core: update blockProcFeed in insertChain (ethereum#31065)

This PR moves the updating of the `blockProcFeed` event feed from
`InsertChain` to `insertChain` in order to ensure that the feed
subscribers are notified whenever block processing happens.
Note that this event is not subscribed to anywhere in our codebase at
the moment, earlier it was used by the LES server to avoid slowing down
block processing. Now I want to do the same with the log indexer, the
problem is that back then every block insertion was done by
`InsertChain`, now the regular payload insertion is done by
`InsertBlockWithoutSetHead`. Both of these (and also `SetCanonical` if
needed) calls `insertChain` so I moved the feed update there.

Author: zsfelfoldi

core/blockchain.go

@@ -235,14 +235,15 @@ type BlockChain struct {
 	statedb       *state.CachingDB                 // State database to reuse between imports (contains state cache)
 	txIndexer     *txIndexer                       // Transaction indexer, might be nil if not enabled
 
-	hc            *HeaderChain
-	rmLogsFeed    event.Feed
-	chainFeed     event.Feed
-	chainHeadFeed event.Feed
-	logsFeed      event.Feed
-	blockProcFeed event.Feed
-	scope         event.SubscriptionScope
-	genesisBlock  *types.Block
+	hc               *HeaderChain
+	rmLogsFeed       event.Feed
+	chainFeed        event.Feed
+	chainHeadFeed    event.Feed
+	logsFeed         event.Feed
+	blockProcFeed    event.Feed
+	blockProcCounter int32
+	scope            event.SubscriptionScope
+	genesisBlock     *types.Block
 
 	// This mutex synchronizes chain write operations.
 	// Readers don't need to take it, they can just read the database.
@@ -1574,8 +1575,6 @@ func (bc *BlockChain) InsertChain(chain types.Blocks) (int, error) {
 	if len(chain) == 0 {
 		return 0, nil
 	}
-	bc.blockProcFeed.Send(true)
-	defer bc.blockProcFeed.Send(false)
 
 	// Do a sanity check that the provided chain is actually ordered and linked.
 	for i := 1; i < len(chain); i++ {
@@ -1615,6 +1614,16 @@ func (bc *BlockChain) insertChain(chain types.Blocks, setHead bool, makeWitness
 	if bc.insertStopped() {
 		return nil, 0, nil
 	}
+
+	if atomic.AddInt32(&bc.blockProcCounter, 1) == 1 {
+		bc.blockProcFeed.Send(true)
+	}
+	defer func() {
+		if atomic.AddInt32(&bc.blockProcCounter, -1) == 0 {
+			bc.blockProcFeed.Send(false)
+		}
+	}()
+
 	// Start a parallel signature recovery (signer will fluke on fork transition, minimal perf loss)
 	SenderCacher().RecoverFromBlocks(types.MakeSigner(bc.chainConfig, chain[0].Number(), chain[0].Time()), chain)