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thresholdstate.go
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thresholdstate.go
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// Copyright (c) 2016-2017 The btcsuite developers
// Use of this source code is governed by an ISC
// license that can be found in the LICENSE file.
package blockchain
import (
"fmt"
"github.com/martinboehm/btcd/chaincfg/chainhash"
)
// ThresholdState define the various threshold states used when voting on
// consensus changes.
type ThresholdState byte
// These constants are used to identify specific threshold states.
const (
// ThresholdDefined is the first state for each deployment and is the
// state for the genesis block has by definition for all deployments.
ThresholdDefined ThresholdState = iota
// ThresholdStarted is the state for a deployment once its start time
// has been reached.
ThresholdStarted
// ThresholdLockedIn is the state for a deployment during the retarget
// period which is after the ThresholdStarted state period and the
// number of blocks that have voted for the deployment equal or exceed
// the required number of votes for the deployment.
ThresholdLockedIn
// ThresholdActive is the state for a deployment for all blocks after a
// retarget period in which the deployment was in the ThresholdLockedIn
// state.
ThresholdActive
// ThresholdFailed is the state for a deployment once its expiration
// time has been reached and it did not reach the ThresholdLockedIn
// state.
ThresholdFailed
// numThresholdsStates is the maximum number of threshold states used in
// tests.
numThresholdsStates
)
// thresholdStateStrings is a map of ThresholdState values back to their
// constant names for pretty printing.
var thresholdStateStrings = map[ThresholdState]string{
ThresholdDefined: "ThresholdDefined",
ThresholdStarted: "ThresholdStarted",
ThresholdLockedIn: "ThresholdLockedIn",
ThresholdActive: "ThresholdActive",
ThresholdFailed: "ThresholdFailed",
}
// String returns the ThresholdState as a human-readable name.
func (t ThresholdState) String() string {
if s := thresholdStateStrings[t]; s != "" {
return s
}
return fmt.Sprintf("Unknown ThresholdState (%d)", int(t))
}
// thresholdConditionChecker provides a generic interface that is invoked to
// determine when a consensus rule change threshold should be changed.
type thresholdConditionChecker interface {
// BeginTime returns the unix timestamp for the median block time after
// which voting on a rule change starts (at the next window).
BeginTime() uint64
// EndTime returns the unix timestamp for the median block time after
// which an attempted rule change fails if it has not already been
// locked in or activated.
EndTime() uint64
// RuleChangeActivationThreshold is the number of blocks for which the
// condition must be true in order to lock in a rule change.
RuleChangeActivationThreshold() uint32
// MinerConfirmationWindow is the number of blocks in each threshold
// state retarget window.
MinerConfirmationWindow() uint32
// Condition returns whether or not the rule change activation condition
// has been met. This typically involves checking whether or not the
// bit associated with the condition is set, but can be more complex as
// needed.
Condition(*blockNode) (bool, error)
}
// thresholdStateCache provides a type to cache the threshold states of each
// threshold window for a set of IDs.
type thresholdStateCache struct {
entries map[chainhash.Hash]ThresholdState
}
// Lookup returns the threshold state associated with the given hash along with
// a boolean that indicates whether or not it is valid.
func (c *thresholdStateCache) Lookup(hash *chainhash.Hash) (ThresholdState, bool) {
state, ok := c.entries[*hash]
return state, ok
}
// Update updates the cache to contain the provided hash to threshold state
// mapping.
func (c *thresholdStateCache) Update(hash *chainhash.Hash, state ThresholdState) {
c.entries[*hash] = state
}
// newThresholdCaches returns a new array of caches to be used when calculating
// threshold states.
func newThresholdCaches(numCaches uint32) []thresholdStateCache {
caches := make([]thresholdStateCache, numCaches)
for i := 0; i < len(caches); i++ {
caches[i] = thresholdStateCache{
entries: make(map[chainhash.Hash]ThresholdState),
}
}
return caches
}
// thresholdState returns the current rule change threshold state for the block
// AFTER the given node and deployment ID. The cache is used to ensure the
// threshold states for previous windows are only calculated once.
//
// This function MUST be called with the chain state lock held (for writes).
func (b *BlockChain) thresholdState(prevNode *blockNode, checker thresholdConditionChecker, cache *thresholdStateCache) (ThresholdState, error) {
// The threshold state for the window that contains the genesis block is
// defined by definition.
confirmationWindow := int32(checker.MinerConfirmationWindow())
if prevNode == nil || (prevNode.height+1) < confirmationWindow {
return ThresholdDefined, nil
}
// Get the ancestor that is the last block of the previous confirmation
// window in order to get its threshold state. This can be done because
// the state is the same for all blocks within a given window.
prevNode = prevNode.Ancestor(prevNode.height -
(prevNode.height+1)%confirmationWindow)
// Iterate backwards through each of the previous confirmation windows
// to find the most recently cached threshold state.
var neededStates []*blockNode
for prevNode != nil {
// Nothing more to do if the state of the block is already
// cached.
if _, ok := cache.Lookup(&prevNode.hash); ok {
break
}
// The start and expiration times are based on the median block
// time, so calculate it now.
medianTime := prevNode.CalcPastMedianTime()
// The state is simply defined if the start time hasn't been
// been reached yet.
if uint64(medianTime.Unix()) < checker.BeginTime() {
cache.Update(&prevNode.hash, ThresholdDefined)
break
}
// Add this node to the list of nodes that need the state
// calculated and cached.
neededStates = append(neededStates, prevNode)
// Get the ancestor that is the last block of the previous
// confirmation window.
prevNode = prevNode.RelativeAncestor(confirmationWindow)
}
// Start with the threshold state for the most recent confirmation
// window that has a cached state.
state := ThresholdDefined
if prevNode != nil {
var ok bool
state, ok = cache.Lookup(&prevNode.hash)
if !ok {
return ThresholdFailed, AssertError(fmt.Sprintf(
"thresholdState: cache lookup failed for %v",
prevNode.hash))
}
}
// Since each threshold state depends on the state of the previous
// window, iterate starting from the oldest unknown window.
for neededNum := len(neededStates) - 1; neededNum >= 0; neededNum-- {
prevNode := neededStates[neededNum]
switch state {
case ThresholdDefined:
// The deployment of the rule change fails if it expires
// before it is accepted and locked in.
medianTime := prevNode.CalcPastMedianTime()
medianTimeUnix := uint64(medianTime.Unix())
if medianTimeUnix >= checker.EndTime() {
state = ThresholdFailed
break
}
// The state for the rule moves to the started state
// once its start time has been reached (and it hasn't
// already expired per the above).
if medianTimeUnix >= checker.BeginTime() {
state = ThresholdStarted
}
case ThresholdStarted:
// The deployment of the rule change fails if it expires
// before it is accepted and locked in.
medianTime := prevNode.CalcPastMedianTime()
if uint64(medianTime.Unix()) >= checker.EndTime() {
state = ThresholdFailed
break
}
// At this point, the rule change is still being voted
// on by the miners, so iterate backwards through the
// confirmation window to count all of the votes in it.
var count uint32
countNode := prevNode
for i := int32(0); i < confirmationWindow; i++ {
condition, err := checker.Condition(countNode)
if err != nil {
return ThresholdFailed, err
}
if condition {
count++
}
// Get the previous block node.
countNode = countNode.parent
}
// The state is locked in if the number of blocks in the
// period that voted for the rule change meets the
// activation threshold.
if count >= checker.RuleChangeActivationThreshold() {
state = ThresholdLockedIn
}
case ThresholdLockedIn:
// The new rule becomes active when its previous state
// was locked in.
state = ThresholdActive
// Nothing to do if the previous state is active or failed since
// they are both terminal states.
case ThresholdActive:
case ThresholdFailed:
}
// Update the cache to avoid recalculating the state in the
// future.
cache.Update(&prevNode.hash, state)
}
return state, nil
}
// ThresholdState returns the current rule change threshold state of the given
// deployment ID for the block AFTER the end of the current best chain.
//
// This function is safe for concurrent access.
func (b *BlockChain) ThresholdState(deploymentID uint32) (ThresholdState, error) {
b.chainLock.Lock()
state, err := b.deploymentState(b.bestChain.Tip(), deploymentID)
b.chainLock.Unlock()
return state, err
}
// IsDeploymentActive returns true if the target deploymentID is active, and
// false otherwise.
//
// This function is safe for concurrent access.
func (b *BlockChain) IsDeploymentActive(deploymentID uint32) (bool, error) {
b.chainLock.Lock()
state, err := b.deploymentState(b.bestChain.Tip(), deploymentID)
b.chainLock.Unlock()
if err != nil {
return false, err
}
return state == ThresholdActive, nil
}
// deploymentState returns the current rule change threshold for a given
// deploymentID. The threshold is evaluated from the point of view of the block
// node passed in as the first argument to this method.
//
// It is important to note that, as the variable name indicates, this function
// expects the block node prior to the block for which the deployment state is
// desired. In other words, the returned deployment state is for the block
// AFTER the passed node.
//
// This function MUST be called with the chain state lock held (for writes).
func (b *BlockChain) deploymentState(prevNode *blockNode, deploymentID uint32) (ThresholdState, error) {
if deploymentID > uint32(len(b.chainParams.Deployments)) {
return ThresholdFailed, DeploymentError(deploymentID)
}
deployment := &b.chainParams.Deployments[deploymentID]
checker := deploymentChecker{deployment: deployment, chain: b}
cache := &b.deploymentCaches[deploymentID]
return b.thresholdState(prevNode, checker, cache)
}
// initThresholdCaches initializes the threshold state caches for each warning
// bit and defined deployment and provides warnings if the chain is current per
// the warnUnknownRuleActivations function.
func (b *BlockChain) initThresholdCaches() error {
// Initialize the warning and deployment caches by calculating the
// threshold state for each of them. This will ensure the caches are
// populated and any states that needed to be recalculated due to
// definition changes is done now.
prevNode := b.bestChain.Tip().parent
for bit := uint32(0); bit < vbNumBits; bit++ {
checker := bitConditionChecker{bit: bit, chain: b}
cache := &b.warningCaches[bit]
_, err := b.thresholdState(prevNode, checker, cache)
if err != nil {
return err
}
}
for id := 0; id < len(b.chainParams.Deployments); id++ {
deployment := &b.chainParams.Deployments[id]
cache := &b.deploymentCaches[id]
checker := deploymentChecker{deployment: deployment, chain: b}
_, err := b.thresholdState(prevNode, checker, cache)
if err != nil {
return err
}
}
// No warnings about unknown rules until the chain is current.
if b.isCurrent() {
bestNode := b.bestChain.Tip()
// Warn if any unknown new rules are either about to activate or
// have already been activated.
if err := b.warnUnknownRuleActivations(bestNode); err != nil {
return err
}
}
return nil
}