From c142a59eb68ce813bbde9f8500262988ae707eaa Mon Sep 17 00:00:00 2001
From: HonzaDajc <jan.dajc@gmail.com>
Date: Tue, 31 Oct 2023 11:24:42 +0100
Subject: [PATCH] Remove parallel procesing for debug_traceBlock

Because of preparing data for replaying transaction with EVM which is
slower with javascript tracer execution, deep copy of stateDB is created
and every transaction is replayed twice. So this is contra productive.
---
 ethapi/api.go | 71 ++++++++++-----------------------------------------
 1 file changed, 14 insertions(+), 57 deletions(-)

diff --git a/ethapi/api.go b/ethapi/api.go
index 3149c6700..4165a47ac 100644
--- a/ethapi/api.go
+++ b/ethapi/api.go
@@ -22,9 +22,7 @@ import (
 	"fmt"
 	"math/big"
 	"math/rand"
-	"runtime"
 	"strings"
-	"sync"
 	"time"
 
 	"github.com/Fantom-foundation/lachesis-base/hash"
@@ -2180,6 +2178,9 @@ func (api *PublicDebugAPI) traceTx(ctx context.Context, message evmcore.Message,
 		return nil, fmt.Errorf("tracing failed: %w", err)
 	}
 
+	// Finalize the state so any modifications are written to the trie
+	statedb.Finalise(vmenv.ChainConfig().IsByzantium(vmctx.BlockNumber) || vmenv.ChainConfig().IsEIP158(vmctx.BlockNumber))
+
 	// Depending on the tracer type, format and return the output.
 	switch tracer := tracer.(type) {
 	case *vm.StructLogger:
@@ -2222,13 +2223,6 @@ type txTraceResult struct {
 	Error  string      `json:"error,omitempty"`  // Trace failure produced by the tracer
 }
 
-// txTraceTask represents a single transaction trace task when an entire block
-// is being traced.
-type txTraceTask struct {
-	statedb *state.StateDB // Intermediate state prepped for tracing
-	index   int            // Transaction offset in the block
-}
-
 // TraceBlockByNumber returns the structured logs created during the execution of
 // EVM and returns them as a JSON object.
 func (api *PublicDebugAPI) TraceBlockByNumber(ctx context.Context, number rpc.BlockNumber, config *TraceConfig) ([]*txTraceResult, error) {
@@ -2291,64 +2285,27 @@ func (api *PublicDebugAPI) traceBlock(ctx context.Context, block *evmcore.EvmBlo
 		signer  = types.MakeSigner(api.b.ChainConfig(), block.Number)
 		txs     = block.Transactions
 		results = make([]*txTraceResult, len(txs))
-
-		pend = new(sync.WaitGroup)
-		jobs = make(chan *txTraceTask, len(txs))
 	)
-	threads := runtime.NumCPU()
-	if threads > len(txs) {
-		threads = len(txs)
-	}
 
 	blockHeader := block.Header()
 	blockHash := block.Hash
-	for th := 0; th < threads; th++ {
-		pend.Add(1)
-		go func() {
-			defer pend.Done()
-			blockCtx := api.b.GetBlockContext(blockHeader)
-
-			// Fetch and execute the next transaction trace tasks
-			for task := range jobs {
-				msg, _ := txs[task.index].AsMessage(signer, block.BaseFee)
-				txctx := &tracers.Context{
-					BlockHash: blockHash,
-					TxIndex:   task.index,
-					TxHash:    txs[task.index].Hash(),
-				}
-				res, err := api.traceTx(ctx, msg, txctx, blockCtx, task.statedb, config)
-				if err != nil {
-					results[task.index] = &txTraceResult{Error: err.Error()}
-					continue
-				}
-				results[task.index] = &txTraceResult{Result: res}
-			}
-		}()
-	}
+
 	// Feed the transactions into the tracers and return
 	blockCtx := api.b.GetBlockContext(blockHeader)
-	var failed error
 	for i, tx := range txs {
-		// Send the trace task over for execution
-		jobs <- &txTraceTask{statedb: statedb.Copy(), index: i}
 
-		// Generate the next state snapshot fast without tracing
+		txctx := &tracers.Context{
+			BlockHash: blockHash,
+			TxIndex:   i,
+			TxHash:    txs[i].Hash(),
+		}
 		msg, _ := tx.AsMessage(signer, block.BaseFee)
-		statedb.Prepare(tx.Hash(), i)
-		vmenv := vm.NewEVM(blockCtx, evmcore.NewEVMTxContext(msg), statedb, api.b.ChainConfig(), opera.DefaultVMConfig)
-		if _, err := evmcore.ApplyMessage(vmenv, msg, new(evmcore.GasPool).AddGas(msg.Gas())); err != nil {
-			failed = err
-			break
+		res, err := api.traceTx(ctx, msg, txctx, blockCtx, statedb, config)
+		if err != nil {
+			results[i] = &txTraceResult{Error: err.Error()}
+			continue
 		}
-		// Finalize the state so any modifications are written to the trie
-		statedb.Finalise(vmenv.ChainConfig().IsByzantium(block.Number) || vmenv.ChainConfig().IsEIP158(block.Number))
-	}
-	close(jobs)
-	pend.Wait()
-
-	// If execution failed in between, abort
-	if failed != nil {
-		return nil, failed
+		results[i] = &txTraceResult{Result: res}
 	}
 	return results, nil
 }