ComputeGraph concurrency

[ffreyer]

Description

This is another attempt at getting ComputeGraph updates and resolution working concurrently, without just placing everything behind a global lock.

This version includes locks for every edges which get locked behind a global lock before resolve!() does work. The edge locks then release once the edges outputs are no longer in use by any child edge. mark_dirty!() locks the global lock as resolve!() preparation requires state to be frozen. mark_dirty!(computed) also locks the parent edge of the compute note it marks because it sets state used in edge resolution. Updates lock their parent edge for the same reason. update!() specifically lock the parent edge of all the inputs being set together, so the update remains synchronized.

Notes:

• Updating a node from within a computegraph callback may corrupt state (if the lock passes) or cause a deadlock (if it doesn't) or do nothing bad (if the edge is not an active part of this resolution anymore. This means it's not a direct parent of the edge causing the update and there is no other way to reach it from any (recursive) child of the edge causing the update.)

Performance:
This is 10-20% slower than #5546 for me when rendering a simple plot in an Axis with the camera moving the Axis each frame.

f, a, p = scatter(rand(Point2f, 100))
screen = display(f)
e = events(f)
begin # compile interaction
    e.mouseposition[] = (200.0, 200.0) .+ 50.0 .* (cos(0), sin(0))
    e.mousebutton[] = Makie.MouseButtonEvent(Mouse.right, Mouse.press)
    e.mouseposition[] = (200.0, 200.0) .+ 50.0 .* (cos(0.5), sin(0.5))
    yield()
    e.mousebutton[] = Makie.MouseButtonEvent(Mouse.right, Mouse.release)
end

@time timings = let
    e = events(f)
    e.mouseposition[] = (200.0, 200.0) .+ 50.0 .* (cos(0), sin(0))
    e.mousebutton[] = Makie.MouseButtonEvent(Mouse.right, Mouse.press)
    idx = 1
    timings = GLMakie.render_asap(screen, 10_000) do
        e.mouseposition[] = (200.0, 200.0) .+ 50.0 .* (cos(0.03 * idx), sin(0.03 * idx))
        idx += 1
    end
    e.mousebutton[] = Makie.MouseButtonEvent(Mouse.right, Mouse.release)
    timings
end

# ms frametimes
mean(timings) * 1000
median(timings) * 1000
mean(sort(timings)[1:900]) * 1000

TODO:

• Consider swapping out the global lock for a lock shared between all connected graphs. (I.e. if graph A feeds into graph B, they both must have the same lock to correctly protect resolve setup)
• Consider some sort of asymmetric (global/multi-graph) lock for update/mark_dirty vs resolve which allows nothing else to run while resolve is setting up, but does allow multiple mark_dirty's to run at the same time. Multiple overlapping mark_dirty's will, at worst, do duplicate work, marking the same edge.dirty[] = true multiple times. Updates still have edge locks to protect against overwrite.
• guard against nested resolve triggered by Observable (i.e. don't allow an update from resolve to trigger another resolve through onchange. This should allow inputs to be updated in a loop even if they trigger an Observable)

Type of change

Delete options that do not apply:

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

Checklist

• Added an entry in CHANGELOG.md (for new features and breaking changes)
• Added or changed relevant sections in the documentation
• Added unit tests for new algorithms, conversion methods, etc.
• Added reference image tests for new plotting functions, recipes, visual options, etc.

[MakieBot]

Benchmark Results

SHA: 00d86f538712d0e3103667348f51136234abfc89

Warning

These results are subject to substantial noise because GitHub's CI runs on shared machines that are not ideally suited for benchmarking.