nimbus-eth2/beacon_chain/validators/action_tracker.nim

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# beacon_chain
# Copyright (c) 2021-2022 Status Research & Development GmbH
# Licensed and distributed under either of
# * MIT license (license terms in the root directory or at https://opensource.org/licenses/MIT).
# * Apache v2 license (license terms in the root directory or at https://www.apache.org/licenses/LICENSE-2.0).
# at your option. This file may not be copied, modified, or distributed except according to those terms.
import
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std/[sequtils, tables],
stew/shims/[sets, hashes], chronicles,
eth/p2p/discoveryv5/random2,
../spec/forks,
../consensus_object_pools/spec_cache
export forks, tables, sets
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when (NimMajor, NimMinor) < (1, 4):
{.push raises: [Defect].}
else:
{.push raises: [].}
const
SUBNET_SUBSCRIPTION_LEAD_TIME_SLOTS* = 4
## The number of slots before we're up for aggregation duty that we'll
## actually subscribe to the subnet we're aggregating for - this gives
## the node time to find a mesh etc - can likely be further trimmed
KNOWN_VALIDATOR_DECAY* = 3 * SLOTS_PER_EPOCH
## The number of slots before we "forget" about validators that have
## registered for duties - once we've forgotten about a validator, we'll
## eventually decrease the number of stability subnets we're subscribed to.
## Active validators are expected to register for duty every epoch - we use
## 3 epochs here to counter rounding errors and communication delays.
## When known validators decrease, we will keep the stability subnet around
## until it "naturally" expires.
type
AggregatorDuty* = object
subnet_id*: SubnetId
slot*: Slot
ActionTracker* = object
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rng: ref HmacDrbgContext
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subscribeAllAttnets: bool
currentSlot: Slot
## Duties that we accept are limited to a range around the current slot
subscribedSubnets*: AttnetBits
## All subnets we're currently subscribed to
stabilitySubnets: seq[tuple[subnet_id: SubnetId, expiration: Epoch]]
## The subnets on which we listen and broadcast gossip traffic to maintain
## the health of the network - these are advertised in the ENR
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nextCycleEpoch: Epoch
# Used to track the next attestation and proposal slots using an
# epoch-relative coordinate system. Doesn't need initialization.
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attestingSlots: array[2, uint32]
proposingSlots: array[2, uint32]
lastCalculatedEpoch*: Epoch
attesterDepRoot*: Eth2Digest
## The latest dependent root we used to compute attestation duties
## for internal validators
knownValidators*: Table[ValidatorIndex, Slot]
## Validators that we've recently seen - we'll subscribe to one stability
## subnet for each such validator - the slot is used to expire validators
## that no longer are posting duties
duties: HashSet[AggregatorDuty]
## Known aggregation duties in the near future - before each such
## duty, we'll subscribe to the corresponding subnet to collect
## attestations for the aggregate
lastSyncUpdate*: Opt[SyncCommitteePeriod]
syncDuties*: Table[ValidatorPubKey, Epoch]
func hash*(x: AggregatorDuty): Hash =
hashAllFields(x)
# https://github.com/ethereum/consensus-specs/blob/v1.3.0-alpha.1/specs/phase0/validator.md#phase-0-attestation-subnet-stability
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func randomStabilitySubnet(
self: ActionTracker, epoch: Epoch): tuple[subnet_id: SubnetId, expiration: Epoch] =
(
self.rng[].rand(ATTESTATION_SUBNET_COUNT - 1).SubnetId,
epoch + EPOCHS_PER_RANDOM_SUBNET_SUBSCRIPTION +
self.rng[].rand(EPOCHS_PER_RANDOM_SUBNET_SUBSCRIPTION.int).uint64,
)
proc registerDuty*(
tracker: var ActionTracker, slot: Slot, subnet_id: SubnetId,
vidx: ValidatorIndex, isAggregator: bool) =
# Only register relevant duties
if slot < tracker.currentSlot or
slot + (SLOTS_PER_EPOCH * 2) <= tracker.currentSlot:
debug "Irrelevant duty", slot, subnet_id, vidx
return
tracker.knownValidators[vidx] = slot # Update validator last-seen registry
if isAggregator:
let newDuty = AggregatorDuty(slot: slot, subnet_id: subnet_id)
if newDuty in tracker.duties:
return
debug "Registering aggregation duty", slot, subnet_id, vidx
tracker.duties.incl(newDuty)
proc registerSyncDuty*(
tracker: var ActionTracker, pubkey: ValidatorPubKey, until_epoch: Epoch) =
if tracker.currentSlot.epoch >= until_epoch:
return
tracker.syncDuties.withValue(pubkey, entry) do:
if entry[] < until_epoch:
debug "Updating sync duty",
pubkey = shortLog(pubkey), prev_until_epoch = entry[], until_epoch
entry[] = until_epoch
reset(tracker.lastSyncUpdate)
do:
debug "Registering sync duty", pubkey = shortLog(pubkey), until_epoch
tracker.syncDuties[pubkey] = until_epoch
reset(tracker.lastSyncUpdate)
proc hasSyncDuty*(
tracker: ActionTracker, pubkey: ValidatorPubKey, epoch: Epoch): bool =
epoch < tracker.syncDuties.getOrDefault(pubkey, GENESIS_EPOCH)
const allSubnetBits = block:
var res: AttnetBits
for i in 0..<res.len: res[i] = true
res
func aggregateSubnets*(tracker: ActionTracker, wallSlot: Slot): AttnetBits =
var res: AttnetBits
# Subscribe to subnets for upcoming duties
for duty in tracker.duties:
if wallSlot <= duty.slot and
wallSlot + SUBNET_SUBSCRIPTION_LEAD_TIME_SLOTS > duty.slot:
res[duty.subnet_id.int] = true
res
func stabilitySubnets*(tracker: ActionTracker, slot: Slot): AttnetBits =
if tracker.subscribeAllAttnets:
allSubnetBits
else:
var res: AttnetBits
for v in tracker.stabilitySubnets:
res[v.subnet_id.int] = true
res
proc updateSlot*(tracker: var ActionTracker, wallSlot: Slot) =
# Prune duties from the past - this collection is kept small because there
# are only so many slot/subnet combos - prune both internal and API-supplied
# duties at the same time
tracker.duties.keepItIf(it.slot >= wallSlot)
block:
var dels: seq[ValidatorPubKey]
for k, v in tracker.syncDuties:
if wallSlot.epoch >= v:
dels.add k
for k in dels:
tracker.syncDuties.del(k)
# Keep stability subnets for as long as validators are validating
var toPrune: seq[ValidatorIndex]
for k, v in tracker.knownValidators:
if v + KNOWN_VALIDATOR_DECAY < wallSlot: toPrune.add k
for k in toPrune:
debug "Validator no longer active", index = k
tracker.knownValidators.del k
# One stability subnet per known validator
static: doAssert RANDOM_SUBNETS_PER_VALIDATOR == 1
# https://github.com/ethereum/consensus-specs/blob/v1.3.0-alpha.1/specs/phase0/validator.md#phase-0-attestation-subnet-stability
let expectedSubnets =
min(ATTESTATION_SUBNET_COUNT.int, tracker.knownValidators.len)
let epoch = wallSlot.epoch
block:
# If we have too many stability subnets, remove some expired ones
var i = 0
while tracker.stabilitySubnets.len > expectedSubnets and
i < tracker.stabilitySubnets.len:
if epoch >= tracker.stabilitySubnets[i].expiration:
tracker.stabilitySubnets.delete(i)
else:
inc i
for ss in tracker.stabilitySubnets.mitems():
if epoch >= ss.expiration:
ss = tracker.randomStabilitySubnet(epoch)
# and if we have too few, add a few more
for i in tracker.stabilitySubnets.len..<expectedSubnets:
tracker.stabilitySubnets.add(tracker.randomStabilitySubnet(epoch))
tracker.currentSlot = wallSlot
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func getNextValidatorAction(
actionSlotSource: auto, lastCalculatedEpoch: Epoch, slot: Slot): Slot =
# The relevant actions are in, depending on calculated bounds:
# [aS[epoch mod 2], aS[1 - (epoch mod 2)]]
# current epoch next epoch
let orderedActionSlots = [
actionSlotSource[ slot.epoch mod 2'u64],
actionSlotSource[1 - (slot.epoch mod 2'u64)]]
static: doAssert MIN_ATTESTATION_INCLUSION_DELAY == 1
# Cleverer ways exist, but a short loop is fine. O(n) vs O(log n) isn't that
# important when n is 32 or 64, with early exit on average no more than half
# through.
for i in [0'u64, 1'u64]:
let bitmapEpoch = slot.epoch + i
if bitmapEpoch > lastCalculatedEpoch:
return FAR_FUTURE_SLOT
for slotOffset in 0 ..< SLOTS_PER_EPOCH:
let nextActionSlot = start_slot(bitmapEpoch) + slotOffset
if ((orderedActionSlots[i] and (1'u32 shl slotOffset)) != 0) and
nextActionSlot > slot:
return nextActionSlot
FAR_FUTURE_SLOT
func getNextAttestationSlot*(tracker: ActionTracker, slot: Slot): Slot =
getNextValidatorAction(
tracker.attestingSlots,
tracker.lastCalculatedEpoch, slot)
func getNextProposalSlot*(tracker: ActionTracker, slot: Slot): Slot =
getNextValidatorAction(
tracker.proposingSlots,
tracker.lastCalculatedEpoch, slot)
func needsUpdate*(
tracker: ActionTracker, state: ForkyHashedBeaconState, epoch: Epoch): bool =
# Using the attester dependent root here means we lock the action tracking to
# the dependent root for attestation duties and not block proposal -
# however, the risk of a proposer reordering in the last epoch is small
# and the action tracker is speculative in nature.
tracker.attesterDepRoot !=
state.dependent_root(if epoch > Epoch(0): epoch - 1 else: epoch)
func updateActions*(
tracker: var ActionTracker, epochRef: EpochRef) =
# Updates the schedule for upcoming attestation and proposal work
let
epoch = epochRef.epoch
tracker.attesterDepRoot = epochRef.shufflingRef.attester_dependent_root
tracker.lastCalculatedEpoch = epoch
let validatorIndices = toHashSet(toSeq(tracker.knownValidators.keys()))
# Update proposals
tracker.proposingSlots[epoch mod 2] = 0
for i, proposer in epochRef.beacon_proposers:
if proposer.isSome and proposer.get() in validatorIndices:
tracker.proposingSlots[epoch mod 2] =
tracker.proposingSlots[epoch mod 2] or (1'u32 shl i)
tracker.attestingSlots[epoch mod 2] = 0
# The relevant bitmaps are 32 bits each.
static: doAssert SLOTS_PER_EPOCH <= 32
for (committeeIndex, subnet_id, slot) in
get_committee_assignments(epochRef.shufflingRef, validatorIndices):
doAssert epoch(slot) == epoch
# Each get_committee_assignments() call here is on the next epoch. At any
# given time, only care about two epochs, the current and next epoch. So,
# after it is done for an epoch, [aS[epoch mod 2], aS[1 - (epoch mod 2)]]
# provides, sequentially, the current and next epochs' slot schedules. If
# get_committee_assignments() has not been called for the next epoch yet,
# typically because there hasn't been a block in the current epoch, there
# isn't valid information in aS[1 - (epoch mod 2)], and only slots within
# the current epoch can be known. Usually, this is not a major issue, but
# when there hasn't been a block substantially through an epoch, it might
# prove misleading to claim that there aren't attestations known, when it
# only might be known either way for 3 more slots. However, it's also not
# as important to attest if blocks aren't flowing as only attestations in
# blocks garner rewards.
tracker.attestingSlots[epoch mod 2] =
tracker.attestingSlots[epoch mod 2] or
(1'u32 shl (slot mod SLOTS_PER_EPOCH))
func init*(
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T: type ActionTracker, rng: ref HmacDrbgContext,
subscribeAllAttnets: bool): T =
T(
rng: rng,
subscribeAllAttnets: subscribeAllAttnets
)