core/filtermaps: make ChainView thread safe (#31671)

This PR makes `filtermaps.ChainView` thread safe because it is used
concurrently both by the indexer and multiple matcher threads. Even
though it represents an immutable view of the chain, adding a mutex lock
to the `blockHash` function is necessary because it does so by extending
its list of non-canonical hashes if the underlying blockchain is
changed.

The unsafe concurrency did cause a panic once after running the unit
tests for several hours and it could also happen during live operation.

Author: zsfelfoldi

core/filtermaps/chain_view.go

@@ -17,6 +17,8 @@
 package filtermaps
 
 import (
+	"sync"
+
 	"github.com/ethereum/go-ethereum/common"
 	"github.com/ethereum/go-ethereum/core/types"
 	"github.com/ethereum/go-ethereum/log"
@@ -39,6 +41,7 @@ type blockchain interface {
 // of the underlying blockchain, it should only possess the block headers
 // and receipts up until the expected chain view head.
 type ChainView struct {
+	lock       sync.Mutex
 	chain      blockchain
 	headNumber uint64
 	hashes     []common.Hash // block hashes starting backwards from headNumber until first canonical hash
@@ -147,6 +150,9 @@ func (cv *ChainView) extendNonCanonical() bool {
 
 // blockHash returns the given block hash without doing the head number check.
 func (cv *ChainView) blockHash(number uint64) common.Hash {
+	cv.lock.Lock()
+	defer cv.lock.Unlock()
+
 	if number+uint64(len(cv.hashes)) <= cv.headNumber {
 		hash := cv.chain.GetCanonicalHash(number)
 		if !cv.extendNonCanonical() {