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staker_diff_iterator.go
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staker_diff_iterator.go
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// Copyright (C) 2019-2023, Ava Labs, Inc. All rights reserved.
// See the file LICENSE for licensing terms.
package state
import (
"container/heap"
"github.com/ava-labs/avalanchego/vms/platformvm/txs"
)
var (
_ StakerDiffIterator = (*stakerDiffIterator)(nil)
_ StakerIterator = (*mutableStakerIterator)(nil)
_ heap.Interface = (*mutableStakerIterator)(nil)
)
// StakerDiffIterator is an iterator that iterates over the events that will be
// performed on the current staker set.
//
// There are two event types affecting current staker set, removal of an
// existing staker and addition of a new staker from the pending set.
//
// The ordering of operations is:
// - Staker operations are performed in order of their [NextTime].
// - If operations have the same [NextTime], stakers are first added to the
// current staker set, then removed.
// - Further ties are broken by *Staker.Less(), returning the lesser staker
// first.
type StakerDiffIterator interface {
Next() bool
// Returns:
// - The staker that is changing
// - True if the staker is being added to the current staker set, false if
// the staker is being removed from the current staker set
Value() (*Staker, bool)
Release()
}
type stakerDiffIterator struct {
currentIteratorExhausted bool
currentIterator *mutableStakerIterator
pendingIteratorExhausted bool
pendingIterator StakerIterator
modifiedStaker *Staker
isAdded bool
}
func NewStakerDiffIterator(currentIterator, pendingIterator StakerIterator) StakerDiffIterator {
mutableCurrentIterator := newMutableStakerIterator(currentIterator)
return &stakerDiffIterator{
currentIteratorExhausted: !mutableCurrentIterator.Next(),
currentIterator: mutableCurrentIterator,
pendingIteratorExhausted: !pendingIterator.Next(),
pendingIterator: pendingIterator,
}
}
func (it *stakerDiffIterator) Next() bool {
switch {
case it.currentIteratorExhausted && it.pendingIteratorExhausted:
return false
case it.currentIteratorExhausted:
it.advancePending()
case it.pendingIteratorExhausted:
it.advanceCurrent()
default:
nextStakerRemoved := it.currentIterator.Value()
nextStakerAdded := it.pendingIterator.Value()
// If the next operations share the same time, we default to adding the
// staker to the current staker set. This means that we default to
// advancing the pending iterator.
if nextStakerRemoved.EndTime.Before(nextStakerAdded.StartTime) {
it.advanceCurrent()
} else {
it.advancePending()
}
}
return true
}
func (it *stakerDiffIterator) Value() (*Staker, bool) {
return it.modifiedStaker, it.isAdded
}
func (it *stakerDiffIterator) Release() {
it.currentIteratorExhausted = true
it.currentIterator.Release()
it.pendingIteratorExhausted = true
it.pendingIterator.Release()
it.modifiedStaker = nil
}
func (it *stakerDiffIterator) advanceCurrent() {
it.modifiedStaker = it.currentIterator.Value()
it.isAdded = false
it.currentIteratorExhausted = !it.currentIterator.Next()
}
func (it *stakerDiffIterator) advancePending() {
it.modifiedStaker = it.pendingIterator.Value()
it.isAdded = true
it.pendingIteratorExhausted = !it.pendingIterator.Next()
toRemove := *it.modifiedStaker
toRemove.NextTime = toRemove.EndTime
toRemove.Priority = txs.PendingToCurrentPriorities[toRemove.Priority]
it.currentIteratorExhausted = false
it.currentIterator.Add(&toRemove)
}
type mutableStakerIterator struct {
iteratorExhausted bool
iterator StakerIterator
heap []*Staker
}
func newMutableStakerIterator(iterator StakerIterator) *mutableStakerIterator {
return &mutableStakerIterator{
iteratorExhausted: !iterator.Next(),
iterator: iterator,
}
}
// Add should not be called until after Next has been called at least once.
func (it *mutableStakerIterator) Add(staker *Staker) {
heap.Push(it, staker)
}
func (it *mutableStakerIterator) Next() bool {
// The only time the heap should be empty - is when the iterator is
// exhausted or uninitialized.
if len(it.heap) > 0 {
heap.Pop(it)
}
// If the iterator is exhausted, the only elements left to iterate over are
// in the heap.
if it.iteratorExhausted {
return len(it.heap) > 0
}
// If the heap doesn't contain the next staker to return, we need to move
// the next element from the iterator into the heap.
nextIteratorStaker := it.iterator.Value()
if len(it.heap) == 0 || nextIteratorStaker.Less(it.heap[0]) {
it.Add(nextIteratorStaker)
it.iteratorExhausted = !it.iterator.Next()
}
return true
}
func (it *mutableStakerIterator) Value() *Staker {
return it.heap[0]
}
func (it *mutableStakerIterator) Release() {
it.iteratorExhausted = true
it.iterator.Release()
it.heap = nil
}
func (it *mutableStakerIterator) Len() int {
return len(it.heap)
}
func (it *mutableStakerIterator) Less(i, j int) bool {
return it.heap[i].Less(it.heap[j])
}
func (it *mutableStakerIterator) Swap(i, j int) {
it.heap[j], it.heap[i] = it.heap[i], it.heap[j]
}
func (it *mutableStakerIterator) Push(value interface{}) {
it.heap = append(it.heap, value.(*Staker))
}
func (it *mutableStakerIterator) Pop() interface{} {
newLength := len(it.heap) - 1
value := it.heap[newLength]
it.heap[newLength] = nil
it.heap = it.heap[:newLength]
return value
}