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latest_block_changed_event.go
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latest_block_changed_event.go
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package rpcfilters
import (
"errors"
"sync"
"time"
"github.com/ethereum/go-ethereum/common"
"github.com/ethereum/go-ethereum/log"
)
const (
defaultTickerPeriod = 3 * time.Second
defaultReportHistorySize = 20
)
// ringArray represents a thread-safe capped collection of hashes.
type ringArray struct {
mu sync.Mutex
maxCount int
currentIndex int
blocks []common.Hash
}
func newRingArray(maxCount int) *ringArray {
return &ringArray{
maxCount: maxCount,
blocks: make([]common.Hash, maxCount),
}
}
// TryAddUnique adds a hash to the array if the array doesn't have it.
// Returns true if the element was added.
func (r *ringArray) TryAddUnique(hash common.Hash) bool {
r.mu.Lock()
defer r.mu.Unlock()
if r.has(hash) {
return false
}
r.blocks[r.currentIndex] = hash
r.currentIndex++
if r.currentIndex >= len(r.blocks) {
r.currentIndex = 0
}
return true
}
// has returns `true` if the hash is in the array.
// It has linear complexity but on short arrays it isn't worth optimizing.
func (r *ringArray) has(hash common.Hash) bool {
for _, h := range r.blocks {
if h == hash {
return true
}
}
return false
}
// latestBlockChangedEvent represents an event that one can subscribe to
type latestBlockChangedEvent struct {
sxMu sync.Mutex
sx map[int]chan common.Hash
reportedBlocks *ringArray
provider latestBlockProvider
quit chan struct{}
tickerPeriod time.Duration
}
func (e *latestBlockChangedEvent) Start() error {
if e.quit != nil {
return errors.New("latest block changed event is already started")
}
e.quit = make(chan struct{})
go func() {
ticker := time.NewTicker(e.tickerPeriod)
for {
select {
case <-ticker.C:
if e.numberOfSubscriptions() == 0 {
continue
}
latestBlock, err := e.provider.GetLatestBlock()
if err != nil {
log.Error("error while receiving latest block", "error", err)
continue
}
e.processLatestBlock(latestBlock)
case <-e.quit:
return
}
}
}()
return nil
}
func (e *latestBlockChangedEvent) numberOfSubscriptions() int {
e.sxMu.Lock()
defer e.sxMu.Unlock()
return len(e.sx)
}
func (e *latestBlockChangedEvent) processLatestBlock(latestBlock blockInfo) {
// if we received the hash we already received before, don't add it
if !e.reportedBlocks.TryAddUnique(latestBlock.Hash) {
return
}
e.sxMu.Lock()
defer e.sxMu.Unlock()
for _, channel := range e.sx {
channel <- latestBlock.Hash
}
}
func (e *latestBlockChangedEvent) Stop() {
if e.quit == nil {
return
}
select {
case <-e.quit:
e.quit = nil
return
default:
close(e.quit)
}
e.quit = nil
}
func (e *latestBlockChangedEvent) Subscribe() (int, chan common.Hash) {
e.sxMu.Lock()
defer e.sxMu.Unlock()
channel := make(chan common.Hash)
id := len(e.sx)
e.sx[id] = channel
return id, channel
}
func (e *latestBlockChangedEvent) Unsubscribe(id int) {
e.sxMu.Lock()
defer e.sxMu.Unlock()
delete(e.sx, id)
}
func newLatestBlockChangedEvent(provider latestBlockProvider) *latestBlockChangedEvent {
return &latestBlockChangedEvent{
sx: make(map[int]chan common.Hash),
provider: provider,
reportedBlocks: newRingArray(defaultReportHistorySize),
tickerPeriod: defaultTickerPeriod,
}
}