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discovery+graph: track job set dependencies in vb #9241

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@Crypt-iQ Crypt-iQ commented Nov 1, 2024

This PR changes the ValidationBarrier to track abstract job dependencies. This just means that every time a child job comes in (i.e. channel update or node announcement), we track the set of possible parent jobs that are related to it (channel announcement(s)) that have registered via InitJobDependencies. The goroutines containing the child jobs will then wait to be notified every time one of their parent jobs completes. From the child job's POV, this just works as ref-counting except that you're only counting the parent jobs you're interested in.

With this, we can now extend the ValidationBarrier to track any sort of abstract job that requires both concurrency and waiting for another job to finish. It also makes it possible in a future PR to very easily make node announcements depend on channel announcements. See the commit messages for more details.

TODO:

  • Introduce a test to simulate goroutines randomly calling into the ValidationBarrier and ensure that all child jobs finish after their related parent jobs.
  • If time permits, write a fuzz test for the above as well.
  • Continue testing on mainnet

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@Crypt-iQ Crypt-iQ force-pushed the fix_vb branch 3 times, most recently from 7acf321 to fc00572 Compare November 4, 2024 18:56
@Crypt-iQ Crypt-iQ changed the title [DRAFT] graph: fix validation barrier [DRAFT] discovery+graph: track job set dependencies in ValidationBarrier Nov 4, 2024
@Crypt-iQ Crypt-iQ changed the title [DRAFT] discovery+graph: track job set dependencies in ValidationBarrier [DRAFT] discovery+graph: track job set dependencies in vb Nov 4, 2024
@Crypt-iQ Crypt-iQ force-pushed the fix_vb branch 3 times, most recently from fc72083 to 7d95cd2 Compare November 6, 2024 18:19
@Crypt-iQ Crypt-iQ marked this pull request as ready for review November 6, 2024 18:46
@Crypt-iQ Crypt-iQ changed the title [DRAFT] discovery+graph: track job set dependencies in vb discovery+graph: track job set dependencies in vb Nov 6, 2024
@saubyk saubyk added this to the v0.19.0 milestone Nov 7, 2024
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saubyk commented Nov 7, 2024

cc: @gijswijs for review

graph/builder.go Show resolved Hide resolved
graph/validation_barrier.go Outdated Show resolved Hide resolved
fn/set.go Outdated Show resolved Hide resolved
func (v *ValidationBarrier) SignalDependants(job interface{}, allow bool) {
// SignalDependents signals to any child jobs that this parent job has
// finished.
func (v *ValidationBarrier) SignalDependents(job interface{}, id JobID) error {
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haha sneaky change from British spelling to American 😝

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this has been driving me crazy for years

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I'm finding the distinction between parent and child jobs here both confusing and unnecessary. What we have here is a dependency graph of undifferentiated jobIDs. once all of the dependencies have run we can run. once we run we want to signal all of our dependents. We should be able to accomplish this with a single removeJob that does this index cleanup and dependent signaling.

The main difficulty I'm noticing in this PR is that we have multiple IDs that we want to be able to map to JobIDs from disjoint domains. My recommendation here is to make the core algebra of this component undifferentiated and then have auxilliary mappings that help recover the relevant JobID from the other unique protocol identifiers.

fn/set.go Outdated Show resolved Hide resolved
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graph/validation_barrier.go Outdated Show resolved Hide resolved
annID = msg.ShortChannelID

// TODO: If ok is false, we have serious issues.
parentJobIDs, ok = v.jobDependencies[childJobID]
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why does this read not need a mutex lock?

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it's locked above no?

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Comment on lines 417 to 421
// We don't want to block when sending out the signal.
select {
case notifyChan <- struct{}{}:
default:
}
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Are we ok with swallowing the signal instead? Seems like this could case jobs to never be run, particularly if lastJob is true

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I'm not sure what you mean here. 1. How would jobs not be run in the current scenario? 2. What does swallowing the signal look like here?

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saubyk commented Nov 19, 2024

cc: @gijswijs for review

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Crypt-iQ commented Dec 6, 2024

Outstanding things to do:

  • change from any to a union for map keys
  • update fn package to have a set copy method

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@Crypt-iQ - is this ready for re-review given the itest failures?

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Crypt-iQ commented Dec 9, 2024

@Crypt-iQ - is this ready for re-review given the itest failures?

Sorry no, it seems like I broke something

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Crypt-iQ commented Dec 9, 2024

Ready for review now, had an issue with any being a key so I think the type change mentioned above is a blocker.

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@Crypt-iQ - defs ready given all the failures?

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@Crypt-iQ - defs ready given all the failures?

now it is, the fn change broke it

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change from any to a union for map keys

I could not figure out a decent way to use generics to accomplish this, so jobInfoMap just has string keys now.

update fn package to have a set copy method

will update this code with Copy once #9374 is merged and a new fn is tagged

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I really like this change. 👍 Somehow, for me, the old solution with the depency maps is harder to reason about. I like the concept of jobInfoMap better.

One thing I found (somewhat in line with @ProofOfKeags earlier comment) is that the usage of the words dependency, dependent and parent, child respectively is inconsistent throughout. The code would be more readable if we would stick to one pair. If we choose parent/child we don't need to fight anymore about british vs us spelling, which is an added benefit.

Apart from that I made some small comments in the code.

graph/validation_barrier.go Outdated Show resolved Hide resolved
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graph/validation_barrier.go Outdated Show resolved Hide resolved
jobDesc = fmt.Sprintf("job=lnwire.NodeAnnouncement, pub=%s",
vertex)
route.Vertex(msg.NodeID))

// Other types of jobs can be executed immediately, so we'll just
// return directly.
case *lnwire.AnnounceSignatures1:
// TODO(roasbeef): need to wait on chan ann?
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Maybe return nil here and remove the following block below:

// If it's not ok, it means either the job is not a dependent type, or
	// it doesn't have a dependency signal. Either way, we can return
	// early.
	if !ok {
		return nil
	}

Same for the case after this one.

Less loc and to my mind clearer intent.

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Done

default:
}

// If this is the last parent job for this id, also
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nit

Suggested change
// If this is the last parent job for this id, also
// If this is the last parent job for this annID, also

Or I could not be understanding this properly.

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Yup that's correct it should have been annID. Is it more clear now?

graph/validation_barrier.go Outdated Show resolved Hide resolved
@@ -120,11 +131,19 @@ func TestValidationBarrierQuit(t *testing.T) {
// Signal completion for the first half of tasks, but only allow
// dependents to be processed as well for the second quarter.
case i < numTasks/4:
barrier.SignalDependants(anns[i], false)
err := barrier.SignalDependents(
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Without the deny and allow logic the first case can be removed. There is no difference with the second case anymore, right?

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Correct, good catch

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This omits calls to InitJobDependencies, SignalDependants, and
WaitForDependants. These changes have been made here because
the router / builder code does not actually need job dependency
management. Calls to the builder code (i.e. AddNode, AddEdge,
UpdateEdge) are all blocking in the gossiper. This, combined
with the fact that child jobs are run after parent jobs in the
gossiper, means that the calls to the router will happen in the
proper dependency order.
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@ellemouton: review reminder
@Crypt-iQ, remember to re-request review from reviewers when ready

This commit does two things:
- removes the concept of allow / deny. Having this in place was a
  minor optimization and removing it makes the solution simpler.
- changes the job dependency tracking to track sets of abstact
  parent jobs rather than individual parent jobs.

As a note, the purpose of the ValidationBarrier is that it allows us
to launch gossip validation jobs in goroutines while still ensuring
that the validation order of these goroutines is adhered to when it
comes to validating ChannelAnnouncement _before_ ChannelUpdate and
_before_ NodeAnnouncement.
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Crypt-iQ commented Jan 3, 2025

Addressed comments, but may need to hold off on upgrading the fn package since there were some changes that prevents me from upgrading to 2.0.7.. We can still get this through without changing fn if we misuse the API a little bit (in a safe way).

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