misc memory and perf fixes (#1899)

* misc memory and perf fixes

* use EpochRef for attestation aggregation
* compress effective balances in memory (medalla unfinalized: 4gb ->
1gb)
* avoid hitting db when rewinding to head or clearance state
* avoid hitting db when blocks can be applied to in-memory state -
speeds up startup considerably
* avoid storing epochref in fork choice
* simplify and speed up beacon block creation flow - avoids state reload
thanks to head rewind optimization
* iterator-based committee and attestation participation help avoid lots
of small memory allocations throughout epoch transition (40% speedup on
epoch processing, for example during startup)

* add constant for threshold

beacon_chain/attestation_aggregation.nim

@@ -11,8 +11,7 @@ import
   std/[options, sequtils, sets],
   chronos, chronicles,
   ./spec/[
-    beaconstate, datatypes, crypto, digest, helpers, network, validator,
+    beaconstate, datatypes, crypto, digest, helpers, network, signatures],
-    signatures],
   ./block_pools/[spec_cache, chain_dag, quarantine, spec_cache],
   ./attestation_pool, ./beacon_node_types, ./ssz, ./time
 
@@ -29,26 +28,22 @@ func is_aggregator*(committee_len: uint64, slot_signature: ValidatorSig): bool =
   bytes_to_uint64(eth2digest(
     slot_signature.toRaw()).data.toOpenArray(0, 7)) mod modulo == 0
 
-func is_aggregator(state: BeaconState, slot: Slot, index: CommitteeIndex,
+func is_aggregator(epochRef: EpochRef, slot: Slot, index: CommitteeIndex,
-    slot_signature: ValidatorSig, cache: var StateCache): bool =
+    slot_signature: ValidatorSig): bool =
   let
-    committee_len = get_beacon_committee_len(state, slot, index, cache)
+    committee_len = get_beacon_committee_len(epochRef, slot, index)
   return is_aggregator(committee_len, slot_signature)
 
 proc aggregate_attestations*(
-    pool: AttestationPool, state: BeaconState, index: CommitteeIndex,
+    pool: AttestationPool, epochRef: EpochRef, slot: Slot, index: CommitteeIndex,
-    validatorIndex: ValidatorIndex, slot_signature: ValidatorSig,
+    validatorIndex: ValidatorIndex, slot_signature: ValidatorSig): Option[AggregateAndProof] =
-    cache: var StateCache): Option[AggregateAndProof] =
+  doAssert validatorIndex in get_beacon_committee(epochRef, slot, index)
-  let
+  doAssert index.uint64 < get_committee_count_per_slot(epochRef)
-    slot = state.slot
-
-  doAssert validatorIndex in get_beacon_committee(state, slot, index, cache)
-  doAssert index.uint64 < get_committee_count_per_slot(state, slot.epoch, cache)
 
   # TODO for testing purposes, refactor this into the condition check
   # and just calculation
   # https://github.com/ethereum/eth2.0-specs/blob/v1.0.0-rc.0/specs/phase0/validator.md#aggregation-selection
-  if not is_aggregator(state, slot, index, slot_signature, cache):
+  if not is_aggregator(epochRef, slot, index, slot_signature):
     return none(AggregateAndProof)
 
   let maybe_slot_attestation = getAggregatedAttestation(pool, slot, index)

beacon_chain/block_pools/block_pools_types.nim

@@ -148,7 +148,7 @@ type
     validator_key_store*: (Eth2Digest, ref seq[ValidatorPubKey])
 
     # balances, as used in fork choice
-    effective_balances*: seq[Gwei]
+    effective_balances_bytes*: seq[byte]
 
   BlockRef* = ref object
     ## Node in object graph guaranteed to lead back to tail block, and to have

beacon_chain/block_pools/chain_dag.nim

@@ -8,12 +8,9 @@
 {.push raises: [Defect].}
 
 import
-  # Standard libraries
+  std/[options, sequtils, tables, sets],
-  chronicles, options, sequtils, tables, sets,
+  metrics, snappy, chronicles,
-  # Status libraries
+  ../ssz/[ssz_serialization, merkleization], ../beacon_chain_db, ../extras,
-  metrics,
-  # Internals
-  ../ssz/merkleization, ../beacon_chain_db, ../extras,
   ../spec/[
     crypto, datatypes, digest, helpers, validator, state_transition,
     beaconstate],
@@ -143,12 +140,28 @@ proc init*(
       newClone(mapIt(state.validators.toSeq, it.pubkey)))
 
   # When fork choice runs, it will need the effective balance of the justified
-  # epoch - we pre-load the balances here to avoid rewinding the justified
+  # checkpoint - we pre-load the balances here to avoid rewinding the justified
-  # state later
+  # state later and compress them because not all checkpoints end up being used
-  epochRef.effective_balances = get_effective_balances(state)
+  # for fork choice - specially during long periods of non-finalization
+  proc snappyEncode(inp: openArray[byte]): seq[byte] =
+    try:
+      snappy.encode(inp)
+    except CatchableError as err:
+      raiseAssert err.msg
+
+  epochRef.effective_balances_bytes =
+    snappyEncode(SSZ.encode(
+      List[Gwei, Limit VALIDATOR_REGISTRY_LIMIT](get_effective_balances(state))))
 
   epochRef
 
+func effective_balances*(epochRef: EpochRef): seq[Gwei] =
+  try:
+    SSZ.decode(snappy.decode(epochRef.effective_balances_bytes, uint32.high),
+      List[Gwei, Limit VALIDATOR_REGISTRY_LIMIT]).toSeq()
+  except CatchableError as exc:
+    raiseAssert exc.msg
+
 func updateKeyStores*(epochRef: EpochRef, blck: BlockRef, finalized: BlockRef) =
   # Because key stores are additive lists, we can use a newer list whereever an
   # older list is expected - all indices in the new list will be valid for the
@@ -651,13 +664,55 @@ proc updateStateData*(
   # that the state has not been advanced past the desired block - if it has,
   # an earlier state must be loaded since there's no way to undo the slot
   # transitions
-  if state.blck == bs.blck and state.data.data.slot <= bs.slot:
-    # The block is the same and we're at an early enough slot - advance the
-    # state with empty slot processing until the slot is correct
-    dag.advanceSlots(state, bs.slot, save, cache)
 
-    return
+  var
+    ancestors: seq[BlockRef]
+    cur = bs
+    found = false
 
+  template canAdvance(state: StateData, bs: BlockSlot): bool =
+    # The block is the same and we're at an early enough slot - the state can
+    # be used to arrive at the desired blockslot
+    state.blck == bs.blck and state.data.data.slot <= bs.slot
+
+  # First, run a quick check if we can simply apply a few blocks to an in-memory
+  # state - any in-memory state will be faster than loading from database.
+  # The limit here how many blocks we apply is somewhat arbitrary but two full
+  # epochs (might be more slots if there are skips) seems like a good enough
+  # first guess.
+  # This happens in particular during startup where we replay blocks
+  # sequentially to grab their votes.
+  const RewindBlockThreshold = 64
+  while ancestors.len < RewindBlockThreshold:
+    if canAdvance(state, cur):
+      found = true
+      break
+
+    if canAdvance(dag.headState, cur):
+      assign(state, dag.headState)
+      found = true
+      break
+
+    if canAdvance(dag.clearanceState, cur):
+      assign(state, dag.clearanceState)
+      found = true
+      break
+
+    if cur.slot == cur.blck.slot:
+      # This is not an empty slot, so the block will need to be applied to
+      # eventually reach bs
+      ancestors.add(cur.blck)
+
+    if cur.blck.parent == nil:
+      break
+
+    # Moving slot by slot helps find states that were advanced with empty slots
+    cur = cur.parentOrSlot
+
+  # Let's see if we're within a few epochs of the state block - then we can
+  # simply replay blocks without loading the whole state
+
+  if not found:
     debug "UpdateStateData cache miss",
       bs, stateBlock = state.blck, stateSlot = state.data.data.slot
 
@@ -665,9 +720,9 @@ proc updateStateData*(
     # We'll now resort to loading the state from the database then reapplying
     # blocks until we reach the desired point in time.
 
-  var
-    ancestors: seq[BlockRef]
     cur = bs
+    ancestors.setLen(0)
+
     # Look for a state in the database and load it - as long as it cannot be
     # found, keep track of the blocks that are needed to reach it from the
     # state that eventually will be found
@@ -689,6 +744,8 @@ proc updateStateData*(
         # Moves back slot by slot, in case a state for an empty slot was saved
         cur = cur.parent
 
+    beacon_state_rewinds.inc()
+
   let
     startSlot {.used.} = state.data.data.slot # used in logs below
     startRoot {.used.} = state.data.root
@@ -705,16 +762,15 @@ proc updateStateData*(
   # ...and make sure to process empty slots as requested
   dag.advanceSlots(state, bs.slot, save, cache)
 
-  beacon_state_rewinds.inc()
+  trace "State updated",
-
-  trace "State reloaded from database",
     blocks = ancestors.len,
     slots = state.data.data.slot - startSlot,
     stateRoot = shortLog(state.data.root),
     stateSlot = state.data.data.slot,
     startRoot = shortLog(startRoot),
     startSlot,
-    blck = shortLog(bs)
+    blck = shortLog(bs),
+    found
 
 proc delState(dag: ChainDAGRef, bs: BlockSlot) =
   # Delete state state and mapping for a particular block+slot

beacon_chain/block_pools/spec_cache.nim

@@ -7,8 +7,9 @@
 
 import
   std/[algorithm, sequtils, sets],
+  chronicles,
   ../spec/[
-    beaconstate, crypto, datatypes, digest, helpers, presets, signatures,
+    crypto, datatypes, digest, helpers, presets, signatures,
     validator],
   ../extras,
   ./block_pools_types, ./chain_dag
@@ -21,6 +22,19 @@ func count_active_validators*(epochInfo: EpochRef): uint64 =
 func get_committee_count_per_slot*(epochInfo: EpochRef): uint64 =
   get_committee_count_per_slot(count_active_validators(epochInfo))
 
+# https://github.com/ethereum/eth2.0-specs/blob/v1.0.0-rc.0/specs/phase0/beacon-chain.md#get_beacon_committee
+iterator get_beacon_committee*(
+    epochRef: EpochRef, slot: Slot, index: CommitteeIndex): ValidatorIndex =
+  # Return the beacon committee at ``slot`` for ``index``.
+  let
+    committees_per_slot = get_committee_count_per_slot(epochRef)
+  for idx in compute_committee(
+    epochRef.shuffled_active_validator_indices,
+    (slot mod SLOTS_PER_EPOCH) * committees_per_slot +
+      index.uint64,
+    committees_per_slot * SLOTS_PER_EPOCH
+  ): yield idx
+
 # https://github.com/ethereum/eth2.0-specs/blob/v1.0.0-rc.0/specs/phase0/beacon-chain.md#get_beacon_committee
 func get_beacon_committee*(
     epochRef: EpochRef, slot: Slot, index: CommitteeIndex): seq[ValidatorIndex] =
@@ -34,14 +48,41 @@ func get_beacon_committee*(
     committees_per_slot * SLOTS_PER_EPOCH
   )
 
+# https://github.com/ethereum/eth2.0-specs/blob/v1.0.0-rc.0/specs/phase0/beacon-chain.md#get_beacon_committee
+func get_beacon_committee_len*(
+    epochRef: EpochRef, slot: Slot, index: CommitteeIndex): uint64 =
+  # Return the number of members in the beacon committee at ``slot`` for ``index``.
+  let
+    committees_per_slot = get_committee_count_per_slot(epochRef)
+
+  compute_committee_len(
+    count_active_validators(epochRef),
+    (slot mod SLOTS_PER_EPOCH) * committees_per_slot +
+      index.uint64,
+    committees_per_slot * SLOTS_PER_EPOCH
+  )
+
+# https://github.com/ethereum/eth2.0-specs/blob/v1.0.0-rc.0/specs/phase0/beacon-chain.md#get_attesting_indices
+iterator get_attesting_indices*(epochRef: EpochRef,
+                                data: AttestationData,
+                                bits: CommitteeValidatorsBits):
+                                  ValidatorIndex =
+  if bits.lenu64 != get_beacon_committee_len(epochRef, data.slot, data.index.CommitteeIndex):
+    trace "get_attesting_indices: inconsistent aggregation and committee length"
+  else:
+    var i = 0
+    for index in get_beacon_committee(epochRef, data.slot, data.index.CommitteeIndex):
+      if bits[i]:
+        yield index
+      inc i
+
 # https://github.com/ethereum/eth2.0-specs/blob/v1.0.0-rc.0/specs/phase0/beacon-chain.md#get_attesting_indices
 func get_attesting_indices*(epochRef: EpochRef,
                             data: AttestationData,
                             bits: CommitteeValidatorsBits):
                               HashSet[ValidatorIndex] =
-  get_attesting_indices(
+  for idx in get_attesting_indices(epochRef, data, bits):
-    bits,
+    result.incl(idx)
-    get_beacon_committee(epochRef, data.slot, data.index.CommitteeIndex))
 
 # https://github.com/ethereum/eth2.0-specs/blob/v1.0.0-rc.0/specs/phase0/beacon-chain.md#get_indexed_attestation
 func get_indexed_attestation*(epochRef: EpochRef, attestation: Attestation): IndexedAttestation =
@@ -59,20 +100,6 @@ func get_indexed_attestation*(epochRef: EpochRef, attestation: Attestation): Ind
     signature: attestation.signature
   )
 
-# https://github.com/ethereum/eth2.0-specs/blob/v1.0.0-rc.0/specs/phase0/beacon-chain.md#get_beacon_committee
-func get_beacon_committee_len*(
-    epochRef: EpochRef, slot: Slot, index: CommitteeIndex): uint64 =
-  # Return the number of members in the beacon committee at ``slot`` for ``index``.
-  let
-    committees_per_slot = get_committee_count_per_slot(epochRef)
-
-  compute_committee_len(
-    count_active_validators(epochRef),
-    (slot mod SLOTS_PER_EPOCH) * committees_per_slot +
-      index.uint64,
-    committees_per_slot * SLOTS_PER_EPOCH
-  )
-
 # https://github.com/ethereum/eth2.0-specs/blob/v1.0.0-rc.0/specs/phase0/validator.md#aggregation-selection
 func is_aggregator*(epochRef: EpochRef, slot: Slot, index: CommitteeIndex,
     slot_signature: ValidatorSig): bool =

beacon_chain/fork_choice/fork_choice.nim

@@ -71,10 +71,10 @@ proc init*(T: type ForkChoice,
     epoch = epochRef.epoch, blck = shortLog(blck)
 
   let
-    justified = BalanceCheckpoint(blck: blck, epochRef: epochRef)
+    justified = BalanceCheckpoint(blck: blck, epoch: epochRef.epoch, balances: epochRef.effective_balances)
     finalized = Checkpoint(root: blck.root, epoch: epochRef.epoch)
     best_justified = Checkpoint(
-      root: justified.blck.root, epoch: justified.epochRef.epoch)
+      root: justified.blck.root, epoch: justified.epoch)
 
   ForkChoice(
     backend: ForkChoiceBackend.init(
@@ -95,7 +95,6 @@ func extend[T](s: var seq[T], minLen: int) =
 proc compute_slots_since_epoch_start(slot: Slot): uint64 =
     slot - slot.epoch().compute_start_slot_at_epoch()
 
-
 proc on_tick(self: var Checkpoints, dag: ChainDAGRef, time: Slot): FcResult[void] =
   if self.time > time:
     return err(ForkChoiceError(kind: fcInconsistentTick))
@@ -104,15 +103,17 @@ proc on_tick(self: var Checkpoints, dag: ChainDAGRef, time: Slot): FcResult[void
   self.time = time
 
   if newEpoch and
-      self.best_justified.epoch > self.justified.epochRef.epoch:
+      self.best_justified.epoch > self.justified.epoch:
     let blck = dag.getRef(self.best_justified.root)
     if blck.isNil:
       return err(ForkChoiceError(
         kind: fcJustifiedNodeUnknown, block_root: self.best_justified.root))
 
+    let epochRef = dag.getEpochRef(blck, self.best_justified.epoch)
     self.justified = BalanceCheckpoint(
       blck: blck,
-      epochRef: dag.getEpochRef(blck, self.best_justified.epoch))
+      epoch: epochRef.epoch,
+      balances: epochRef.effective_balances)
   ok()
 
 proc process_attestation_queue(self: var ForkChoice) {.gcsafe.}
@@ -202,18 +203,15 @@ proc should_update_justified_checkpoint(
     return ok(true)
 
   let
-    justified_slot = compute_start_slot_at_epoch(self.justified.epochRef.epoch)
+    justified_slot = compute_start_slot_at_epoch(self.justified.epoch)
-
+    new_justified_checkpoint = epochRef.current_justified_checkpoint
-  let new_justified_checkpoint = epochRef.current_justified_checkpoint;
+    justified_blck = dag.getRef(new_justified_checkpoint.root)
-
-  let justified_blck = dag.getRef(new_justified_checkpoint.root)
 
   if justified_blck.isNil:
     return err(ForkChoiceError(
       kind: fcJustifiedNodeUnknown, block_root: new_justified_checkpoint.root))
 
-  let justified_ancestor =
+  let justified_ancestor = justified_blck.atSlot(justified_slot)
-    justified_blck.atSlot(justified_slot)
 
   if justified_ancestor.blck.root != self.justified.blck.root:
     return ok(false)
@@ -231,38 +229,44 @@ proc process_state(self: var Checkpoints,
   trace "Processing epoch",
     epoch = epochRef.epoch,
     state_justified_epoch = state_justified_epoch,
-    current_justified = self.justified.epochRef.epoch,
+    current_justified = self.justified.epoch,
     state_finalized_epoch = state_finalized_epoch,
     current_finalized = self.finalized.epoch
 
-  if state_justified_epoch > self.justified.epochRef.epoch:
+  if state_justified_epoch > self.justified.epoch:
     if state_justified_epoch > self.best_justified.epoch:
       self.best_justified = epochRef.current_justified_checkpoint
 
     if ? should_update_justified_checkpoint(self, dag, epochRef):
-      let justifiedBlck = blck.atEpochStart(state_justified_epoch)
+      let
+        justifiedBlck = blck.atEpochStart(state_justified_epoch)
+        justifiedEpoch = dag.getEpochRef(justifiedBlck.blck, state_justified_epoch)
 
       self.justified =
         BalanceCheckpoint(
           blck: justifiedBlck.blck,
-          epochRef: dag.getEpochRef(justifiedBlck.blck, state_justified_epoch))
+          epoch: justifiedEpoch.epoch,
+          balances: justifiedEpoch.effective_balances)
 
   if state_finalized_epoch > self.finalized.epoch:
     self.finalized = epochRef.finalized_checkpoint
 
-    if self.justified.epochRef.epoch != state_justified_epoch or
+    if self.justified.epoch != state_justified_epoch or
       self.justified.blck.root != epochRef.current_justified_checkpoint.root:
 
-      if (state_justified_epoch > self.justified.epochRef.epoch) or
+      if (state_justified_epoch > self.justified.epoch) or
           (self.justified.blck.atEpochStart(self.finalized.epoch).blck.root !=
             self.finalized.root):
 
-        let justifiedBlck = blck.atEpochStart(state_justified_epoch)
+        let
+          justifiedBlck = blck.atEpochStart(state_justified_epoch)
+          justifiedEpoch = dag.getEpochRef(justifiedBlck.blck, state_justified_epoch)
 
         self.justified =
           BalanceCheckpoint(
             blck: justifiedBlck.blck,
-            epochRef: dag.getEpochRef(justifiedBlck.blck, state_justified_epoch))
+            epoch: justifiedEpoch.epoch,
+            balances: justifiedEpoch.effective_balances)
   ok()
 
 proc process_block*(self: var ForkChoiceBackend,
@@ -360,10 +364,10 @@ proc get_head*(self: var ForkChoice,
   ? self.update_time(dag, wallSlot)
 
   self.backend.find_head(
-    self.checkpoints.justified.epochRef.epoch,
+    self.checkpoints.justified.epoch,
     self.checkpoints.justified.blck.root,
     self.checkpoints.finalized.epoch,
-    self.checkpoints.justified.epochRef.effective_balances,
+    self.checkpoints.justified.balances,
   )
 
 func prune*(

beacon_chain/fork_choice/fork_choice_types.nim

@@ -135,7 +135,8 @@ type
 
   BalanceCheckpoint* = object
     blck*: BlockRef
-    epochRef*: EpochRef
+    epoch*: Epoch
+    balances*: seq[Gwei]
 
   Checkpoints* = object
     time*: Slot

beacon_chain/spec/beaconstate.nim

@@ -460,9 +460,14 @@ proc is_valid_indexed_attestation*(
   ok()
 
 # https://github.com/ethereum/eth2.0-specs/blob/v1.0.0-rc.0/specs/phase0/beacon-chain.md#get_attesting_indices
-func get_attesting_indices*(bits: CommitteeValidatorsBits,
+iterator get_attesting_indices*(bits: CommitteeValidatorsBits,
                                 committee: openArray[ValidatorIndex]):
-                            HashSet[ValidatorIndex] =
+                                  ValidatorIndex =
+  if bits.len == committee.len:
+    for i, index in committee:
+      if bits[i]:
+        yield index
+  else:
     # This shouldn't happen if one begins with a valid BeaconState and applies
     # valid updates, but one can construct a BeaconState where it does. Do not
     # do anything here since the PendingAttestation wouldn't have made it past
@@ -470,13 +475,28 @@ func get_attesting_indices*(bits: CommitteeValidatorsBits,
     # which checks len(attestation.aggregation_bits) == len(committee) that in
     # nimbus-eth2 lives in check_attestation(...).
     # Addresses https://github.com/status-im/nimbus-eth2/issues/922
-  if bits.len != committee.len:
-    trace "get_attesting_indices: inconsistent aggregation and committee length"
-    return
 
-  for i, index in committee:
+    trace "get_attesting_indices: inconsistent aggregation and committee length"
+
+func get_attesting_indices*(bits: CommitteeValidatorsBits,
+                            committee: openArray[ValidatorIndex]):
+                            HashSet[ValidatorIndex] =
+  for idx in get_attesting_indices(bits, committee):
+    result.incl idx
+
+# https://github.com/ethereum/eth2.0-specs/blob/v1.0.0-rc.0/specs/phase0/beacon-chain.md#get_attesting_indices
+iterator get_attesting_indices*(state: BeaconState,
+                                data: AttestationData,
+                                bits: CommitteeValidatorsBits,
+                                cache: var StateCache): ValidatorIndex =
+  if bits.lenu64 != get_beacon_committee_len(state, data.slot, data.index.CommitteeIndex, cache):
+    trace "get_attesting_indices: inconsistent aggregation and committee length"
+  else:
+    var i = 0
+    for index in get_beacon_committee(state, data.slot, data.index.CommitteeIndex, cache):
       if bits[i]:
-      result.incl index
+        yield index
+      inc i
 
 # https://github.com/ethereum/eth2.0-specs/blob/v1.0.0-rc.0/specs/phase0/beacon-chain.md#get_attesting_indices
 func get_attesting_indices*(state: BeaconState,
@@ -485,9 +505,8 @@ func get_attesting_indices*(state: BeaconState,
                             cache: var StateCache):
                             HashSet[ValidatorIndex] =
   # Return the set of attesting indices corresponding to ``data`` and ``bits``.
-  get_attesting_indices(
+  for index in get_attesting_indices(state, data, bits, cache):
-    bits,
+    result.incl index
-    get_beacon_committee(state, data.slot, data.index.CommitteeIndex, cache))
 
 # https://github.com/ethereum/eth2.0-specs/blob/v1.0.0-rc.0/specs/phase0/beacon-chain.md#get_indexed_attestation
 func get_indexed_attestation(state: BeaconState, attestation: Attestation,

beacon_chain/spec/state_transition_helpers.nim

@@ -22,16 +22,15 @@ func get_attesting_indices*(
     cache: var StateCache): HashSet[ValidatorIndex] =
   # This is part of get_unslashed_attesting_indices(...) in spec.
   # Exported bceause of external trace-level chronicles logging.
-  result = initHashSet[ValidatorIndex]()
   for a in attestations:
-    result.incl get_attesting_indices(
+    for idx in get_attesting_indices(
-      state, a.data, a.aggregation_bits, cache)
+        state, a.data, a.aggregation_bits, cache):
+      result.incl idx
 
 # https://github.com/ethereum/eth2.0-specs/blob/v1.0.0-rc.0/specs/phase0/beacon-chain.md#helper-functions-1
 func get_unslashed_attesting_indices*(
     state: BeaconState, attestations: openArray[PendingAttestation],
     cache: var StateCache): HashSet[ValidatorIndex] =
-  result = initHashSet[ValidatorIndex]()
   for a in attestations:
     for idx in get_attesting_indices(
         state, a.data, a.aggregation_bits, cache):

beacon_chain/spec/validator.nim

@@ -200,6 +200,13 @@ func compute_committee_slice*(
 
   start.int..(endIdx.int - 1)
 
+iterator compute_committee*(shuffled_indices: seq[ValidatorIndex],
+    index: uint64, count: uint64): ValidatorIndex =
+  let
+    slice = compute_committee_slice(shuffled_indices.lenu64, index, count)
+  for i in slice:
+    yield shuffled_indices[i]
+
 func compute_committee*(shuffled_indices: seq[ValidatorIndex],
     index: uint64, count: uint64): seq[ValidatorIndex] =
   ## Return the committee corresponding to ``indices``, ``seed``, ``index``,
@@ -224,6 +231,20 @@ func compute_committee_len*(
   (slice.b - slice.a + 1).uint64
 
 # https://github.com/ethereum/eth2.0-specs/blob/v1.0.0-rc.0/specs/phase0/beacon-chain.md#get_beacon_committee
+iterator get_beacon_committee*(
+    state: BeaconState, slot: Slot, index: CommitteeIndex,
+    cache: var StateCache): ValidatorIndex =
+  ## Return the beacon committee at ``slot`` for ``index``.
+  let
+    epoch = compute_epoch_at_slot(slot)
+    committees_per_slot = get_committee_count_per_slot(state, epoch, cache)
+  for idx in compute_committee(
+    cache.get_shuffled_active_validator_indices(state, epoch),
+    (slot mod SLOTS_PER_EPOCH) * committees_per_slot +
+      index.uint64,
+    committees_per_slot * SLOTS_PER_EPOCH
+  ): yield idx
+
 func get_beacon_committee*(
     state: BeaconState, slot: Slot, index: CommitteeIndex,
     cache: var StateCache): seq[ValidatorIndex] =

beacon_chain/validator_api.nim

@@ -321,13 +321,11 @@ proc installValidatorApiHandlers*(rpcServer: RpcServer, node: BeaconNode) =
     let proposer = node.chainDag.getProposer(head, slot)
     if proposer.isNone():
       raise newException(CatchableError, "could not retrieve block for slot: " & $slot)
-    let valInfo = ValidatorInfoForMakeBeaconBlock(kind: viRandao_reveal,
+    let message = makeBeaconBlockForHeadAndSlot(
-                                                  randao_reveal: randao_reveal)
+      node, randao_reveal, proposer.get()[0], graffiti, head, slot)
-    let res = await makeBeaconBlockForHeadAndSlot(
+    if message.isNone():
-      node, valInfo, proposer.get()[0], graffiti, head, slot)
-    if res.message.isNone():
       raise newException(CatchableError, "could not retrieve block for slot: " & $slot)
-    return res.message.get()
+    return message.get()
 
   rpcServer.rpc("post_v1_validator_block") do (body: SignedBeaconBlock) -> bool:
     debug "post_v1_validator_block",

beacon_chain/validator_duties.nim

@@ -18,7 +18,7 @@ import
   eth/[keys, async_utils], eth/p2p/discoveryv5/[protocol, enr],
 
   # Local modules
-  spec/[datatypes, digest, crypto, helpers, validator, network, signatures],
+  spec/[datatypes, digest, crypto, helpers, network, signatures],
   spec/state_transition,
   conf, time, validator_pool,
   attestation_pool, exit_pool, block_pools/[spec_cache, chain_dag, clearance],
@@ -176,46 +176,20 @@ proc createAndSendAttestation(node: BeaconNode,
     validator = shortLog(validator),
     indexInCommittee = indexInCommittee
 
-type
-  ValidatorInfoForMakeBeaconBlockKind* = enum
-    viValidator
-    viRandao_reveal
-  ValidatorInfoForMakeBeaconBlock* = object
-    case kind*: ValidatorInfoForMakeBeaconBlockKind
-    of viValidator: validator*: AttachedValidator
-    of viRandao_reveal: randao_reveal*: ValidatorSig
-
 proc makeBeaconBlockForHeadAndSlot*(node: BeaconNode,
-                                    val_info: ValidatorInfoForMakeBeaconBlock,
+                                    randao_reveal: ValidatorSig,
                                     validator_index: ValidatorIndex,
                                     graffiti: GraffitiBytes,
                                     head: BlockRef,
-                                    slot: Slot):
+                                    slot: Slot): Option[BeaconBlock] =
-    Future[tuple[message: Option[BeaconBlock], fork: Fork,
+  # Advance state to the slot that we're proposing for
-                 genesis_validators_root: Eth2Digest]] {.async.} =
+  node.chainDag.withState(node.chainDag.tmpState, head.atSlot(slot)):
-  # Advance state to the slot that we're proposing for - this is the equivalent
-  # of running `process_slots` up to the slot of the new block.
-  node.chainDag.withState(
-      node.chainDag.tmpState, head.atSlot(slot)):
     let (eth1data, deposits) =
       if node.mainchainMonitor.isNil:
         (state.eth1_data, newSeq[Deposit]())
       else:
         node.mainchainMonitor.getBlockProposalData(state)
 
-    # TODO perhaps just making the enclosing function accept 2 different types at the
-    # same time and doing some compile-time branching logic is cleaner (without the
-    # need for the discriminated union)... but we need the `state` from `withState`
-    # in order to get the fork/root for the specific head/slot for the randao_reveal
-    # and it's causing problems when the function becomes a generic for 2 types...
-    proc getRandaoReveal(val_info: ValidatorInfoForMakeBeaconBlock):
-        Future[ValidatorSig] {.async.} =
-      if val_info.kind == viValidator:
-        return await val_info.validator.genRandaoReveal(
-          state.fork, state.genesis_validators_root, slot)
-      elif val_info.kind == viRandao_reveal:
-        return val_info.randao_reveal
-
     let
       poolPtr = unsafeAddr node.chainDag # safe because restore is short-lived
 
@@ -226,12 +200,12 @@ proc makeBeaconBlockForHeadAndSlot*(node: BeaconNode,
       doAssert v.addr == addr poolPtr.tmpState.data
       assign(poolPtr.tmpState, poolPtr.headState)
 
-    let message = makeBeaconBlock(
+    makeBeaconBlock(
       node.config.runtimePreset,
       hashedState,
       validator_index,
       head.root,
-      await getRandaoReveal(val_info),
+      randao_reveal,
       eth1data,
       graffiti,
       node.attestationPool[].getAttestationsForBlock(state, cache),
@@ -242,15 +216,6 @@ proc makeBeaconBlockForHeadAndSlot*(node: BeaconNode,
       restore,
       cache)
 
-    if message.isSome():
-      # TODO this restore is needed because otherwise tmpState will be internally
-      #      inconsistent - it's blck will not be pointing to the block that
-      #      created this state - we have to reset it here before `await` to avoid
-      #      races.
-      restore(poolPtr.tmpState.data)
-
-    return (message, state.fork, state.genesis_validators_root)
-
 proc proposeSignedBlock*(node: BeaconNode,
                          head: BlockRef,
                          validator: AttachedValidator,
@@ -310,27 +275,33 @@ proc proposeBlock(node: BeaconNode,
       existingProposal = notSlashable.error
     return head
 
-  let valInfo = ValidatorInfoForMakeBeaconBlock(kind: viValidator, validator: validator)
+  let
-  let beaconBlockTuple = await makeBeaconBlockForHeadAndSlot(
+    fork = node.chainDag.headState.data.data.fork
-    node, valInfo, validator_index, node.graffitiBytes, head, slot)
+    genesis_validators_root =
-  if not beaconBlockTuple.message.isSome():
+      node.chainDag.headState.data.data.genesis_validators_root
+  let
+    randao = await validator.genRandaoReveal(
+      fork, genesis_validators_root, slot)
+    message = makeBeaconBlockForHeadAndSlot(
+      node, randao, validator_index, node.graffitiBytes, head, slot)
+  if not message.isSome():
     return head # already logged elsewhere!
   var
     newBlock = SignedBeaconBlock(
-      message: beaconBlockTuple.message.get()
+      message: message.get()
     )
 
   newBlock.root = hash_tree_root(newBlock.message)
 
   # TODO: recomputed in block proposal
   let signing_root = compute_block_root(
-    beaconBlockTuple.fork, beaconBlockTuple.genesis_validators_root, slot, newBlock.root)
+    fork, genesis_validators_root, slot, newBlock.root)
   node.attachedValidators
     .slashingProtection
     .registerBlock(validator.pubkey, slot, signing_root)
 
   newBlock.signature = await validator.signBlockProposal(
-    beaconBlockTuple.fork, beaconBlockTuple.genesis_validators_root, slot, newBlock.root)
+    fork, genesis_validators_root, slot, newBlock.root)
 
   return await node.proposeSignedBlock(head, validator, newBlock)
 
@@ -458,11 +429,13 @@ proc broadcastAggregatedAttestations(
   # way to organize this. Then the private key for that validator should be
   # the corresponding one -- whatver they are, they match.
 
-  let bs = BlockSlot(blck: aggregationHead, slot: aggregationSlot)
-  node.chainDag.withState(node.chainDag.tmpState, bs):
   let
-      committees_per_slot =
+    bs = BlockSlot(blck: aggregationHead, slot: aggregationSlot)
-        get_committee_count_per_slot(state, aggregationSlot.epoch, cache)
+    epochRef = node.chainDag.getEpochRef(aggregationHead, aggregationSlot.epoch)
+    fork = node.chainDag.headState.data.data.fork
+    genesis_validators_root =
+      node.chainDag.headState.data.data.genesis_validators_root
+    committees_per_slot = get_committee_count_per_slot(epochRef)
 
   var
     slotSigs: seq[Future[ValidatorSig]] = @[]
@@ -472,31 +445,30 @@ proc broadcastAggregatedAttestations(
 
   for committee_index in 0'u64..<committees_per_slot:
     let committee = get_beacon_committee(
-        state, aggregationSlot, committee_index.CommitteeIndex, cache)
+      epochRef, aggregationSlot, committee_index.CommitteeIndex)
 
     for index_in_committee, validatorIdx in committee:
-        let validator = node.getAttachedValidator(state, validatorIdx)
+      let validator = node.getAttachedValidator(epochRef, validatorIdx)
       if validator != nil:
         # the validator index and private key pair.
-          slotSigs.add getSlotSig(validator, state.fork,
+        slotSigs.add getSlotSig(validator, fork,
-            state.genesis_validators_root, state.slot)
+          genesis_validators_root, aggregationSlot)
         slotSigsData.add (committee_index, validatorIdx, validator)
 
   await allFutures(slotSigs)
 
   for curr in zip(slotSigsData, slotSigs):
     let aggregateAndProof =
-        aggregate_attestations(node.attestationPool[], state,
+      aggregate_attestations(node.attestationPool[], epochRef, aggregationSlot,
                              curr[0].committee_index.CommitteeIndex,
                              curr[0].validator_idx,
-                               curr[1].read, cache)
+                             curr[1].read)
 
     # Don't broadcast when, e.g., this node isn't aggregator
     # TODO verify there is only one isSome() with test.
     if aggregateAndProof.isSome:
       let sig = await signAggregateAndProof(curr[0].v,
-          aggregateAndProof.get, state.fork,
+        aggregateAndProof.get, fork, genesis_validators_root)
-          state.genesis_validators_root)
       var signedAP = SignedAggregateAndProof(
         message: aggregateAndProof.get,
         signature: sig)