing library not only provides functions to crunch data,
but also establishes a framework of entities and classification to determine
what »media« is an how it is structured and can be generated, transformed
and qualified. Since a essential goal for Lumiera is to be **library agnostic,**
it is important to avoid naïvely to take some popular library's choices
as universal truth regarding structure and nature of »media« as such.
Rather, the architecture of the Lumiera Render Engine must be kept
sufficiently open to accommodate the working style of various libraries,
even ones not known today.
To validate this architectural openness, we use a set of test functions
unrelated to any existing library to validate access to and usage of
rendering functionality — followed by further steps to adopt existing
popular libraries like **FFmpeg** or **Gstreamer**, without tilting
the basic structure of the Render Engine one way or the other.
showing the Node-symbol and a reduced rendering of
either the predecessor or a collection of source nodes.
For this we need functionality to traverse the node graph depth-first
and collect all leaf nodes (which are the source nodes without predecessor);
such can be implemented with the help of the expandAll() functionality
of `lib::IterExplorer`. In addition we need to collect, sort and deduplicate
all the source-node specs; since this is a common requirement, a new
convenience builder was added to `lib::IterExplorer`
...taking into account the prospecive usage context
where the builder expressions will be invoked from within
a media-library plug-in, using std::string_view to pass
the symbolic information seems like a good fit, because
the given spec will typically be assembled from some
building blocks, and thus in itself not be literal data.
Building a precise Frame Cache is a tough job, and is doomed to fail
when attempting to tie cache invalidation to state changes. The only
viable path is to create a system of systematic tagging of processing
steps, and use this as foundation for chained hash values, linked
in accordance to the actual processing structure.
This is complicated by the secondary concern of maintaining memory efficacy
for the render node model, which can be expected to grow to massive scale.
And even while this invocation can not be fully devised right now,
an attempt can be made to build a foundation that is not outright
wasteful, by detaching the logical information from the specific
weaving pattern used for implementation, and by minimising the
representation in memory and computing the compound information
on-demand....
The immediate next goal is to verify properties of render nodes
generated by the builder framework; two kinds of validations
can be distinguished
* structural aspects of the wiring
* the fact that processing functionality is invoked in proper order
Looking into the structural aspects brings about the necessity
to identify the actual processing function bound into some functor.
Some recapitulation of goals and requirements revealed, that this
can not be a merely technical identity record — because the intention
is to base the ''cache key'' on chained processing node identities,
so that the key is stable as long as the user-visible results will be
equivalent. And while structural data can be aggregated, at the
core this information must be provided by the scheme embedded
into the domain ontology, which is tasked with invoking the
builder in order to implement a ''specific processing-asset''
Review the achievements from the last days and map out the further path
for test-driven build-up of a render-node network and invocation.
Notably ''several layers of prototyping'' are in the works now;
it is important to understand the purpose of each such round of
prototyping and to draw the necessary conclusions after closing out.
The next topic to investigate relates to the ''identity'' of nodes and
ports within nodes; this entails to generate a ''symbolic spec'' that
can be verified and used as base for a systematic hash-ID and cache-key...
Since it would in fact be possible to access and write beyond the configured storage,
simply by using the builder API without considering consistency,
it seems advisable to use explicit runtime checks here, instead of
only assertions, and to throw an exception when violating bounds.
Moreover, unsuccessfully attempted to better arrange the functionality
between PortBuilder and WeavingBuilder; seemingly we have an rather tight
coupling here, and also the expectations regarding the processing function
seem to be too tight (but that's the reason why it's an prototype...)
- the chaining constructor is picked reliably when the
slicing is done by a direct static_cast
- the function definition can be passed reliably in all cases
after it has been ''decayed,'' which is done here simply by
taking it by-value. This is adequate, since the function
definition must be copied / inlined for each invocation.
With these fixes, the simplest test case now for the first time
**runs through without failure**
This change allows to disentangle the usages of `lib::SeveralBuilder`,
so that at any time during the build process only a single instance is
actively populated, all in one row — and thus the required storage can
either be pre-allocated, or dynamically extended and shrinked (when
filling elements into the last `SeveralBuilder` currently activated)
By packaging into a λ-closure, the building of the actual `Port`
implementation objects (≙ `Turnout` instances) is delayed until the
very end of the build process, and then unloaded into yet another
`lib::Several` in one strike. Temporarily, those building functor
objects are „hidden“ in the current stack frame, as a new `NodeBuilder`
instance is dropped off with an adapted type parameter (embedding the
λ-type produced by the last nested `PortBuilder` invocation, while
inheriting from previous ones.
However, defining a special constructor to cause this »chaining«
poses some challenge (regarding overload resolution). Moreover,
since the actual processing function shall be embedded directly
(as opposed to wrapping it into a `std::function`), further problems
can arise when this function is given as a ''function reference''
...and as expected, this turns up quite some inconsistencies,
especially regarding usage of the »buffer types«.
Basically, the `PortBuilder` is responsible for the high-level functionality
and thus must ensure the nested `WiringBuilder` is addressed and parameterised
properly to connect all »slots« of the processing function.
- can use a helper function in the WiringBuilder to fill in connections
- but the actual buffer types passed over these connectinos are totally
unchecked at that level, and can not see yet how this danger can be
mitigated one level above, where the PortBuilder is used.
- it is still unclear what a »buffer type« actually means; it could
be the pointer type, but it could also imply a class or struct type
to be emplaced into the buffer, which is a special extension to the
`BufferProvider` protocol, yet seems to be used here rather to transport
specific data types required by the actual media handling library (e.g. FFmpeg)
__Analysis__: what kind of verifications are sensible to employ
to cover building, wiring and invocation of render nodes?
Notably, a test should cover requirements and observable functionality,
while ''avoiding direct hard coupling to implementation internals...''
__Draft__: the most simple node builder invocation conceivable...
Code clean-up: mark all buffers with a dedicated tagging type
The point in question is: if we work the LocalTag into the type-hash,
could it be possible to miss an existing entry in the metadata registry?
This could cause two entries to be locked for a single buffer address,
leading to data corruption.
As far as I can see, in the current usage this would not happen,
but unfortunately this problem can not be ruled out, since the BufferProvider
API and protocol is designed to be open for various usage patterns.
However, the same potentially disastrous pattern could also materialise
when registering two different buffer types, and then locking each
for the same buffer location.
...this is a surprisingly tricky issue, since it undercuts the
generic and recursive implementation of buffer handling;
fortunately I've foreseen such demands may arise down the road
and I've reserved an »Local Key« (now renamed into `LocalTag`),
whose meaning is implementation defined and interpreted by
the specific `BufferProvider`
It became clear that a secondary system of connections must be added,
running top-down from a global model context, and thus contrary to the
regular orientation of the node network, which connects upwards from
predecessor to successor, in accordance with the pull principle.
If we accept this wiring as part of the primary structure, it can be
established immediately while building the nodes, thus adding a preconfigured
''pattern of Buffer Descriptors'' to each node, since there is no further
''moving part'' — beyond the wiring to the `BufferProvider`, which thus
becomes part of a global `ModelContext`
As an immediate consequence, the storage for this configuraion should
also be switched to `lib::Several` and handled similar to the primary
node wiring in the Builder...
...especially what is necessary to represent at this level and what information
is implicit; notably there will be an implicit default wiring, but we allow
for case-by-case deviations
To escape a possible deadlock in analysis, I resort to developing
some kind of free-wheeling presupposition how the **Builder** could
be implemented — a centrepiece of the Lumiera architecture envisioned
thus far — which ''unfortunately'' can only be planned and developed
in a more solid way ''after'' the current »Vertical Slice« is completed.
Thus I find myself in the uncomfortable situation of having to work towards
a core piece, which can not yet be built, since it relies heavily on
the very structures to be built...
...and this line of analysis brings us deep into the ''Buffer Provider''
concept developed in 2012 — which appears to be very well to the point
and stands the test of time.
Adding some ''variadic arguments'' at the right place surprisingly leads
to an ''extension point'' — which in turn directly taps into the
still quite uncharted territory interfacing to a **Domain Ontology**;
the latter is assumed to define how to deal with entities and relationships
defined by some media handling library like e.g. FFmpeg.
So what we're set to do here is actually ''ontology mapping....''
The immediate next step is to build some render nodes directly
in a test setting, without using any kind of ''node factory.''
Getting ahead with this task requires to identify the constituents
to be represented on the first code layer for the reworked code
(here ''first layer'' means any part that are ''not'' supplied
by generic, templated building blocks).
Notably we need to build a descriptor for the `FeedManifold` —
which in turn implies we have to decide on some fundamental aspects
of handling buffers in the render process.
To allow rework of the `ProcNode` connectivity, a lot of presumably obsoleted
draft code from 2011 has to be detached, to be able to keep it in-tree
for further reference (until the rework and refactoring is settled).
As outlined in #1367, the integration effort requires some rework
of existing code, which will be driven ahead by the `NodeLinkage_test`
* redefine Node Connectivity
* build simple `ProcNode` directly in scope
* create an `TurnoutSystem` instance
* perform a ''dummy Node-Invocation''
...these features are now used quite regularly,
and so a dedicated documentation test seems indicated.
Actually my intention is to add a tracking allocator to these test helpers
(and then to use that to verify the custom allocator usage of `lib::Several`)
- the starting point is the idea to build a dedicated ''turnout system''
- `StateAdapter`, `BuffTable` ⟶ `FeedManifold` and _Invocation_ will be fused
- actually, the `TurnoutSystem` will be ''pulled'' and orchestrate the invocation
- the structure is assumed to be recursive
The essence of the Node-Invocation, as developed 2009 / 2011 remains intact,
yet it will be organised along a clearer structure
Facing quite some difficulties here, since there are (at least)
two abandoned past efforts towards building a render node network
in the code base; the structure and architecture decisions from these
previous attempts seem largely valid still, yet on a technical level,
the style of construction evolved considerably in the meantime. Moreover,
these old fragments of code, written during the early stages of the
project, were lacking clear goals and anchor points at places;
the situation is quite different now in this respect.
Sticking to well proven practice, the rework will be driven by a test setup,
and will progress over three steps with increasing levels of integration.
In the Lumiera code base, we use C-String constants as unique error-IDs.
Basically this allows to create new unique error IDs anywhere in the code.
However, definition of such IDs in arbitrary namespaces tends to create
slight confusion and ambiguities, while maintaining the proper use statements
requires some manual work.
Thus I introduce a new **standard scheme**
* Error-IDs for widespread use shall be defined _exclusively_ into `namespace lumiera::error`
* The shorthand-Macro `LERR_()` can now be used to simplify inclusion and referral
* (for local or single-usage errors, a local or even hidden definition is OK)
reduce footprint of lib/util.hpp
(Note: it is not possible to forward-declare std::string here)
define the shorthand "cStr()" in lib/symbol.hpp
reorder relevant includes to ensure std::hash is "hijacked" first
In-depth investigation and reasoning highlighted another problem,
which could lead to memory corruption in rare cases; in the end
I found a solution by caching the ''address'' of the current Epoch
and re-validating this address on each Epoch-overflow.
After some difficulties getting any reliable measurement for a Release-build,
it turned out that this solution even ''improves performance by 22%''
Remark-1: the static blockFlow::Config prevents simple measurements by
just recompiling one translation unit; it is necessary to build the
relevant parts of Vault-layer with optimisation to get reliable numbers
Remark-2: performing a full non-DEBUG build highlighted two missing
header-inclusions to allow for the necessary template specialisations.
- use a dedicated context "dropped off" the TestChainLoad instance
- encode the node-idx into the InvocationInstanceID
- build an invocation- and a planning-job-functor
- let planning progress over an lib::UninitialisedStorage array
- plant the ActivityTerm instances into that array as Scheduling progresses
This is Step-2 : change the API towards application
Notably all invocation variants to support member functions
or a reference to bool flags are retracted, since today a
λ-binding directly at usage site tends to be more readable.
The function names are harmonised with the C++ standard and
emergency shutdown in the Subsystem-Runner is rationalised.
The old thread-wrapper test is repurposed to demonstrate
the effectiveness of monitor based locking.
FamilyMember::allocateNextMember() was actually a post-increment,
so (different than with TypedCounter) here no correction is necessary
As an asside, WorkForce_test is sometimes unstable immediately after a build.
Seemingly a headstart of 50µs is not enough to compensate for scheduler leeway
- the deadlock was caused by leaking error state through the C-style lumiera_error
- but the reason for the deadlock lies in the »convenience shortcut«
in the Object-Monitor scope guard for entering a wait state immediately.
This function undermines the unlocking-guarantee, when an exception
emanates from within the wait() function itself.
While it would be straight forward from an implementation POV
to just expose both variants on the API (as the C++ standard does),
it seems prudent to enforce the distinction, and to highlight the
auto-detaching behaviour as the preferred standard case.
Creating worker threads just for one computation and joining the results
seemed like a good idea 30 years ago; today we prefer Futures or asynchronous
messaging to achieve similar results in a robust and performant way.
ThreadJoinable can come in handy however for writing unit tests, were
the controlling master thread has to wait prior to perform verification.
So the old design seems well advised in this respect and will be retained
doing so would contradict the fundamental architecture,
all kinds of failures and timeouts need to be handled within
Scheduler-Layer-2 rather.
Jobs are never aborted, nor do they need to know if and when they are invoked
The second design from 2017, based on a pipeline builder,
is now renamed `TreeExplorer` ⟼ `IterExplorer` and uses
the memorable entrance point `lib::explore(<seq>)`
✔
after completing the recent clean-up and refactoring work,
the monad based framework for recursive tree expansion
can be abandoned and retracted.
This approach from functional programming leads to code,
which is ''cool to write'' yet ''hard to understand.''
A second design attempt was based on the pipeline and decorator pattern
and integrates the monadic expansion as a special case, used here to
discover the prerequisites for a render job. This turned out to be
more effective and prolific and became standard for several exploring
and backtracking algorithms in Lumiera.
An extended series of refactoring and partial rewrites resulted
in a new definition of the `Dispatcher` interface and completes
the buildup of a Job-Planning pipeline, including the ability
to discover prerequisites and compute scheduling deadlines.
At this point, I am about to ''switch to the topic'' of the `Scheduler`,
''postponing'' the completion of the `RenderDrive` until the related
questions regarding memory management and Scheduler interface are settled.
- allow to configure the expected job runtime in the test spec
- remove link to EngineConfig and hard-wire the engine latency for now
... extended integration testing reveals two further bugs ;-)
... document deadline calculation
This finishes the last series of refactorings; the basic concept
remains the same, but in the initial version we arranged the expander
function in the pipeline to maintain a Tuple (parent, child) for the
JobTickets. Unfortunately this turned out to be insufficient, since
JobTicket is effectively const and responsible for a complete Sement,
so there is no room to memorise a Deadline for the parent dependency.
This leads to the better idea to link the JobPlanning aggregators
themselves by parent-child references, which is possible since the
whole dependency chain actually sits in the stack embedded into the
Expander (in the pipeline)
...in the hope that the Optimiser is able to elide those references entirely,
when (as is here the case) they point into another field of a larger object compound
...as a preparation for solving a logical problem with the Planning-Pipeline;
it can not quite work as intended just by passing down the pair of
current ticket and dependent ticket, since we have to calculate a chained
calculation of job deadlines, leading up to the root ticket for a frame.
My solution idea is to create the JobPlanning earlier in the pipeline,
already *before* the expansion of prerequisites, and rather to integrate
the representation of the dependency relation direcly into JobPlanning
...using hard coded values instead of observation of actual runtimes,
but at least the calculation scheme (now relocated from TimeAnchor to JobPlanning)
should be a reasonable starting point.
TODO: test fails...
The initial implementation effort for Player and Job-Planning
has been reviewed and largely reworked, and some parts are now
obsoleted by the reworked alternative and can be disabled.
The basic idea will be retained though: JobPlanning is a
data aggregator and performs the final step of creating a Job
- had to fix a logical inconsistency in the underlying Expander implementation
in TreeExplorer: the source-pipeline was pulled in advance on expansion,
in order to "consume" the expanded element immediately; now we retain
this element (actually inaccessible) until all of the immediate
children are consumed; thus the (visible) state of the PipeFrameTick
stays at the frame number corresponding to the top-level frame Job,
while possibly expanding a complete tree of flexible prerequisites
This test now gives a nice visualisation of the interconnected states
in the Job-Planning pipeline. This can be quite complex, yet I still think
that this semi-functional approach with a stateful pipeline and expand functors
is the cleanest way to handle this while encapsulating all details
- fix a bug in the MockDispatcher, when duplicating the ExitNodes.
A vector-ctor with curly braces will be interpreted as std::initializer_list
- add visualisation of the contents appearing at the end of the pipeline
*** something still broken here, increments don't happen as expected
`steam/engine/mock-dispatcher.hpp |cpp` now integrates this
''complete mock setup for render jobs and frame dispatching.''
The exising `DummyJob` has been slightly adapted and renamed
to `MockJob` and is tightly integrated with the other mocks.
The implementation of a `MockDispatcher` necessitated to change
the use of `MockJobTicket`. The initial attempts used a complete
mock implementation, but this approach turned out not to be viable.
Instead — based on the ideas developed for the mock setup —
now the prospective real implementation of `JobTicket` is available
and will be used by the mock setup too. Instead of a synthetic spec,
now a setup of recursively connected `ExitNode`(s) is used; the latter
seems to develop into some kind of Facade for the render node network.
Based on this mock setup, we can now demonstrate the (mostly) complete
Job-Planning pipeline, starting from a segmentation up to render jobs,
and verify proper connectivity and job invocation.
✔
- has to be prepared / supported by the RenderEnvironmentClosure
- actual translation happens when building the Dispatcher-Pipeline
- implementation delegate through
virtual size_t Dispatcher::resolveModelPort (ModelPort)
...ouch this was insidious: the STL implementation for list does not
return a pointer to the element just allocated, but rather retrieves
and dereferences the back() / front() iterator after returning from emplace_back|front()
...which in case of re-entrant allocations is something wildly different
than the initial allocation. Thus a *cheap* and dirty placeholder implementation
just using a STL container is not possible, and we need at least
to code up likewise cheesy placeholder implementation by hand.
- separate allocation and ctor all
- use an inline buffer in the STL container
- explicitly handle ctor failures to discard allocation
- NOT THREADSAFE and likely WASTFUL in terms of performance
==> MockSupport_test now back to GREEN after complete refactoring
The existing implementation of the Player from 2012~2015 inclduded
an additional differentiation by media channel (for multichannel media)
and would build a separate CalcStream for each channel.
The in-depth analysis conducted for the ongoing »Vertical Slice« effort
revealed that this differentiation is besides the point and would never
be materialised: Since -- by definition -- all media processing has
to be done by the engine, also the generation of the final output format
including any channel multiplexing will happen in render nodes.
The only exception would be when only a single channel of multichannel
media is extracted -- yet this case would then translate into a
dedicated ModelPort.
Based on this reasoning, a lot of complexity (and some contradictions)
within the JobTicket implementation can be removed -- together with
some further leftovers of the fist attempt to build JobTickets always
from a Mock specification (we now use construction by the Segment,
based on an ExitNode, which is the expected actual implementation
for production setup)
...by defining a new scheme for access to custom allocators
...and then passing a reference to such an accessor into the
JobTicket ctor, thereby allowing the ticket istelf recursively
to place further JobTicket instances into the allocation space
--> success, test passes (finally)
Up to now, a draft/mock implementation was used, relying on a »spec tuple«,
which was fabricated by MockJobTicket. But with the introduction of
NodeGraphAttachment, the MockSequence now generates a nested ExitNode structure,
and thus the JobTicket will be created through the "real" ctor, and
no longer via MockJobTicket.
Thus it is possible to skip this whole interspersed »spec tuple«,
since ExitNode *is* already this aggregated / abstracted Spec
PROBLEM: can not implement Spec-generation, since
- we must use a λ for internal allocation of JobTickets
- but recursive type inference is not possible
Will thus need to abandon the Spec-Tuple and relocate this
traversal-and-generation code into JobTicket itself
Use another unit-test (FixtureSegment_test) to guide and cover
the transition from the existing fake-implementation to the
actual implementation, where the JobTicket will be generated
on-demand, from a NodeGraphAttachment
It turns out that the real (not mocked) implementation of JobTicket creation
is already required now for this planned (mock)Dispatcher setup;
moreover, this real implementation turns out to be almost identical
to the mock implementation written recently -- just nested structure
of prerequiste JobTickets need to be changed into a similar structur
of ExitNodes
-- as an aside: rearrange various tests to be more in-line
with the envisioned architecture of playback and engine
...this opens up yet another difficult question and a host of new problems
- how are prerequisites detected or arranged by the Builder
- how are prerequisites represented?
- what is an ExitNode in terms of implementation? A subclass of ProcNode?
- how will the actual implementation of JobTicket creation (on-demand) work?
- how to adapt the Mock implementation, while retaining the Specification
for Segments and prerequisites?
...it turns out that we actually do not need to wrap TreeExplorer
on the builder types, because basically there is only a single active
builder type, and the complete processing pipeline can be assembled
in a single terminal function.
The type rebinding problem can thus be solved just by a simple
marker struct, which inherits from a template parameter
...hard to tackle...
The idea is to wrap the TreeExplorer builder, so that our specific
builder functions can delegated to the (inherited) generic builder functions
and would just need to supply some cleverly bound lambdas. However,
resulting types are recursive, which does not play nice with type inference,
and working around that problem leads to capturing a self reference,
which at time of invocation is already invalidated (due to moving the
whole pipeline into the final storage)
...which leads to the next daunting problems:
- we need some mocked ModelPort and DataSink placeholders
- we need a way how to inherit from a partial TreeExplorer pipeline
several years ago, it seemed like a good idea to incorporate
the link between nominal time and wall-clock time into a dedicated
anchor point, which also regulates the continued frame planning.
But it turned out that such a design mixes up several concepts
and introduces confusion regarding the meaning of "real time"
- latency can not be reasonably defined for a whole planning chunk
- skipping or sliding due to missed deadlines can not reasonably handled
within such an abstract entity; it must be handled rather at the
level of a playback process
- linking the frame grid generation directly to a planning chunk
undercuts the possible abstraction of a planning pipeline
...which is build a »Job planning pipeline« step by step
in a test setup, and then factor that out as RenderDrive,
to supersede the existing CalcPlanContinuation and get
rid of the Monads this way...
Challenges
- there is a inconsistency with channel usage
- need to establish a way how to transport the output-Sink into the JobFunctor
- need a way to propagate the current frame number to the next planning chunk
The prototypical setup of data structures and test support components
is largely complete by now — with the exception of the `MockDispatcher`,
which will be completed while moving to the next steps pertaining the
setup of a frame dispatch pipeline.
* the existing `DummyJob` was augmented to allow verification of
association between Job and `JobTicket`
* the existing implementation of `JobTicket` was verified and augmented
to allow coverage of the whole usage cycle
* a `MockJobTicket` was implemented on top, which can be generated
from a symbolical test specification (rather than from the real
Fixture data structure)
* a complete `MockSegmentation` was developed, allowing to establish
all the aforementioned data structures without an actual backing
Render Engine. Moreover, `MockSegmentation` can be generated
from the aforementioned symbolic test specification.
* as part of this work, an algorithm to split an existing Segmentation
and to splice in new segments was developed and verified
Last testcase: add deeply nested Prerequisites.
Turns out that the allocator must be able to handle
re-entrant allocations, which std::deque can not fulfil.
Thus using std::list here for the Mock implementation.
In the end, the real allocations will be done by our custom
allocator (AllocationCluster), which can be arranged easily
to support re-entrant allocation calls (since the whole point
is to just place those objects into a pre-allocated large block
and only de-allocate them later in one sway. Thus the allocator
does not need to wait for the object constructor to finish, which
trivially allows for re-entrant calls)
...which uncovers further deeply nested problems,
especially when referring to non-copyable types.
Thus need to construct a common type that can be used
both to refer to the source elements and the expanded elements,
and use this common type as result type and also attempt to
produce better diagnostic messages on type mismatch....
To complete the mock setup, the next step would be to extend the GenNode-based spec langage
to allow defining prerequisite Mock-JobTickets. Setting this up seems rather straight forward --
however, defining a simple testcase to cover this extension runs into surprisingly tricky problems..
- for one, the singleValIterator from Itertools has serious difficulties handling references
- but even more surprising, it seems impossible to make the "prerequisites iterator"
fit into the Tree-Explorer framework (which I intend to use as replacement
for the monadic approach)
after some extended analysis of generic types and template instances,
it seems that not TreeExplorer as such is the primary problem, but rather
there is a conceptual mismatch somewhere deep down in Itertools or Iter-Adapter
By reasoning and analysis I conclude that the differentiation into
multiple channels is likely misplaced in JobTicket; it belongs ratther
into the Segment and should provide a suitable JobTicket for each ModelPort
Handling of prerequisites also needs to be reshaped entirely after
switching to a pipeline builder for the Job-planning pipeline; as
preliminary access point, just add an iterator over the immediate
prerequisites, thereby shifting the exploration mechanism entirely
out of the JobTicket implementation
Testcase: A simple Sementation with a single and bounded Segment
As aside, figured out how to unpack an iterator such as to
tie a fixed number of references through a structural binding:
auto const& [s1,s2,s3] = seqTuple<3> (mockSegs.eachSeg());
...now able to build a mock segmentation which issues dummy jobs,
and is wired such as to verify the right job is invoked for each segment.
And this allows to build and verify the Dispatcher,
without being able to invoke actual render jobs yet.
There are 12 distinct cases regarding the orientation of two intervals;
The Segmentation::splitSplice() operation shall insert a new Segment
and adjust / truncate / expand / split / delete existing segments
such as to retain the *Invariant* (seamless segmentation covering
the complete time axis)
- how to pass-in a specification given as GenNode
- now this might be translated into a MockJobTicket allocated in the MockSegmentation
Unimplemented: actually build the Segment with suitable start/end time
right now we're lacking a complete working implementation of render node invocation,
and thus the Dispatcher implementation can only be verified with the help
of mocked jobs. However, at least a preliminary implementation of tagging the
invocation instance is available, and thus we're able to verify that
a given job instance indeed belongs to and is "backed" by a specific JobTicket.
This is prerequisite for building up a (likewise mocked) Fixture datastructure,
and this in turn was meant to form the basis for attacking an actual Scheduler
implementation, followed by a real render node invocation.
- can now create a Job from JobTicket::NIL
- on invocation this Job will to nothing
Only when the first real output backend is implemented,
we can decide if this simplistic implementation is enough,
or if an empty output must be explicitly generated...
* using a simplified preliminary implementation of hash chaining (see #1293)
* simplistic implementation of hashing for time values (half-rotation)
* for now just hashing the time into the upper part of the LUID
Maybe we can even live with that implementation for some time,
depending on how important uniform distribution of hash values is
for proper usage of the frame cache.
Needless to say, various further fine points need more consideration,
especially questions of portability (32bit anyone?). Moreover, since
frame times are typically quantised, the search space for the hashed
time values is drastically reduced; conceivably we should rather
research and implement a good hash function for 128bit and then combine
all information into a single hash key....
...using the MockJobTicket setup as point of reference,
since the actual invocation of render nodes will only be drafted
later in this "Vertical Slice" integration effort...
- introduce a JobTicket::NOP (null-object pattern)
- assuming that the function splitSplice() will retain complete coverage allways
Remark:
`Fixture::getPlaylistForRender()` is a leftover from the very early implementation drafts.
This function was more or less based on the way Cinelerra works; it is clear by now
that Lumiera can not possibly work this way, given that we'll build a low-level model
and dispatch precompiled render jobs....
The Fixture and the low-level model backbone deserve a distinct namespace on their own.
Since it's built by the Builder from the Session contents, and also used by the frame dispatch,
we can expect dependence on some types from Steam-Layer, and thus this namespace
needs to reside in Steam-Layer rather, while the actual low-level Model
might become part of Vault-Layer, creating a hierarchy of data structures.
(Remark: likely also the session related namespaces will need a reorganisation)
The idea is to escape a "design deadlock" by using a test-driven prototype
implementation of the data structure to back a further development
of the Dispatcher and Scheduler implementation, which then can be used
to gradually elaborate and switch over to an actual implementation
data structure
...requires a first attempt towards defining a `JobTiket`.
This turns out quite tricky, due to using those `LinkedElements`
(intrusive single linked list), which requires all added records
actually to live elsewhere. Since we want to use a custom allocator
later (the `AllocationCluster`), this boils down to allocating those
records only when about to construct the `JobTicket` itself.
What makes matters even worse: at the moment we use a separate spec
per Media channel (maybe these specs can be collapsed later non).
And thus we need to pass a collection -- or better an iterator
with raw specs, which in turn must reveal yet another nested
sequence for the prerequisite `JobTickets`.
Anyhow, now we're able at least to create an empty `JobTicket`,
backed by a dummy `JobFunctor`....
Looks like we'll actually retain and use this low-level solution
in cases where we just can not afford heap allocations but need
to keep polymorphic objects close to one another in memory.
Since single linked lists are filled by prepending, it is rather
common to need the reversed order of elements for traversal,
which can be achieved in linear time.
And while we're here, we can modernise the templated emplacement functions
- build the reworked Job-planning pipeline more or less from scratch
- back that with mocked `Dispatcher` and `JobTicket`
- then transfer this into a `RenderDrive`, which can be tested as well
- could continue then to a `CalcStream` integration test....
- decision: the Monad-style iteration framework will be abandoned
- the job-planning will be recast in terms of the iter-tree-explorer
- job-planning and frame dispatch will be disentangled
- the Scheduler will deliberately offer a high-level interface
- on this high-level, Scheduler will support dependency management
- the low-level implementation of the Scheduler will be based on Activity verbs
The APIs for time quantisation were drafted in an early stage of the project
and then never followed-up. Especially Grid::gridAlign has no
real-world usage yet, and is only massaged in some tests.
When looking at QuantiserBasics_test, I was puzzled and led astray,
since this function suggests to materialise a continuous time into
a quantised time -- which it doesn't (there is another dedicated
function Quantiser::materialise() to that end); so, without engaging
into the discussion if this function is of any use, I'll hereby
choose a name better reflecting what it does.
...in an attempt to clarify why numerous cross links are not generated.
In the end, this attempt was not very successful, yet I could find some breadcrumbs...
- file comments generally seem to have a problem with auto link generation;
only fully qualified names seem to work reliably
- cross links to entities within a namespace do not work,
if the corresponding namespace is not documented in Doxygen
- documentation for entities within anonymous namespaces
must be explicitly enabled. Of course this makes only sense
for detailed documentation (but we do generate detailed
documentation here, including implementation notes)
- and the notorious problem: each file needs a valid @file comment
- the hierarchy of Markdown headings must be consistent within each
documentation section. This entails also to individual documented
entities. Basically, there must be a level-one heading (prefix "#"),
otherwise all headings will just disappear...
- sometimes the doc/devel/doxygen-warnings.txt gives further clues
the reason for the failure, as it turned out,
is that 'noexcept' is part of the function signature since C++17
And, since typically a STL container has const and non-const variants
of the begin() and end() function, the match to a member function pointer
became ambuguous, when probing with a signature without 'noexcept'
However, we deliberately want to support "any STL container like" types,
and this IMHO should include types with a possibly throwing iterator.
The rationale is, sometimes we want to expose some element *generator*
behind a container-like interface.
At this point I did an investigation if we can emulate something
in the way of a Concept -- i.e. rather than checking for the presence
of some functions on the interface, better try to cover the necessary
behaviour, like in a type class.
Unfortunately, while doable, this turns out to become quite technical;
and this highlights why the C++20 concepts are such an important addition
to the language.
So for the time being, we'll amend the existing solution
and look ahead to C++20
as it turns out, "almost" the whole codebase compiles in C++17 mode.
with the exception of two metaprogramming-related problems:
- our "duck detector" for STL containers does not trigger anymore
- the Metafunction to dissect Function sigantures (meta::_Fun) flounders
When drafting the time handling framework some years ago,
I foresaw the possible danger of mixing up numbers relating
to fractional seconds, with other plain numbers intended as
frame counts or as micro ticks. Thus I deliberately picked
an incompatible integer type for FSecs = boost::rational<long>
However, using long is problematic in itself, since its actual
bit length is not fixed, and especially on 32bit platforms long
is quite surprisingly defined to be the same as int.
However, meanwhile, using the new C++ features, I have blocked
pretty much any possible implicit conversion path, requiring
explicit conversions in the relevant ctor invocations. So,
after weighting in the alternatives, FSecs is now defined
as boost::rational<int64_t>.
This was prompted by a test failing under Boost-1.65 (--> see #294)
When reviewed now, the whole idea of testing Steam-Layer Commands for
equivalence feels a bit sketchy.
Just the comparison for the command ''identity'' alone seems sufficient,
i.e. the test if a command-ID is associated with the same backend-handle
and thus the same functor binding.
- we got occasional hangups when waiting for disabled state
- the builder was not triggered properly, sometimes redundant, sometimes without timeout
As it turned out, the loop control logic is more like a state machine,
and the state variables need to be separated from the external influenced variables.
As a consequence, the inChange_ variable was not calculated properly when disabled in a race,
and then the loop went into infinite wait state, without propagating this to
the externally waiting client, which caused the deadlock
basically we can pick just any convention here, and so we should pick the convention in a way
that makes most sense informally, for a *human reader*. But what we previously did, was to pick
the condition such as to make it simple in some situations for the programmer....
With the predictable result: even with the disappointingly small number of usages we have up to now,
we got that condition backwards several times.
OK, so from now on!!!
Time::NEVER == Time::MAX, because "never" is as far as possible into the future
- most notably the NOBUG logging flags have been renamed now
- but for the configuration, I'll stick to "GUI" for now,
since "Stage" would be bewildering for an occasional user
- in a similar vein, most documentation continues to refer to the GUI
...it should have been explicit from start, since there is no point
in converting an EntryID into a plain flat string without further notice
this became evident, when the compiler picked the string overload on
MakeRec().genNode(specialID)
...which is in compliance to the rules, since string is a direct match,
while BareEntryID would be an (slicing) upcast. However, obviously we
want the BareEntryID here, and not an implicit string conversion,
thereby discarding the special hash value hidden within the ID
As it turns out, using the functional-notation form conversion
with *parentheses* will fall back on a C-style (wild, re-interpret) cast
when the target type is *not* a class. As in the case in question here, where
it is a const& to a class. To the contrary, using *curly braces* will always
attempt to go through a constructor, and thus fail as expected, when there is
no conversion path available.
I wasn't aware of that pitfall. I noticed it since the recently introduced
class TimelineGui lacked a conversion operator to BareEntryID const& and just
happily used the TimelineGui object itself and did a reinterpret_cast into BareEntryID
I am fully aware this change has some far reaching ramifications.
Effectively I am hereby abandoning the goal of a highly modularised Lumiera,
where every major component is mapped over the Interface-System. This was
always a goal I accepted only reluctantly, and my now years of experience
confirm my reservation: it will cost us lots of efforts just for the
sake of being "sexy".
- state-of-the-art implementation of access with Double Checked Locking + Atomics
- improved design for configuration of dependencies. Now at the provider, not the consumer
- support for exposing services with a lifecycle through the lib::Depend<SRV> front-end
IterSource should be refactored to have an iteration control API similar to IterStateWrapper.
This would resolve the need to pass that pos-pointer over the abstraction barrier,
which is the root cause for all the problems and complexities incurred here
after extended analysis, it turned out to be a "placeholder concept"
and introduces an indirection, which can be removed altogether
- simple command invocation happens at gui::model::Tangible
- it is based on the command (definition) ID
- instance management happens automatically and transparently
- the extended case of context-bound commands will be treated later,
and is entirely self-contained
due to the refactorings, the instance was moved out prior to checking for
bound arguments. This is ammended now, albeit at the price of passing an
additional flagn and some tricky boolean conditions
in accordance to the design changes concluded yesterday.
- in the standard cases we now check the global registry first
- automatically create anonymous clone copy from global commands
- reorganise code internally to use common tail implementation
as it turns out, we can always trigger commands right away,
the moment all arguments are known. Thus it is sufficient to
send a single argument binding message, which allows us to
get rid of a lot or ugly complexities (payload visitor).
It seems more adequate to push the somewhat intricate mechanics
for the "fall back" onto generic commands down into the implementation
level of CommandInstanceManager. The point is, we know the standard
usage situation is to rely on the instance manager, and thus we want
to avoid redundant table lookups, only to support the rare case of
fallback to global commands. The latter is currently used only from
unit-tests, but might in future also be used by scripts.
Due to thread safety considerations, I have refrained from handing
out a direct reference to the command token sitting in the registry,
even while not doing so incurs a small runtime penalty (accessing
the shared ref-count for creating a copy of the smart-handle).
This is the typical situation where you'd be tempted to sacrifice
sanity for the sake of an imaginary performance benefit, which
in fact is dwarfed by all the machinery of UI-Bus and argument
passing via GenNode.
