351 lines
11 KiB
Go
351 lines
11 KiB
Go
// Copyright 2019 The go-ethereum Authors
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// This file is part of the go-ethereum library.
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//
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// The go-ethereum library is free software: you can redistribute it and/or modify
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// it under the terms of the GNU Lesser General Public License as published by
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// the Free Software Foundation, either version 3 of the License, or
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// (at your option) any later version.
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//
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// The go-ethereum library is distributed in the hope that it will be useful,
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// but WITHOUT ANY WARRANTY; without even the implied warranty of
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// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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// GNU Lesser General Public License for more details.
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//
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// You should have received a copy of the GNU Lesser General Public License
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// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
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package snapshot
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import (
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"bytes"
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"fmt"
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"sort"
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"github.com/ethereum/go-ethereum/common"
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)
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// weightedIterator is a iterator with an assigned weight. It is used to prioritise
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// which account or storage slot is the correct one if multiple iterators find the
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// same one (modified in multiple consecutive blocks).
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type weightedIterator struct {
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it Iterator
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priority int
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}
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// weightedIterators is a set of iterators implementing the sort.Interface.
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type weightedIterators []*weightedIterator
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// Len implements sort.Interface, returning the number of active iterators.
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func (its weightedIterators) Len() int { return len(its) }
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// Less implements sort.Interface, returning which of two iterators in the stack
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// is before the other.
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func (its weightedIterators) Less(i, j int) bool {
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// Order the iterators primarily by the account hashes
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hashI := its[i].it.Hash()
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hashJ := its[j].it.Hash()
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switch bytes.Compare(hashI[:], hashJ[:]) {
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case -1:
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return true
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case 1:
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return false
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}
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// Same account/storage-slot in multiple layers, split by priority
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return its[i].priority < its[j].priority
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}
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// Swap implements sort.Interface, swapping two entries in the iterator stack.
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func (its weightedIterators) Swap(i, j int) {
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its[i], its[j] = its[j], its[i]
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}
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// fastIterator is a more optimized multi-layer iterator which maintains a
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// direct mapping of all iterators leading down to the bottom layer.
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type fastIterator struct {
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tree *Tree // Snapshot tree to reinitialize stale sub-iterators with
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root common.Hash // Root hash to reinitialize stale sub-iterators through
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curAccount []byte
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curSlot []byte
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iterators weightedIterators
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initiated bool
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account bool
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fail error
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}
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// newFastIterator creates a new hierarchical account or storage iterator with one
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// element per diff layer. The returned combo iterator can be used to walk over
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// the entire snapshot diff stack simultaneously.
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func newFastIterator(tree *Tree, root common.Hash, account common.Hash, seek common.Hash, accountIterator bool) (*fastIterator, error) {
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snap := tree.Snapshot(root)
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if snap == nil {
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return nil, fmt.Errorf("unknown snapshot: %x", root)
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}
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fi := &fastIterator{
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tree: tree,
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root: root,
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account: accountIterator,
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}
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current := snap.(snapshot)
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for depth := 0; current != nil; depth++ {
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if accountIterator {
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fi.iterators = append(fi.iterators, &weightedIterator{
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it: current.AccountIterator(seek),
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priority: depth,
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})
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} else {
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// If the whole storage is destructed in this layer, don't
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// bother deeper layer anymore. But we should still keep
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// the iterator for this layer, since the iterator can contain
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// some valid slots which belongs to the re-created account.
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it, destructed := current.StorageIterator(account, seek)
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fi.iterators = append(fi.iterators, &weightedIterator{
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it: it,
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priority: depth,
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})
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if destructed {
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break
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}
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}
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current = current.Parent()
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}
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fi.init()
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return fi, nil
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}
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// init walks over all the iterators and resolves any clashes between them, after
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// which it prepares the stack for step-by-step iteration.
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func (fi *fastIterator) init() {
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// Track which account hashes are iterators positioned on
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var positioned = make(map[common.Hash]int)
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// Position all iterators and track how many remain live
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for i := 0; i < len(fi.iterators); i++ {
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// Retrieve the first element and if it clashes with a previous iterator,
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// advance either the current one or the old one. Repeat until nothing is
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// clashing any more.
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it := fi.iterators[i]
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for {
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// If the iterator is exhausted, drop it off the end
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if !it.it.Next() {
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it.it.Release()
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last := len(fi.iterators) - 1
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fi.iterators[i] = fi.iterators[last]
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fi.iterators[last] = nil
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fi.iterators = fi.iterators[:last]
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i--
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break
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}
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// The iterator is still alive, check for collisions with previous ones
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hash := it.it.Hash()
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if other, exist := positioned[hash]; !exist {
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positioned[hash] = i
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break
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} else {
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// Iterators collide, one needs to be progressed, use priority to
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// determine which.
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//
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// This whole else-block can be avoided, if we instead
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// do an initial priority-sort of the iterators. If we do that,
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// then we'll only wind up here if a lower-priority (preferred) iterator
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// has the same value, and then we will always just continue.
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// However, it costs an extra sort, so it's probably not better
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if fi.iterators[other].priority < it.priority {
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// The 'it' should be progressed
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continue
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} else {
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// The 'other' should be progressed, swap them
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it = fi.iterators[other]
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fi.iterators[other], fi.iterators[i] = fi.iterators[i], fi.iterators[other]
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continue
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}
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}
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}
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}
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// Re-sort the entire list
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sort.Sort(fi.iterators)
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fi.initiated = false
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}
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// Next steps the iterator forward one element, returning false if exhausted.
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func (fi *fastIterator) Next() bool {
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if len(fi.iterators) == 0 {
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return false
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}
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if !fi.initiated {
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// Don't forward first time -- we had to 'Next' once in order to
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// do the sorting already
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fi.initiated = true
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if fi.account {
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fi.curAccount = fi.iterators[0].it.(AccountIterator).Account()
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} else {
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fi.curSlot = fi.iterators[0].it.(StorageIterator).Slot()
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}
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if innerErr := fi.iterators[0].it.Error(); innerErr != nil {
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fi.fail = innerErr
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return false
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}
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if fi.curAccount != nil || fi.curSlot != nil {
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return true
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}
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// Implicit else: we've hit a nil-account or nil-slot, and need to
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// fall through to the loop below to land on something non-nil
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}
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// If an account or a slot is deleted in one of the layers, the key will
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// still be there, but the actual value will be nil. However, the iterator
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// should not export nil-values (but instead simply omit the key), so we
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// need to loop here until we either
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// - get a non-nil value,
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// - hit an error,
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// - or exhaust the iterator
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for {
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if !fi.next(0) {
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return false // exhausted
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}
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if fi.account {
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fi.curAccount = fi.iterators[0].it.(AccountIterator).Account()
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} else {
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fi.curSlot = fi.iterators[0].it.(StorageIterator).Slot()
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}
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if innerErr := fi.iterators[0].it.Error(); innerErr != nil {
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fi.fail = innerErr
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return false // error
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}
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if fi.curAccount != nil || fi.curSlot != nil {
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break // non-nil value found
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}
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}
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return true
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}
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// next handles the next operation internally and should be invoked when we know
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// that two elements in the list may have the same value.
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//
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// For example, if the iterated hashes become [2,3,5,5,8,9,10], then we should
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// invoke next(3), which will call Next on elem 3 (the second '5') and will
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// cascade along the list, applying the same operation if needed.
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func (fi *fastIterator) next(idx int) bool {
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// If this particular iterator got exhausted, remove it and return true (the
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// next one is surely not exhausted yet, otherwise it would have been removed
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// already).
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if it := fi.iterators[idx].it; !it.Next() {
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it.Release()
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fi.iterators = append(fi.iterators[:idx], fi.iterators[idx+1:]...)
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return len(fi.iterators) > 0
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}
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// If there's no one left to cascade into, return
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if idx == len(fi.iterators)-1 {
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return true
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}
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// We next-ed the iterator at 'idx', now we may have to re-sort that element
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var (
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cur, next = fi.iterators[idx], fi.iterators[idx+1]
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curHash, nextHash = cur.it.Hash(), next.it.Hash()
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)
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if diff := bytes.Compare(curHash[:], nextHash[:]); diff < 0 {
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// It is still in correct place
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return true
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} else if diff == 0 && cur.priority < next.priority {
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// So still in correct place, but we need to iterate on the next
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fi.next(idx + 1)
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return true
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}
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// At this point, the iterator is in the wrong location, but the remaining
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// list is sorted. Find out where to move the item.
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clash := -1
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index := sort.Search(len(fi.iterators), func(n int) bool {
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// The iterator always advances forward, so anything before the old slot
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// is known to be behind us, so just skip them altogether. This actually
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// is an important clause since the sort order got invalidated.
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if n < idx {
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return false
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}
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if n == len(fi.iterators)-1 {
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// Can always place an elem last
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return true
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}
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nextHash := fi.iterators[n+1].it.Hash()
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if diff := bytes.Compare(curHash[:], nextHash[:]); diff < 0 {
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return true
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} else if diff > 0 {
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return false
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}
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// The elem we're placing it next to has the same value,
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// so whichever winds up on n+1 will need further iteration
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clash = n + 1
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return cur.priority < fi.iterators[n+1].priority
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})
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fi.move(idx, index)
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if clash != -1 {
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fi.next(clash)
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}
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return true
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}
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// move advances an iterator to another position in the list.
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func (fi *fastIterator) move(index, newpos int) {
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elem := fi.iterators[index]
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copy(fi.iterators[index:], fi.iterators[index+1:newpos+1])
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fi.iterators[newpos] = elem
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}
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// Error returns any failure that occurred during iteration, which might have
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// caused a premature iteration exit (e.g. snapshot stack becoming stale).
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func (fi *fastIterator) Error() error {
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return fi.fail
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}
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// Hash returns the current key
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func (fi *fastIterator) Hash() common.Hash {
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return fi.iterators[0].it.Hash()
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}
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// Account returns the current account blob.
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// Note the returned account is not a copy, please don't modify it.
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func (fi *fastIterator) Account() []byte {
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return fi.curAccount
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}
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// Slot returns the current storage slot.
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// Note the returned slot is not a copy, please don't modify it.
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func (fi *fastIterator) Slot() []byte {
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return fi.curSlot
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}
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// Release iterates over all the remaining live layer iterators and releases each
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// of them individually.
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func (fi *fastIterator) Release() {
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for _, it := range fi.iterators {
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it.it.Release()
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}
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fi.iterators = nil
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}
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// Debug is a convenience helper during testing
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func (fi *fastIterator) Debug() {
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for _, it := range fi.iterators {
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fmt.Printf("[p=%v v=%v] ", it.priority, it.it.Hash()[0])
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}
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fmt.Println()
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}
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// newFastAccountIterator creates a new hierarchical account iterator with one
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// element per diff layer. The returned combo iterator can be used to walk over
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// the entire snapshot diff stack simultaneously.
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func newFastAccountIterator(tree *Tree, root common.Hash, seek common.Hash) (AccountIterator, error) {
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return newFastIterator(tree, root, common.Hash{}, seek, true)
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}
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// newFastStorageIterator creates a new hierarchical storage iterator with one
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// element per diff layer. The returned combo iterator can be used to walk over
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// the entire snapshot diff stack simultaneously.
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func newFastStorageIterator(tree *Tree, root common.Hash, account common.Hash, seek common.Hash) (StorageIterator, error) {
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return newFastIterator(tree, root, account, seek, false)
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}
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