forked from cerc-io/plugeth
core/state/snapshot: fix data race in layer flattening (#23628)
* core/state/snapshot: fix data race in layer flattening * core/state/snapshot: fix typo
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@ -163,6 +163,9 @@ type Tree struct {
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cache int // Megabytes permitted to use for read caches
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layers map[common.Hash]snapshot // Collection of all known layers
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lock sync.RWMutex
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// Test hooks
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onFlatten func() // Hook invoked when the bottom most diff layers are flattened
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}
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// New attempts to load an already existing snapshot from a persistent key-value
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@ -463,14 +466,21 @@ func (t *Tree) cap(diff *diffLayer, layers int) *diskLayer {
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return nil
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case *diffLayer:
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// Hold the write lock until the flattened parent is linked correctly.
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// Otherwise, the stale layer may be accessed by external reads in the
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// meantime.
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diff.lock.Lock()
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defer diff.lock.Unlock()
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// Flatten the parent into the grandparent. The flattening internally obtains a
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// write lock on grandparent.
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flattened := parent.flatten().(*diffLayer)
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t.layers[flattened.root] = flattened
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diff.lock.Lock()
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defer diff.lock.Unlock()
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// Invoke the hook if it's registered. Ugly hack.
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if t.onFlatten != nil {
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t.onFlatten()
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}
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diff.parent = flattened
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if flattened.memory < aggregatorMemoryLimit {
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// Accumulator layer is smaller than the limit, so we can abort, unless
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@ -22,6 +22,7 @@ import (
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"math/big"
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"math/rand"
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"testing"
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"time"
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"github.com/VictoriaMetrics/fastcache"
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"github.com/ethereum/go-ethereum/common"
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@ -324,7 +325,7 @@ func TestPostCapBasicDataAccess(t *testing.T) {
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}
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}
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// TestSnaphots tests the functionality for retrieveing the snapshot
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// TestSnaphots tests the functionality for retrieving the snapshot
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// with given head root and the desired depth.
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func TestSnaphots(t *testing.T) {
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// setAccount is a helper to construct a random account entry and assign it to
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@ -423,3 +424,63 @@ func TestSnaphots(t *testing.T) {
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}
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}
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}
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// TestReadStateDuringFlattening tests the scenario that, during the
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// bottom diff layers are merging which tags these as stale, the read
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// happens via a pre-created top snapshot layer which tries to access
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// the state in these stale layers. Ensure this read can retrieve the
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// right state back(block until the flattening is finished) instead of
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// an unexpected error(snapshot layer is stale).
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func TestReadStateDuringFlattening(t *testing.T) {
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// setAccount is a helper to construct a random account entry and assign it to
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// an account slot in a snapshot
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setAccount := func(accKey string) map[common.Hash][]byte {
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return map[common.Hash][]byte{
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common.HexToHash(accKey): randomAccount(),
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}
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}
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// Create a starting base layer and a snapshot tree out of it
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base := &diskLayer{
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diskdb: rawdb.NewMemoryDatabase(),
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root: common.HexToHash("0x01"),
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cache: fastcache.New(1024 * 500),
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}
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snaps := &Tree{
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layers: map[common.Hash]snapshot{
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base.root: base,
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},
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}
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// 4 layers in total, 3 diff layers and 1 disk layers
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snaps.Update(common.HexToHash("0xa1"), common.HexToHash("0x01"), nil, setAccount("0xa1"), nil)
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snaps.Update(common.HexToHash("0xa2"), common.HexToHash("0xa1"), nil, setAccount("0xa2"), nil)
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snaps.Update(common.HexToHash("0xa3"), common.HexToHash("0xa2"), nil, setAccount("0xa3"), nil)
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// Obtain the topmost snapshot handler for state accessing
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snap := snaps.Snapshot(common.HexToHash("0xa3"))
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// Register the testing hook to access the state after flattening
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var result = make(chan *Account)
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snaps.onFlatten = func() {
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// Spin up a thread to read the account from the pre-created
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// snapshot handler. It's expected to be blocked.
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go func() {
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account, _ := snap.Account(common.HexToHash("0xa1"))
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result <- account
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}()
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select {
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case res := <-result:
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t.Fatalf("Unexpected return %v", res)
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case <-time.NewTimer(time.Millisecond * 300).C:
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}
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}
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// Cap the snap tree, which will mark the bottom-most layer as stale.
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snaps.Cap(common.HexToHash("0xa3"), 1)
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select {
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case account := <-result:
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if account == nil {
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t.Fatal("Failed to retrieve account")
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}
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case <-time.NewTimer(time.Millisecond * 300).C:
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t.Fatal("Unexpected blocker")
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}
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}
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