From f55725ebfa77a294d3fa5add869ca4f7dfe09c4f Mon Sep 17 00:00:00 2001
From: Jae Kwon <jae@tendermint.com>
Date: Sat, 26 May 2018 22:08:42 -0700
Subject: [PATCH] Potential fix for blockchain pool halting issue

---
 blockchain/pool.go | 62 ++++++++++++++++++++++++++--------------------
 1 file changed, 35 insertions(+), 27 deletions(-)

diff --git a/blockchain/pool.go b/blockchain/pool.go
index 603b4bf2a..8b964e81a 100644
--- a/blockchain/pool.go
+++ b/blockchain/pool.go
@@ -5,6 +5,7 @@ import (
 	"fmt"
 	"math"
 	"sync"
+	"sync/atomic"
 	"time"
 
 	cmn "github.com/tendermint/tmlibs/common"
@@ -66,11 +67,13 @@ type BlockPool struct {
 	// block requests
 	requesters map[int64]*bpRequester
 	height     int64 // the lowest key in requesters.
-	numPending int32 // number of requests pending assignment or block response
 	// peers
 	peers         map[p2p.ID]*bpPeer
 	maxPeerHeight int64
 
+	// atomic
+	numPending int32 // number of requests pending assignment or block response
+
 	requestsCh chan<- BlockRequest
 	errorsCh   chan<- peerError
 }
@@ -151,7 +154,7 @@ func (pool *BlockPool) GetStatus() (height int64, numPending int32, lenRequester
 	pool.mtx.Lock()
 	defer pool.mtx.Unlock()
 
-	return pool.height, pool.numPending, len(pool.requesters)
+	return pool.height, atomic.LoadInt32(&pool.numPending), len(pool.requesters)
 }
 
 // TODO: relax conditions, prevent abuse.
@@ -245,7 +248,7 @@ func (pool *BlockPool) AddBlock(peerID p2p.ID, block *types.Block, blockSize int
 	}
 
 	if requester.setBlock(block, peerID) {
-		pool.numPending--
+		atomic.AddInt32(&pool.numPending, -1)
 		peer := pool.peers[peerID]
 		if peer != nil {
 			peer.decrPending(blockSize)
@@ -291,10 +294,7 @@ func (pool *BlockPool) RemovePeer(peerID p2p.ID) {
 func (pool *BlockPool) removePeer(peerID p2p.ID) {
 	for _, requester := range pool.requesters {
 		if requester.getPeerID() == peerID {
-			if requester.getBlock() != nil {
-				pool.numPending++
-			}
-			go requester.redo() // pick another peer and ...
+			requester.redo()
 		}
 	}
 	delete(pool.peers, peerID)
@@ -332,7 +332,7 @@ func (pool *BlockPool) makeNextRequester() {
 	// request.SetLogger(pool.Logger.With("height", nextHeight))
 
 	pool.requesters[nextHeight] = request
-	pool.numPending++
+	atomic.AddInt32(&pool.numPending, 1)
 
 	err := request.Start()
 	if err != nil {
@@ -360,7 +360,7 @@ func (pool *BlockPool) sendError(err error, peerID p2p.ID) {
 
 // unused by tendermint; left for debugging purposes
 func (pool *BlockPool) debug() string {
-	pool.mtx.Lock() // Lock
+	pool.mtx.Lock()
 	defer pool.mtx.Unlock()
 
 	str := ""
@@ -466,8 +466,8 @@ func newBPRequester(pool *BlockPool, height int64) *bpRequester {
 	bpr := &bpRequester{
 		pool:       pool,
 		height:     height,
-		gotBlockCh: make(chan struct{}),
-		redoCh:     make(chan struct{}),
+		gotBlockCh: make(chan struct{}, 1),
+		redoCh:     make(chan struct{}, 1),
 
 		peerID: "",
 		block:  nil,
@@ -481,7 +481,7 @@ func (bpr *bpRequester) OnStart() error {
 	return nil
 }
 
-// Returns true if the peer matches
+// Returns true if the peer matches and block doesn't already exist.
 func (bpr *bpRequester) setBlock(block *types.Block, peerID p2p.ID) bool {
 	bpr.mtx.Lock()
 	if bpr.block != nil || bpr.peerID != peerID {
@@ -491,7 +491,10 @@ func (bpr *bpRequester) setBlock(block *types.Block, peerID p2p.ID) bool {
 	bpr.block = block
 	bpr.mtx.Unlock()
 
-	bpr.gotBlockCh <- struct{}{}
+	select {
+	case bpr.gotBlockCh <- struct{}{}:
+	default:
+	}
 	return true
 }
 
@@ -507,17 +510,27 @@ func (bpr *bpRequester) getPeerID() p2p.ID {
 	return bpr.peerID
 }
 
+// This is called from the requestRoutine, upon redo().
 func (bpr *bpRequester) reset() {
 	bpr.mtx.Lock()
+	defer bpr.mtx.Unlock()
+
+	if bpr.block != nil {
+		atomic.AddInt32(&bpr.pool.numPending, 1)
+	}
+
 	bpr.peerID = ""
 	bpr.block = nil
-	bpr.mtx.Unlock()
 }
 
 // Tells bpRequester to pick another peer and try again.
-// NOTE: blocking
+// NOTE: Nonblocking, and does nothing if another redo
+// was already requested.
 func (bpr *bpRequester) redo() {
-	bpr.redoCh <- struct{}{}
+	select {
+	case bpr.redoCh <- struct{}{}:
+	default:
+	}
 }
 
 // Responsible for making more requests as necessary
@@ -546,17 +559,8 @@ OUTER_LOOP:
 
 		// Send request and wait.
 		bpr.pool.sendRequest(bpr.height, peer.id)
-		select {
-		case <-bpr.pool.Quit():
-			bpr.Stop()
-			return
-		case <-bpr.Quit():
-			return
-		case <-bpr.redoCh:
-			bpr.reset()
-			continue OUTER_LOOP // When peer is removed
-		case <-bpr.gotBlockCh:
-			// We got the block, now see if it's good.
+	WAIT_LOOP:
+		for {
 			select {
 			case <-bpr.pool.Quit():
 				bpr.Stop()
@@ -566,6 +570,10 @@ OUTER_LOOP:
 			case <-bpr.redoCh:
 				bpr.reset()
 				continue OUTER_LOOP
+			case <-bpr.gotBlockCh:
+				// We got a block!
+				// Continue the for-loop and wait til Quit.
+				continue WAIT_LOOP
 			}
 		}
 	}