core/state: improve prefetcher

core/state/trie_prefetcher.go

@@ -17,6 +17,7 @@
 package state
 
 import (
+	"errors"
 	"sync"
 
 	"github.com/ethereum/go-ethereum/common"
@@ -27,6 +28,9 @@ import (
 var (
 	// triePrefetchMetricsPrefix is the prefix under which to publish the metrics.
 	triePrefetchMetricsPrefix = "trie/prefetch/"
+
+	// errTerminated is returned if any invocation is applied on a terminated fetcher.
+	errTerminated = errors.New("fetcher is already terminated")
 )
 
 // triePrefetcher is an active prefetcher, which receives accounts or storage
@@ -43,17 +47,15 @@ type triePrefetcher struct {
 	deliveryMissMeter metrics.Meter
 	accountLoadMeter  metrics.Meter
 	accountDupMeter   metrics.Meter
-	accountSkipMeter  metrics.Meter
 	accountWasteMeter metrics.Meter
 	storageLoadMeter  metrics.Meter
 	storageDupMeter   metrics.Meter
-	storageSkipMeter  metrics.Meter
 	storageWasteMeter metrics.Meter
 }
 
 func newTriePrefetcher(db Database, root common.Hash, namespace string) *triePrefetcher {
 	prefix := triePrefetchMetricsPrefix + namespace
-	p := &triePrefetcher{
+	return &triePrefetcher{
 		db:       db,
 		root:     root,
 		fetchers: make(map[string]*subfetcher), // Active prefetchers use the fetchers map
@@ -61,20 +63,20 @@ func newTriePrefetcher(db Database, root common.Hash, namespace string) *triePre
 		deliveryMissMeter: metrics.GetOrRegisterMeter(prefix+"/deliverymiss", nil),
 		accountLoadMeter:  metrics.GetOrRegisterMeter(prefix+"/account/load", nil),
 		accountDupMeter:   metrics.GetOrRegisterMeter(prefix+"/account/dup", nil),
-		accountSkipMeter:  metrics.GetOrRegisterMeter(prefix+"/account/skip", nil),
 		accountWasteMeter: metrics.GetOrRegisterMeter(prefix+"/account/waste", nil),
 		storageLoadMeter:  metrics.GetOrRegisterMeter(prefix+"/storage/load", nil),
 		storageDupMeter:   metrics.GetOrRegisterMeter(prefix+"/storage/dup", nil),
-		storageSkipMeter:  metrics.GetOrRegisterMeter(prefix+"/storage/skip", nil),
 		storageWasteMeter: metrics.GetOrRegisterMeter(prefix+"/storage/waste", nil),
 	}
-	return p
 }
 
 // close iterates over all the subfetchers, waits on any that were left spinning
-// and reports the stats to the metrics subsystem.  close should not be called
+// and reports the stats to the metrics subsystem.
-// more than once on a triePrefetcher instance.
 func (p *triePrefetcher) close() {
+	// Short circuit if the fetcher is already closed.
+	if p.closed {
+		return
+	}
 	for _, fetcher := range p.fetchers {
 		fetcher.close()
 
@@ -82,8 +84,6 @@ func (p *triePrefetcher) close() {
 			if fetcher.root == p.root {
 				p.accountLoadMeter.Mark(int64(len(fetcher.seen)))
 				p.accountDupMeter.Mark(int64(fetcher.dups))
-				p.accountSkipMeter.Mark(int64(len(fetcher.tasks)))
-
 				for _, key := range fetcher.used {
 					delete(fetcher.seen, string(key))
 				}
@@ -91,8 +91,6 @@ func (p *triePrefetcher) close() {
 			} else {
 				p.storageLoadMeter.Mark(int64(len(fetcher.seen)))
 				p.storageDupMeter.Mark(int64(fetcher.dups))
-				p.storageSkipMeter.Mark(int64(len(fetcher.tasks)))
-
 				for _, key := range fetcher.used {
 					delete(fetcher.seen, string(key))
 				}
@@ -101,50 +99,54 @@ func (p *triePrefetcher) close() {
 		}
 	}
 	p.closed = true
+	p.fetchers = nil
 }
 
-// prefetch schedules a batch of trie items to prefetch. After the prefetcher is closed, all the following tasks scheduled will not be executed.
+// prefetch schedules a batch of trie items to prefetch. After the prefetcher is
+// closed, all the following tasks scheduled will not be executed and an error
+// will be returned.
 //
 // prefetch is called from two locations:
+//
 //  1. Finalize of the state-objects storage roots. This happens at the end
 //     of every transaction, meaning that if several transactions touches
 //     upon the same contract, the parameters invoking this method may be
 //     repeated.
 //  2. Finalize of the main account trie. This happens only once per block.
-func (p *triePrefetcher) prefetch(owner common.Hash, root common.Hash, addr common.Address, keys [][]byte) {
+func (p *triePrefetcher) prefetch(owner common.Hash, root common.Hash, addr common.Address, keys [][]byte) error {
+	if p.closed {
+		return errTerminated
+	}
 	id := p.trieID(owner, root)
 	fetcher := p.fetchers[id]
 	if fetcher == nil {
 		fetcher = newSubfetcher(p.db, p.root, owner, root, addr)
 		p.fetchers[id] = fetcher
 	}
-	fetcher.schedule(keys)
+	return fetcher.schedule(keys)
 }
 
-// trie returns the trie matching the root hash, or nil if the prefetcher doesn't
+// trie returns the trie matching the root hash, or nil if either the fetcher
-// have it. trie is not safe to call concurrently
+// is terminated or the trie is not available.
 func (p *triePrefetcher) trie(owner common.Hash, root common.Hash) Trie {
+	if p.closed {
+		return nil
+	}
 	// Bail if no trie was prefetched for this root
 	fetcher := p.fetchers[p.trieID(owner, root)]
-	if fetcher == nil || fetcher.trie == nil {
+	if fetcher == nil {
 		p.deliveryMissMeter.Mark(1)
 		return nil
 	}
-	if p.closed {
+	return fetcher.peek()
-		return fetcher.db.CopyTrie(fetcher.trie)
-	}
-	trieChan := make(chan Trie)
-	fetcher.copy <- trieChan
-	select {
-	case fetcher.wake <- true:
-	default:
-	}
-	return <-trieChan
 }
 
 // used marks a batch of state items used to allow creating statistics as to
-// how useful or wasteful the prefetcher is.
+// how useful or wasteful the fetcher is.
 func (p *triePrefetcher) used(owner common.Hash, root common.Hash, used [][]byte) {
+	if p.closed {
+		return
+	}
 	if fetcher := p.fetchers[p.trieID(owner, root)]; fetcher != nil {
 		fetcher.used = used
 	}
@@ -173,7 +175,8 @@ type subfetcher struct {
 	tasks [][]byte   // Items queued up for retrieval
 	lock  sync.Mutex // Lock protecting the task queue
 
-	wake chan bool      // Wake channel if a new task is scheduled, true if the subfetcher should continue running when there are no pending tasks
+	wake chan struct{}  // Wake channel if a new task is scheduled
+	stop chan struct{}  // Channel to interrupt processing
 	term chan struct{}  // Channel to signal interruption
 	copy chan chan Trie // channel for retrieving copies of the subfetcher's trie
 
@@ -191,9 +194,10 @@ func newSubfetcher(db Database, state common.Hash, owner common.Hash, root commo
 		owner: owner,
 		root:  root,
 		addr:  addr,
-		wake:  make(chan bool, 1),
+		wake:  make(chan struct{}),
-		copy:  make(chan chan Trie, 1),
+		stop:  make(chan struct{}),
 		term:  make(chan struct{}),
+		copy:  make(chan chan Trie),
 		seen:  make(map[string]struct{}),
 	}
 	go sf.loop()
@@ -201,24 +205,41 @@ func newSubfetcher(db Database, state common.Hash, owner common.Hash, root commo
 }
 
 // schedule adds a batch of trie keys to the queue to prefetch.
-func (sf *subfetcher) schedule(keys [][]byte) {
+func (sf *subfetcher) schedule(keys [][]byte) error {
 	// Append the tasks to the current queue
 	sf.lock.Lock()
-
 	sf.tasks = append(sf.tasks, keys...)
 	sf.lock.Unlock()
-	// Notify the prefetcher, it's fine if it's already terminated
+
+	// Notify the background thread to execute scheduled tasks
 	select {
-	case sf.wake <- true:
+	case sf.wake <- struct{}{}:
-	default:
+		return nil
+	case <-sf.term:
+		return errTerminated
+	}
+}
+
+// peek tries to retrieve a deep copy of the fetcher's trie. Nil is returned
+// if the fetcher is already terminated, or the associated trie is failing
+// for opening.
+func (sf *subfetcher) peek() Trie {
+	ch := make(chan Trie)
+	select {
+	case sf.copy <- ch:
+		return <-ch
+	case <-sf.term:
+		return nil
 	}
 }
 
 // close waits for the subfetcher to finish its tasks. It cannot be called multiple times
 func (sf *subfetcher) close() {
-	// Notify the prefetcher. The wake-chan is buffered, so this is async.
+	select {
-	sf.wake <- false
+	case <-sf.stop:
-	// Wait for it to terminate
+	default:
+		close(sf.stop)
+	}
 	<-sf.term
 }
 
@@ -228,8 +249,7 @@ func (sf *subfetcher) loop() {
 	// No matter how the loop stops, signal anyone waiting that it's terminated
 	defer close(sf.term)
 
-	// Any calls to trie
+	// Start by opening the trie and stop processing if it fails.
-	// start by opening the trie and stop processing if it fails.
 	if sf.owner == (common.Hash{}) {
 		trie, err := sf.db.OpenTrie(sf.root)
 		if err != nil {
@@ -238,8 +258,6 @@ func (sf *subfetcher) loop() {
 		}
 		sf.trie = trie
 	} else {
-		// The trie argument can be nil as verkle doesn't support prefetching
-		// yet. TODO FIX IT(rjl493456442), otherwise code will panic here.
 		trie, err := sf.db.OpenStorageTrie(sf.state, sf.addr, sf.root, nil)
 		if err != nil {
 			log.Warn("Trie prefetcher failed opening trie", "root", sf.root, "err", err)
@@ -248,14 +266,15 @@ func (sf *subfetcher) loop() {
 		sf.trie = trie
 	}
 	// Trie opened successfully, keep prefetching items
-	for keepRunning := range sf.wake {
+	for {
-		// Subfetcher was woken up, retrieve any tasks to avoid spinning the lock
+		select {
+		case <-sf.wake:
+			// Execute all remaining tasks in single run
 			sf.lock.Lock()
 			tasks := sf.tasks
 			sf.tasks = nil
 			sf.lock.Unlock()
 
-		// Prefetch all tasks
 			for _, task := range tasks {
 				if _, ok := sf.seen[string(task)]; ok {
 					sf.dups++
@@ -268,14 +287,12 @@ func (sf *subfetcher) loop() {
 				}
 				sf.seen[string(task)] = struct{}{}
 			}
-		// if any trie retrieval request is made, ensure it is completed
-		// after pending tasks have been processed.
-		select {
 		case ch := <-sf.copy:
+			// Somebody wants a copy of the current trie, grant them.
 			ch <- sf.db.CopyTrie(sf.trie)
-		default:
+
-		}
+		case <-sf.stop:
-		if !keepRunning {
+			// Termination is requested, abort
 			return
 		}
 	}

core/state/trie_prefetcher_test.go

@@ -55,7 +55,7 @@ func TestUseAfterClose(t *testing.T) {
 	if a == nil {
 		t.Fatal("Prefetching before close should not return nil")
 	}
-	if b == nil {
+	if b != nil {
-		t.Fatal("Trie after close should not return nil")
+		t.Fatal("Trie after close should return nil")
 	}
 }