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nimbus-eth2/beacon_chain/block_pool.nim

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import
bitops, chronicles, options, tables,
ssz, beacon_chain_db, state_transition, extras,
beacon_node_types, metrics,
spec/[crypto, datatypes, digest, helpers]
declareCounter beacon_reorgs_total, "Total occurrences of reorganizations of the chain" # On fork choice
logScope: topics = "blkpool"
proc updateStateData*(
pool: BlockPool, state: var StateData, bs: BlockSlot) {.gcsafe.}
proc add*(
pool: var BlockPool, blockRoot: Eth2Digest,
signedBlock: SignedBeaconBlock): BlockRef {.gcsafe.}
template withState*(
pool: BlockPool, cache: var StateData, blockSlot: BlockSlot, body: untyped): untyped =
## Helper template that updates state to a particular BlockSlot - usage of
## cache is unsafe outside of block.
## TODO async transformations will lead to a race where cache gets updated
## while waiting for future to complete - catch this here somehow?
updateStateData(pool, cache, blockSlot)
template hashedState(): HashedBeaconState {.inject, used.} = cache.data
template state(): BeaconState {.inject, used.} = cache.data.data
template blck(): BlockRef {.inject, used.} = cache.blck
template root(): Eth2Digest {.inject, used.} = cache.data.root
body
func parent*(bs: BlockSlot): BlockSlot =
BlockSlot(
blck: if bs.slot > bs.blck.slot: bs.blck else: bs.blck.parent,
slot: bs.slot - 1
)
func link(parent, child: BlockRef) =
doAssert (not (parent.root == Eth2Digest() or child.root == Eth2Digest())),
"blocks missing root!"
doAssert parent.root != child.root, "self-references not allowed"
child.parent = parent
parent.children.add(child)
func isAncestorOf*(a, b: BlockRef): bool =
var b = b
var depth = 0
const maxDepth = (100'i64 * 365 * 24 * 60 * 60 div SECONDS_PER_SLOT.int)
while true:
if a == b: return true
# for now, use an assert for block chain length since a chain this long
# indicates a circular reference here..
doAssert depth < maxDepth
depth += 1
if a.slot >= b.slot or b.parent.isNil:
return false
doAssert b.slot > b.parent.slot
b = b.parent
func getAncestor*(blck: BlockRef, slot: Slot): BlockRef =
var blck = blck
var depth = 0
const maxDepth = (100'i64 * 365 * 24 * 60 * 60 div SECONDS_PER_SLOT.int)
while true:
if blck.slot == slot:
return blck
if blck.slot < slot:
return nil
if blck.parent == nil:
return nil
doAssert depth < maxDepth
depth += 1
blck = blck.parent
func init*(T: type BlockRef, root: Eth2Digest, slot: Slot): BlockRef =
BlockRef(
root: root,
slot: slot
)
func init*(T: type BlockRef, root: Eth2Digest, blck: BeaconBlock): BlockRef =
BlockRef.init(root, blck.slot)
func findAncestorBySlot*(blck: BlockRef, slot: Slot): BlockSlot =
## Find the first ancestor that has a slot number less than or equal to `slot`
doAssert(not blck.isNil)
var ret = blck
while ret.parent != nil and ret.slot > slot:
ret = ret.parent
BlockSlot(blck: ret, slot: slot)
proc init*(T: type BlockPool, db: BeaconChainDB): BlockPool =
# TODO we require that the db contains both a head and a tail block -
# asserting here doesn't seem like the right way to go about it however..
let
tailBlockRoot = db.getTailBlock()
headBlockRoot = db.getHeadBlock()
doAssert tailBlockRoot.isSome(), "Missing tail block, database corrupt?"
doAssert headBlockRoot.isSome(), "Missing head block, database corrupt?"
let
tailRoot = tailBlockRoot.get()
tailBlock = db.getBlock(tailRoot).get()
tailRef = BlockRef.init(tailRoot, tailBlock.message)
headRoot = headBlockRoot.get()
var
blocks = {tailRef.root: tailRef}.toTable()
latestStateRoot = Option[Eth2Digest]()
headRef: BlockRef
if headRoot != tailRoot:
var curRef: BlockRef
for root, blck in db.getAncestors(headRoot):
if root == tailRef.root:
doAssert(not curRef.isNil)
link(tailRef, curRef)
curRef = curRef.parent
break
let newRef = BlockRef.init(root, blck.message)
if curRef == nil:
curRef = newRef
headRef = newRef
else:
link(newRef, curRef)
curRef = curRef.parent
blocks[curRef.root] = curRef
trace "Populating block pool", key = curRef.root, val = curRef
if latestStateRoot.isNone() and db.containsState(blck.message.state_root):
latestStateRoot = some(blck.message.state_root)
doAssert curRef == tailRef,
"head block does not lead to tail, database corrupt?"
else:
headRef = tailRef
var blocksBySlot = initTable[Slot, seq[BlockRef]]()
for _, b in tables.pairs(blocks):
let slot = db.getBlock(b.root).get().message.slot
blocksBySlot.mgetOrPut(slot, @[]).add(b)
# TODO can't do straight init because in mainnet config, there are too
# many live beaconstates on the stack...
var tmpState = new Option[BeaconState]
let
# The head state is necessary to find out what we considered to be the
# finalized epoch last time we saved something.
headStateRoot =
if latestStateRoot.isSome():
latestStateRoot.get()
else:
db.getBlock(tailRef.root).get().message.state_root
# TODO right now, because we save a state at every epoch, this *should*
# be the latest justified state or newer, meaning it's enough for
# establishing what we consider to be the finalized head. This logic
# will need revisiting however
tmpState[] = db.getState(headStateRoot)
let
finalizedHead =
headRef.findAncestorBySlot(
tmpState[].get().finalized_checkpoint.epoch.compute_start_slot_at_epoch())
justifiedSlot =
tmpState[].get().current_justified_checkpoint.epoch.compute_start_slot_at_epoch()
justifiedHead = headRef.findAncestorBySlot(justifiedSlot)
head = Head(blck: headRef, justified: justifiedHead)
justifiedBlock = db.getBlock(justifiedHead.blck.root).get()
justifiedStateRoot = justifiedBlock.message.state_root
doAssert justifiedHead.slot >= finalizedHead.slot,
"justified head comes before finalized head - database corrupt?"
debug "Block pool initialized",
head = head.blck, finalizedHead, tail = tailRef,
totalBlocks = blocks.len, totalKnownSlots = blocksBySlot.len
let res = BlockPool(
pending: initTable[Eth2Digest, SignedBeaconBlock](),
missing: initTable[Eth2Digest, MissingBlock](),
blocks: blocks,
blocksBySlot: blocksBySlot,
tail: tailRef,
head: head,
finalizedHead: finalizedHead,
db: db,
heads: @[head],
)
res.headState = StateData(
data: HashedBeaconState(data: tmpState[].get(), root: headStateRoot),
blck: headRef)
res.tmpState = res.headState
tmpState[] = db.getState(justifiedStateRoot)
res.justifiedState = StateData(
data: HashedBeaconState(data: tmpState[].get(), root: justifiedStateRoot),
blck: justifiedHead.blck)
res
proc addSlotMapping(pool: BlockPool, br: BlockRef) =
proc addIfMissing(s: var seq[BlockRef], v: BlockRef) =
if v notin s:
s.add(v)
pool.blocksBySlot.mgetOrPut(br.slot, @[]).addIfMissing(br)
proc delSlotMapping(pool: BlockPool, br: BlockRef) =
var blks = pool.blocksBySlot.getOrDefault(br.slot)
if blks.len != 0:
let i = blks.find(br)
if i >= 0: blks.del(i)
if blks.len == 0:
pool.blocksBySlot.del(br.slot)
else:
pool.blocksBySlot[br.slot] = blks
proc addResolvedBlock(
pool: var BlockPool, state: var StateData, blockRoot: Eth2Digest,
signedBlock: SignedBeaconBlock, parent: BlockRef): BlockRef =
logScope: pcs = "block_resolution"
let blockRef = BlockRef.init(blockRoot, signedBlock.message)
link(parent, blockRef)
pool.blocks[blockRoot] = blockRef
trace "Populating block pool", key = blockRoot, val = blockRef
pool.addSlotMapping(blockRef)
# Resolved blocks should be stored in database
pool.db.putBlock(blockRoot, signedBlock)
# TODO this is a bit ugly - we update state.data outside of this function then
# set the rest here - need a blockRef to update it. Clean this up -
# hopefully it won't be necessary by the time hash caching and the rest
# is done..
doAssert state.data.data.slot == blockRef.slot
state.blck = blockRef
# This block *might* have caused a justification - make sure we stow away
# that information:
let justifiedSlot =
state.data.data.current_justified_checkpoint.epoch.compute_start_slot_at_epoch()
var foundHead: Option[Head]
for head in pool.heads.mitems():
if head.blck.isAncestorOf(blockRef):
if head.justified.slot != justifiedSlot:
head.justified = blockRef.findAncestorBySlot(justifiedSlot)
head.blck = blockRef
foundHead = some(head)
break
if foundHead.isNone():
foundHead = some(Head(
blck: blockRef,
justified: blockRef.findAncestorBySlot(justifiedSlot)))
pool.heads.add(foundHead.get())
info "Block resolved",
blck = shortLog(signedBlock.message),
blockRoot = shortLog(blockRoot),
justifiedRoot = shortLog(foundHead.get().justified.blck.root),
justifiedSlot = shortLog(foundHead.get().justified.slot),
cat = "filtering"
# Now that we have the new block, we should see if any of the previously
# unresolved blocks magically become resolved
# TODO there are more efficient ways of doing this that don't risk
# running out of stack etc
# TODO This code is convoluted because when there are more than ~1.5k
# blocks being synced, there's a stack overflow as `add` gets called
# for the whole chain of blocks. Instead we use this ugly field in `pool`
# which could be avoided by refactoring the code
if not pool.inAdd:
pool.inAdd = true
defer: pool.inAdd = false
var keepGoing = true
while keepGoing:
let retries = pool.pending
for k, v in retries:
discard pool.add(k, v)
# Keep going for as long as the pending pool is shrinking
# TODO inefficient! so what?
keepGoing = pool.pending.len < retries.len
blockRef
proc add*(
pool: var BlockPool, blockRoot: Eth2Digest,
signedBlock: SignedBeaconBlock): BlockRef {.gcsafe.} =
## return the block, if resolved...
## the state parameter may be updated to include the given block, if
## everything checks out
# TODO reevaluate passing the state in like this
let blck = signedBlock.message
doAssert blockRoot == hash_tree_root(blck)
logScope: pcs = "block_addition"
# Already seen this block??
if blockRoot in pool.blocks:
debug "Block already exists",
blck = shortLog(blck),
blockRoot = shortLog(blockRoot),
cat = "filtering"
return pool.blocks[blockRoot]
pool.missing.del(blockRoot)
# If the block we get is older than what we finalized already, we drop it.
# One way this can happen is that we start resolving a block and finalization
# happens in the meantime - the block we requested will then be stale
# by the time it gets here.
if blck.slot <= pool.finalizedHead.slot:
debug "Old block, dropping",
blck = shortLog(blck),
tailSlot = shortLog(pool.tail.slot),
blockRoot = shortLog(blockRoot),
cat = "filtering"
return
let parent = pool.blocks.getOrDefault(blck.parent_root)
if parent != nil:
if parent.slot >= blck.slot:
# TODO Malicious block? inform peer pool?
notice "Invalid block slot",
blck = shortLog(blck),
blockRoot = shortLog(blockRoot),
parentRoot = shortLog(parent.root),
parentSlot = shortLog(parent.slot)
return
# The block might have been in either of these - we don't want any more
# work done on its behalf
pool.pending.del(blockRoot)
# The block is resolved, now it's time to validate it to ensure that the
# blocks we add to the database are clean for the given state
# TODO if the block is from the future, we should not be resolving it (yet),
# but maybe we should use it as a hint that our clock is wrong?
updateStateData(pool, pool.tmpState, BlockSlot(blck: parent, slot: blck.slot - 1))
if not state_transition(pool.tmpState.data, blck, {}):
# TODO find a better way to log all this block data
notice "Invalid block",
blck = shortLog(blck),
blockRoot = shortLog(blockRoot),
cat = "filtering"
return
# Careful, pool.tmpState is now partially inconsistent and will be updated
# inside addResolvedBlock
return pool.addResolvedBlock(pool.tmpState, blockRoot, signedBlock, parent)
# TODO already checked hash though? main reason to keep this is because
# the pending pool calls this function back later in a loop, so as long
# as pool.add(...) requires a SignedBeaconBlock, easier to keep them in
# pending too.
pool.pending[blockRoot] = signedBlock
# TODO possibly, it makes sense to check the database - that would allow sync
# to simply fill up the database with random blocks the other clients
# think are useful - but, it would also risk filling the database with
# junk that's not part of the block graph
if blck.parent_root in pool.missing or
blck.parent_root in pool.pending:
return
# This is an unresolved block - put its parent on the missing list for now...
# TODO if we receive spam blocks, one heurestic to implement might be to wait
# for a couple of attestations to appear before fetching parents - this
# would help prevent using up network resources for spam - this serves
# two purposes: one is that attestations are likely to appear for the
# block only if it's valid / not spam - the other is that malicious
# validators that are not proposers can sign invalid blocks and send
# them out without penalty - but signing invalid attestations carries
# a risk of being slashed, making attestations a more valuable spam
# filter.
# TODO when we receive the block, we don't know how many others we're missing
# from that branch, so right now, we'll just do a blind guess
debug "Unresolved block (parent missing)",
blck = shortLog(blck),
blockRoot = shortLog(blockRoot),
cat = "filtering"
let parentSlot = blck.slot - 1
pool.missing[blck.parent_root] = MissingBlock(
slots:
# The block is at least two slots ahead - try to grab whole history
if parentSlot > pool.head.blck.slot:
parentSlot - pool.head.blck.slot
else:
# It's a sibling block from a branch that we're missing - fetch one
# epoch at a time
max(1.uint64, SLOTS_PER_EPOCH.uint64 -
(parentSlot.uint64 mod SLOTS_PER_EPOCH.uint64))
)
func getRef*(pool: BlockPool, root: Eth2Digest): BlockRef =
## Retrieve a resolved block reference, if available
pool.blocks.getOrDefault(root, nil)
proc getBlockRange*(pool: BlockPool, headBlock: Eth2Digest,
startSlot: Slot, skipStep: Natural,
output: var openarray[BlockRef]): Natural =
## This function populates an `output` buffer of blocks
## with a range starting from `startSlot` and skipping
## every `skipTest` number of blocks.
##
## Please note that the function may not necessarily
## populate the entire buffer. The values will be written
## in a way such that the last block is placed at the end
## of the buffer while the first indices of the buffer
## may remain unwritten.
##
## The result value of the function will be the index of
## the first block in the resulting buffer. If no values
## were written to the buffer, the result will be equal to
## `buffer.len`. In other words, you can use the function
## like this:
##
## var buffer: array[N, BlockRef]
## let startPos = pool.getBlockRange(headBlock, startSlot, skipStep, buffer)
## for i in startPos ..< buffer.len:
## echo buffer[i].slot
##
result = output.len
trace "getBlockRange entered", headBlock, startSlot, skipStep
var b = pool.getRef(headBlock)
if b == nil:
trace "head block not found", headBlock
return
trace "head block found", headBlock = b
if b.slot < startSlot:
trace "head block is older than startSlot", headBlockSlot = b.slot, startSlot
return
template skip(n: int) =
let targetSlot = b.slot - Slot(n)
while b.slot > targetSlot:
if b.parent == nil:
trace "stopping at parentless block", slot = b.slot, root = b.root
return
trace "skipping block", nextBlock = b.parent
b = b.parent
# We must compute the last block that is eligible for inclusion
# in the results. This will be a block with a slot number that's
# aligned to the stride of the requested block range, so we first
# compute the steps needed to get to an aligned position:
var blocksToSkip = b.slot.int mod skipStep
let alignedHeadSlot = b.slot.int - blocksToSkip
# Then we see if this aligned position is within our wanted
# range. If it's outside it, we must skip more blocks:
let lastWantedSlot = startSlot.int + (output.len - 1) * skipStep
if alignedHeadSlot > lastWantedSlot:
blocksToSkip += (alignedHeadSlot - lastWantedSlot)
# Finally, we skip the computed number of blocks
trace "aligning head", blocksToSkip
skip blocksToSkip
# From here, we can just write out the requested block range:
while b != nil and b.slot >= startSlot and result > 0:
dec result
output[result] = b
trace "getBlockRange result", position = result, blockSlot = b.slot
skip skipStep
proc get*(pool: BlockPool, blck: BlockRef): BlockData =
## Retrieve the associated block body of a block reference
doAssert (not blck.isNil), "Trying to get nil BlockRef"
let data = pool.db.getBlock(blck.root)
doAssert data.isSome, "BlockRef without backing data, database corrupt?"
BlockData(data: data.get(), refs: blck)
proc get*(pool: BlockPool, root: Eth2Digest): Option[BlockData] =
## Retrieve a resolved block reference and its associated body, if available
let refs = pool.getRef(root)
if not refs.isNil:
some(pool.get(refs))
else:
none(BlockData)
func getOrResolve*(pool: var BlockPool, root: Eth2Digest): BlockRef =
## Fetch a block ref, or nil if not found (will be added to list of
## blocks-to-resolve)
result = pool.getRef(root)
if result.isNil:
pool.missing[root] = MissingBlock(slots: 1)
iterator blockRootsForSlot*(pool: BlockPool, slot: Slot): Eth2Digest =
for br in pool.blocksBySlot.getOrDefault(slot, @[]):
yield br.root
func checkMissing*(pool: var BlockPool): seq[FetchRecord] =
## Return a list of blocks that we should try to resolve from other client -
## to be called periodically but not too often (once per slot?)
var done: seq[Eth2Digest]
for k, v in pool.missing.mpairs():
if v.tries > 8:
done.add(k)
else:
inc v.tries
for k in done:
# TODO Need to potentially remove from pool.pending - this is currently a
# memory leak here!
pool.missing.del(k)
# simple (simplistic?) exponential backoff for retries..
for k, v in pool.missing.pairs():
if v.tries.popcount() == 1:
result.add(FetchRecord(root: k, historySlots: v.slots))
proc skipAndUpdateState(
state: var HashedBeaconState, blck: BeaconBlock, flags: UpdateFlags,
afterUpdate: proc (state: HashedBeaconState)): bool =
process_slots(state, blck.slot - 1)
afterUpdate(state)
let ok = state_transition(state, blck, flags)
afterUpdate(state)
ok
proc maybePutState(pool: BlockPool, state: HashedBeaconState, blck: BlockRef) =
# TODO we save state at every epoch start but never remove them - we also
# potentially save multiple states per slot if reorgs happen, meaning
# we could easily see a state explosion
# TODO this is out of sync with epoch def now, I think -- (slot + 1) mod foo.
logScope: pcs = "save_state_at_epoch_start"
if state.data.slot mod SLOTS_PER_EPOCH == 0:
if not pool.db.containsState(state.root):
info "Storing state",
stateSlot = shortLog(state.data.slot),
stateRoot = shortLog(state.root),
cat = "caching"
pool.db.putState(state.root, state.data)
# TODO this should be atomic with the above write..
pool.db.putStateRoot(blck.root, state.data.slot, state.root)
proc rewindState(pool: BlockPool, state: var StateData, bs: BlockSlot):
seq[BlockData] =
logScope: pcs = "replay_state"
var ancestors = @[pool.get(bs.blck)]
# Common case: the last block applied is the parent of the block to apply:
if not bs.blck.parent.isNil and state.blck.root == bs.blck.parent.root and
state.data.data.slot < bs.slot:
return ancestors
# It appears that the parent root of the proposed new block is different from
# what we expected. We will have to rewind the state to a point along the
# chain of ancestors of the new block. We will do this by loading each
# successive parent block and checking if we can find the corresponding state
# in the database.
var
stateRoot = pool.db.getStateRoot(bs.blck.root, bs.slot)
curBs = bs
while stateRoot.isNone():
let parBs = curBs.parent()
if parBs.blck.isNil:
break # Bug probably!
if parBs.blck != curBs.blck:
ancestors.add(pool.get(parBs.blck))
if (let tmp = pool.db.getStateRoot(parBs.blck.root, parBs.slot); tmp.isSome()):
if pool.db.containsState(tmp.get):
stateRoot = tmp
break
curBs = parBs
if stateRoot.isNone():
# TODO this should only happen if the database is corrupt - we walked the
# list of parent blocks and couldn't find a corresponding state in the
# database, which should never happen (at least we should have the
# tail state in there!)
error "Couldn't find ancestor state root!",
blockRoot = shortLog(bs.blck.root),
cat = "crash"
doAssert false, "Oh noes, we passed big bang!"
let
ancestor = ancestors.pop()
ancestorState = pool.db.getState(stateRoot.get())
if ancestorState.isNone():
# TODO this should only happen if the database is corrupt - we walked the
# list of parent blocks and couldn't find a corresponding state in the
# database, which should never happen (at least we should have the
# tail state in there!)
error "Couldn't find ancestor state or block parent missing!",
blockRoot = shortLog(bs.blck.root),
cat = "crash"
doAssert false, "Oh noes, we passed big bang!"
trace "Replaying state transitions",
stateSlot = shortLog(state.data.data.slot),
ancestorStateRoot = shortLog(ancestor.data.message.state_root),
ancestorStateSlot = shortLog(ancestorState.get().slot),
slot = shortLog(bs.slot),
blockRoot = shortLog(bs.blck.root),
ancestors = ancestors.len,
cat = "replay_state"
state.data.data = ancestorState.get()
state.data.root = stateRoot.get()
state.blck = ancestor.refs
ancestors
proc updateStateData*(pool: BlockPool, state: var StateData, bs: BlockSlot) =
## Rewind or advance state such that it matches the given block and slot -
## this may include replaying from an earlier snapshot if blck is on a
## different branch or has advanced to a higher slot number than slot
## If slot is higher than blck.slot, replay will fill in with empty/non-block
## slots, else it is ignored
# We need to check the slot because the state might have moved forwards
# without blocks
if state.blck.root == bs.blck.root and state.data.data.slot <= bs.slot:
if state.data.data.slot != bs.slot:
# Might be that we're moving to the same block but later slot
process_slots(state.data, bs.slot)
pool.maybePutState(state.data, bs.blck)
return # State already at the right spot
let ancestors = rewindState(pool, state, bs)
# If we come this far, we found the state root. The last block on the stack
# is the one that produced this particular state, so we can pop it
# TODO it might be possible to use the latest block hashes from the state to
# do this more efficiently.. whatever!
# Time to replay all the blocks between then and now. We skip one because
# it's the one that we found the state with, and it has already been
# applied
for i in countdown(ancestors.len - 1, 0):
let ok =
skipAndUpdateState(state.data, ancestors[i].data.message, {skipValidation}) do(
state: HashedBeaconState):
pool.maybePutState(state, ancestors[i].refs)
doAssert ok, "Blocks in database should never fail to apply.."
# TODO check if this triggers rest of state transition, or should
process_slots(state.data, bs.slot)
pool.maybePutState(state.data, bs.blck)
state.blck = bs.blck
proc loadTailState*(pool: BlockPool): StateData =
## Load the state associated with the current tail in the pool
let stateRoot = pool.db.getBlock(pool.tail.root).get().message.state_root
StateData(
data: HashedBeaconState(
data: pool.db.getState(stateRoot).get(),
root: stateRoot),
blck: pool.tail
)
proc delBlockAndState(pool: BlockPool, blockRoot: Eth2Digest) =
if (let blk = pool.db.getBlock(blockRoot); blk.isSome):
pool.db.delState(blk.get.message.stateRoot)
pool.db.delBlock(blockRoot)
proc delFinalizedStateIfNeeded(pool: BlockPool, b: BlockRef) =
# Delete finalized state for block `b` from the database, that doesn't need
# to be kept for replaying.
# TODO: Currently the protocol doesn't provide a way to request states,
# so we don't need any of the finalized states, and thus remove all of them
# (except the most recent)
if (let blk = pool.db.getBlock(b.root); blk.isSome):
pool.db.delState(blk.get.message.stateRoot)
proc setTailBlock(pool: BlockPool, newTail: BlockRef) =
## Advance tail block, pruning all the states and blocks with older slots
let oldTail = pool.tail
let fromSlot = oldTail.slot.uint64
let toSlot = newTail.slot.uint64 - 1
assert(toSlot > fromSlot)
for s in fromSlot .. toSlot:
for b in pool.blocksBySlot.getOrDefault(s.Slot, @[]):
pool.delBlockAndState(b.root)
b.children = @[]
b.parent = nil
pool.blocks.del(b.root)
pool.pending.del(b.root)
pool.missing.del(b.root)
pool.blocksBySlot.del(s.Slot)
pool.db.putTailBlock(newTail.root)
pool.tail = newTail
pool.addSlotMapping(newTail)
info "Tail block updated",
slot = newTail.slot,
root = shortLog(newTail.root)
proc updateHead*(pool: BlockPool, newHead: BlockRef) =
## Update what we consider to be the current head, as given by the fork
## choice.
## The choice of head affects the choice of finalization point - the order
## of operations naturally becomes important here - after updating the head,
## blocks that were once considered potential candidates for a tree will
## now fall from grace, or no longer be considered resolved.
doAssert newHead.parent != nil or newHead.slot == 0
logScope: pcs = "fork_choice"
if pool.head.blck == newHead:
info "No head block update",
headBlockRoot = shortLog(newHead.root),
headBlockSlot = shortLog(newHead.slot),
cat = "fork_choice"
return
let
lastHead = pool.head
pool.db.putHeadBlock(newHead.root)
# Start off by making sure we have the right state
updateStateData(
pool, pool.headState, BlockSlot(blck: newHead, slot: newHead.slot))
let
justifiedSlot = pool.headState.data.data
.current_justified_checkpoint
.epoch
.compute_start_slot_at_epoch()
justifiedBS = newHead.findAncestorBySlot(justifiedSlot)
pool.head = Head(blck: newHead, justified: justifiedBS)
updateStateData(pool, pool.justifiedState, justifiedBS)
# TODO isAncestorOf may be expensive - too expensive?
if not lastHead.blck.isAncestorOf(newHead):
info "Updated head block (new parent)",
lastHeadRoot = shortLog(lastHead.blck.root),
parentRoot = shortLog(newHead.parent.root),
stateRoot = shortLog(pool.headState.data.root),
headBlockRoot = shortLog(pool.headState.blck.root),
stateSlot = shortLog(pool.headState.data.data.slot),
justifiedEpoch = shortLog(pool.headState.data.data.current_justified_checkpoint.epoch),
finalizedEpoch = shortLog(pool.headState.data.data.finalized_checkpoint.epoch),
cat = "fork_choice"
# A reasonable criterion for "reorganizations of the chain"
beacon_reorgs_total.inc()
else:
info "Updated head block",
stateRoot = shortLog(pool.headState.data.root),
headBlockRoot = shortLog(pool.headState.blck.root),
stateSlot = shortLog(pool.headState.data.data.slot),
justifiedEpoch = shortLog(pool.headState.data.data.current_justified_checkpoint.epoch),
finalizedEpoch = shortLog(pool.headState.data.data.finalized_checkpoint.epoch),
cat = "fork_choice"
let
finalizedEpochStartSlot =
pool.headState.data.data.finalized_checkpoint.epoch.
compute_start_slot_at_epoch()
# TODO there might not be a block at the epoch boundary - what then?
finalizedHead = newHead.findAncestorBySlot(finalizedEpochStartSlot)
doAssert (not finalizedHead.blck.isNil),
"Block graph should always lead to a finalized block"
if finalizedHead != pool.finalizedHead:
info "Finalized block",
finalizedBlockRoot = shortLog(finalizedHead.blck.root),
finalizedBlockSlot = shortLog(finalizedHead.slot),
headBlockRoot = shortLog(newHead.root),
headBlockSlot = shortLog(newHead.slot),
cat = "fork_choice"
pool.finalizedHead = finalizedHead
var cur = finalizedHead.blck
while cur != pool.finalizedHead.blck:
# Finalization means that we choose a single chain as the canonical one -
# it also means we're no longer interested in any branches from that chain
# up to the finalization point
# TODO technically, if we remove from children the gc should free the block
# because it should become orphaned, via mark&sweep if nothing else,
# though this needs verification
# TODO what about attestations? we need to drop those too, though they
# *should* be pretty harmless
# TODO remove from database as well.. here, or using some GC-like setup
# that periodically cleans it up?
for child in cur.parent.children:
if child != cur:
pool.blocks.del(child.root)
pool.delBlockAndState(child.root)
pool.delSlotMapping(child)
else:
pool.delFinalizedStateIfNeeded(child)
cur.parent.children = @[cur]
cur = cur.parent
let hlen = pool.heads.len
for i in 0..<hlen:
let n = hlen - i - 1
if pool.heads[n].blck.slot < pool.finalizedHead.blck.slot:
# By definition, the current head should be newer than the finalized
# head, so we'll never delete it here
pool.heads.del(n)
# Calculate new tail block and set it
# New tail should be WEAK_SUBJECTIVITY_PERIOD * 2 older than finalizedHead
const tailSlotInterval = WEAK_SUBJECTVITY_PERIOD * 2
if finalizedEpochStartSlot - GENESIS_SLOT > tailSlotInterval:
let tailSlot = finalizedEpochStartSlot - tailSlotInterval
let newTail = finalizedHead.blck.findAncestorBySlot(tailSlot)
pool.setTailBlock(newTail.blck)
func latestJustifiedBlock*(pool: BlockPool): BlockSlot =
## Return the most recent block that is justified and at least as recent
## as the latest finalized block
doAssert pool.heads.len > 0,
"We should have at least the genesis block in heaads"
doAssert (not pool.head.blck.isNil()),
"Genesis block will be head, if nothing else"
# Prefer stability: use justified block from current head to break ties!
result = pool.head.justified
for head in pool.heads[1 ..< ^0]:
if head.justified.slot > result.slot:
result = head.justified
proc preInit*(
T: type BlockPool, db: BeaconChainDB, state: BeaconState,
signedBlock: SignedBeaconBlock) =
# write a genesis state, the way the BlockPool expects it to be stored in
# database
# TODO probably should just init a blockpool with the freshly written
# state - but there's more refactoring needed to make it nice - doing
# a minimal patch for now..
let
blockRoot = hash_tree_root(signedBlock.message)
notice "New database from snapshot",
blockRoot = shortLog(blockRoot),
stateRoot = shortLog(signedBlock.message.state_root),
fork = state.fork,
validators = state.validators.len(),
cat = "initialization"
db.putState(state)
db.putBlock(signedBlock)
db.putTailBlock(blockRoot)
db.putHeadBlock(blockRoot)
db.putStateRoot(
blockRoot, signedBlock.message.slot, signedBlock.message.state_root)
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