196 lines
6.3 KiB
Go
196 lines
6.3 KiB
Go
// Copyright 2020 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 downloader
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import (
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"fmt"
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"sync"
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"sync/atomic"
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"github.com/ethereum/go-ethereum/core/types"
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)
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// resultStore implements a structure for maintaining fetchResults, tracking their
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// download-progress and delivering (finished) results.
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type resultStore struct {
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items []*fetchResult // Downloaded but not yet delivered fetch results
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resultOffset uint64 // Offset of the first cached fetch result in the block chain
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// Internal index of first non-completed entry, updated atomically when needed.
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// If all items are complete, this will equal length(items), so
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// *important* : is not safe to use for indexing without checking against length
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indexIncomplete atomic.Int32
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// throttleThreshold is the limit up to which we _want_ to fill the
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// results. If blocks are large, we want to limit the results to less
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// than the number of available slots, and maybe only fill 1024 out of
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// 8192 possible places. The queue will, at certain times, recalibrate
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// this index.
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throttleThreshold uint64
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lock sync.RWMutex
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}
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func newResultStore(size int) *resultStore {
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return &resultStore{
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resultOffset: 0,
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items: make([]*fetchResult, size),
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throttleThreshold: uint64(size),
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}
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}
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// SetThrottleThreshold updates the throttling threshold based on the requested
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// limit and the total queue capacity. It returns the (possibly capped) threshold
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func (r *resultStore) SetThrottleThreshold(threshold uint64) uint64 {
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r.lock.Lock()
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defer r.lock.Unlock()
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limit := uint64(len(r.items))
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if threshold >= limit {
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threshold = limit
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}
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r.throttleThreshold = threshold
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return r.throttleThreshold
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}
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// AddFetch adds a header for body/receipt fetching. This is used when the queue
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// wants to reserve headers for fetching.
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//
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// It returns the following:
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//
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// stale - if true, this item is already passed, and should not be requested again
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// throttled - if true, the store is at capacity, this particular header is not prio now
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// item - the result to store data into
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// err - any error that occurred
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func (r *resultStore) AddFetch(header *types.Header, fastSync bool, pid string) (stale, throttled bool, item *fetchResult, err error) {
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r.lock.Lock()
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defer r.lock.Unlock()
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var index int
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item, index, stale, throttled, err = r.getFetchResult(header.Number.Uint64())
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if err != nil || stale || throttled {
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return stale, throttled, item, err
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}
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if item == nil {
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item = newFetchResult(header, fastSync, pid)
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r.items[index] = item
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}
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return stale, throttled, item, err
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}
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// GetDeliverySlot returns the fetchResult for the given header. If the 'stale' flag
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// is true, that means the header has already been delivered 'upstream'. This method
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// does not bubble up the 'throttle' flag, since it's moot at the point in time when
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// the item is downloaded and ready for delivery
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func (r *resultStore) GetDeliverySlot(headerNumber uint64) (*fetchResult, bool, error) {
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r.lock.RLock()
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defer r.lock.RUnlock()
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res, _, stale, _, err := r.getFetchResult(headerNumber)
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return res, stale, err
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}
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// getFetchResult returns the fetchResult corresponding to the given item, and
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// the index where the result is stored.
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func (r *resultStore) getFetchResult(headerNumber uint64) (item *fetchResult, index int, stale, throttle bool, err error) {
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index = int(int64(headerNumber) - int64(r.resultOffset))
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throttle = index >= int(r.throttleThreshold)
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stale = index < 0
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if index >= len(r.items) {
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err = fmt.Errorf("%w: index allocation went beyond available resultStore space "+
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"(index [%d] = header [%d] - resultOffset [%d], len(resultStore) = %d", errInvalidChain,
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index, headerNumber, r.resultOffset, len(r.items))
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return nil, index, stale, throttle, err
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}
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if stale {
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return nil, index, stale, throttle, nil
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}
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item = r.items[index]
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return item, index, stale, throttle, nil
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}
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// HasCompletedItems returns true if there are processable items available
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// this method is cheaper than countCompleted
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func (r *resultStore) HasCompletedItems() bool {
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r.lock.RLock()
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defer r.lock.RUnlock()
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if len(r.items) == 0 {
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return false
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}
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if item := r.items[0]; item != nil && item.AllDone() {
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return true
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}
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return false
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}
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// countCompleted returns the number of items ready for delivery, stopping at
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// the first non-complete item.
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//
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// The method assumes (at least) rlock is held.
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func (r *resultStore) countCompleted() int {
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// We iterate from the already known complete point, and see
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// if any more has completed since last count
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index := r.indexIncomplete.Load()
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for ; ; index++ {
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if index >= int32(len(r.items)) {
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break
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}
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result := r.items[index]
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if result == nil || !result.AllDone() {
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break
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}
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}
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r.indexIncomplete.Store(index)
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return int(index)
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}
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// GetCompleted returns the next batch of completed fetchResults
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func (r *resultStore) GetCompleted(limit int) []*fetchResult {
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r.lock.Lock()
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defer r.lock.Unlock()
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completed := r.countCompleted()
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if limit > completed {
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limit = completed
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}
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results := make([]*fetchResult, limit)
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copy(results, r.items[:limit])
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// Delete the results from the cache and clear the tail.
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copy(r.items, r.items[limit:])
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for i := len(r.items) - limit; i < len(r.items); i++ {
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r.items[i] = nil
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}
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// Advance the expected block number of the first cache entry
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r.resultOffset += uint64(limit)
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r.indexIncomplete.Add(int32(-limit))
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return results
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}
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// Prepare initialises the offset with the given block number
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func (r *resultStore) Prepare(offset uint64) {
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r.lock.Lock()
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defer r.lock.Unlock()
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if r.resultOffset < offset {
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r.resultOffset = offset
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}
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}
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