Official Go implementation of the Ethereum protocol
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go-ethereum/eth/downloader/resultstore.go

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// Copyright 2020 The go-ethereum Authors
// This file is part of the go-ethereum library.
//
// The go-ethereum library is free software: you can redistribute it and/or modify
// it under the terms of the GNU Lesser General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// The go-ethereum library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU Lesser General Public License for more details.
//
// You should have received a copy of the GNU Lesser General Public License
// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
package downloader
import (
"fmt"
"sync"
"sync/atomic"
"github.com/ethereum/go-ethereum/core/types"
)
// resultStore implements a structure for maintaining fetchResults, tracking their
// download-progress and delivering (finished) results.
type resultStore struct {
items []*fetchResult // Downloaded but not yet delivered fetch results
resultOffset uint64 // Offset of the first cached fetch result in the block chain
// Internal index of first non-completed entry, updated atomically when needed.
// If all items are complete, this will equal length(items), so
// *important* : is not safe to use for indexing without checking against length
indexIncomplete int32 // atomic access
// throttleThreshold is the limit up to which we _want_ to fill the
// results. If blocks are large, we want to limit the results to less
// than the number of available slots, and maybe only fill 1024 out of
// 8192 possible places. The queue will, at certain times, recalibrate
// this index.
throttleThreshold uint64
lock sync.RWMutex
}
func newResultStore(size int) *resultStore {
return &resultStore{
resultOffset: 0,
items: make([]*fetchResult, size),
throttleThreshold: uint64(size),
}
}
// SetThrottleThreshold updates the throttling threshold based on the requested
// limit and the total queue capacity. It returns the (possibly capped) threshold
func (r *resultStore) SetThrottleThreshold(threshold uint64) uint64 {
r.lock.Lock()
defer r.lock.Unlock()
limit := uint64(len(r.items))
if threshold >= limit {
threshold = limit
}
r.throttleThreshold = threshold
return r.throttleThreshold
}
// AddFetch adds a header for body/receipt fetching. This is used when the queue
// wants to reserve headers for fetching.
//
// It returns the following:
//
// stale - if true, this item is already passed, and should not be requested again
// throttled - if true, the store is at capacity, this particular header is not prio now
// item - the result to store data into
// err - any error that occurred
func (r *resultStore) AddFetch(header *types.Header, fastSync bool) (stale, throttled bool, item *fetchResult, err error) {
r.lock.Lock()
defer r.lock.Unlock()
var index int
item, index, stale, throttled, err = r.getFetchResult(header.Number.Uint64())
if err != nil || stale || throttled {
return stale, throttled, item, err
}
if item == nil {
item = newFetchResult(header, fastSync)
r.items[index] = item
}
return stale, throttled, item, err
}
// GetDeliverySlot returns the fetchResult for the given header. If the 'stale' flag
// is true, that means the header has already been delivered 'upstream'. This method
// does not bubble up the 'throttle' flag, since it's moot at the point in time when
// the item is downloaded and ready for delivery
func (r *resultStore) GetDeliverySlot(headerNumber uint64) (*fetchResult, bool, error) {
r.lock.RLock()
defer r.lock.RUnlock()
res, _, stale, _, err := r.getFetchResult(headerNumber)
return res, stale, err
}
// getFetchResult returns the fetchResult corresponding to the given item, and
// the index where the result is stored.
func (r *resultStore) getFetchResult(headerNumber uint64) (item *fetchResult, index int, stale, throttle bool, err error) {
index = int(int64(headerNumber) - int64(r.resultOffset))
throttle = index >= int(r.throttleThreshold)
stale = index < 0
if index >= len(r.items) {
err = fmt.Errorf("%w: index allocation went beyond available resultStore space "+
"(index [%d] = header [%d] - resultOffset [%d], len(resultStore) = %d", errInvalidChain,
index, headerNumber, r.resultOffset, len(r.items))
return nil, index, stale, throttle, err
}
if stale {
return nil, index, stale, throttle, nil
}
item = r.items[index]
return item, index, stale, throttle, nil
}
// hasCompletedItems returns true if there are processable items available
// this method is cheaper than countCompleted
func (r *resultStore) HasCompletedItems() bool {
r.lock.RLock()
defer r.lock.RUnlock()
if len(r.items) == 0 {
return false
}
if item := r.items[0]; item != nil && item.AllDone() {
return true
}
return false
}
// countCompleted returns the number of items ready for delivery, stopping at
// the first non-complete item.
//
// The mthod assumes (at least) rlock is held.
func (r *resultStore) countCompleted() int {
// We iterate from the already known complete point, and see
// if any more has completed since last count
index := atomic.LoadInt32(&r.indexIncomplete)
for ; ; index++ {
if index >= int32(len(r.items)) {
break
}
result := r.items[index]
if result == nil || !result.AllDone() {
break
}
}
atomic.StoreInt32(&r.indexIncomplete, index)
return int(index)
}
// GetCompleted returns the next batch of completed fetchResults
func (r *resultStore) GetCompleted(limit int) []*fetchResult {
r.lock.Lock()
defer r.lock.Unlock()
completed := r.countCompleted()
if limit > completed {
limit = completed
}
results := make([]*fetchResult, limit)
copy(results, r.items[:limit])
// Delete the results from the cache and clear the tail.
copy(r.items, r.items[limit:])
for i := len(r.items) - limit; i < len(r.items); i++ {
r.items[i] = nil
}
// Advance the expected block number of the first cache entry
r.resultOffset += uint64(limit)
atomic.AddInt32(&r.indexIncomplete, int32(-limit))
return results
}
// Prepare initialises the offset with the given block number
func (r *resultStore) Prepare(offset uint64) {
r.lock.Lock()
defer r.lock.Unlock()
if r.resultOffset < offset {
r.resultOffset = offset
}
}