blockchain/v2: fix "panic: duplicate block enqueued by processor" (#5499)

When a peer is stopped due to some network issue, the Reactor calls scheduler#handleRemovePeer, which removes the peer from the scheduler. BUT the peer stays in the processor, which sometimes could lead to "duplicate block enqueued by processor" panic WHEN the same block is requested by the scheduler again from a different peer. The solution is to return scPeerError, which will be propagated to the processor. The processor will clean up the blocks associated with the peer in purgePeer.

Closes #5513, #5517

blockchain/v2/routine.go

@@ -2,6 +2,7 @@ package v2
 
 import (
 	"fmt"
+	"strings"
 	"sync/atomic"
 
 	"github.com/Workiva/go-datastructures/queue"
@@ -11,6 +12,8 @@ import (
 
 type handleFunc = func(event Event) (Event, error)
 
+const historySize = 25
+
 // Routine is a structure that models a finite state machine as serialized
 // stream of events processed by a handle function. This Routine structure
 // handles the concurrency and messaging guarantees. Events are sent via
@@ -21,6 +24,7 @@ type Routine struct {
 	name    string
 	handle  handleFunc
 	queue   *queue.PriorityQueue
+	history []Event
 	out     chan Event
 	fin     chan error
 	rdy     chan struct{}
@@ -34,6 +38,7 @@ func newRoutine(name string, handleFunc handleFunc, bufferSize int) *Routine {
 		name:    name,
 		handle:  handleFunc,
 		queue:   queue.NewPriorityQueue(bufferSize, true),
+		history: make([]Event, 0, historySize),
 		out:     make(chan Event, bufferSize),
 		rdy:     make(chan struct{}, 1),
 		fin:     make(chan error, 1),
@@ -53,13 +58,24 @@ func (rt *Routine) setMetrics(metrics *Metrics) {
 }
 
 func (rt *Routine) start() {
-	rt.logger.Info(fmt.Sprintf("%s: run\n", rt.name))
+	rt.logger.Info(fmt.Sprintf("%s: run", rt.name))
 	running := atomic.CompareAndSwapUint32(rt.running, uint32(0), uint32(1))
 	if !running {
 		panic(fmt.Sprintf("%s is already running", rt.name))
 	}
 	close(rt.rdy)
 	defer func() {
+		if r := recover(); r != nil {
+			var (
+				b strings.Builder
+				j int
+			)
+			for i := len(rt.history) - 1; i >= 0; i-- {
+				fmt.Fprintf(&b, "%d: %+v\n", j, rt.history[i])
+				j++
+			}
+			panic(fmt.Sprintf("%v\nlast events:\n%v", r, b.String()))
+		}
 		stopped := atomic.CompareAndSwapUint32(rt.running, uint32(1), uint32(0))
 		if !stopped {
 			panic(fmt.Sprintf("%s is failed to stop", rt.name))
@@ -82,7 +98,19 @@ func (rt *Routine) start() {
 			return
 		}
 		rt.metrics.EventsOut.With("routine", rt.name).Add(1)
-		rt.logger.Debug(fmt.Sprintf("%s: produced %T %+v\n", rt.name, oEvent, oEvent))
+		rt.logger.Debug(fmt.Sprintf("%s: produced %T %+v", rt.name, oEvent, oEvent))
+
+		// Skip rTrySchedule and rProcessBlock events as they clutter the history
+		// due to their frequency.
+		switch events[0].(type) {
+		case rTrySchedule:
+		case rProcessBlock:
+		default:
+			rt.history = append(rt.history, events[0].(Event))
+			if len(rt.history) > historySize {
+				rt.history = rt.history[1:]
+			}
+		}
 
 		rt.out <- oEvent
 	}
@@ -97,7 +125,7 @@ func (rt *Routine) send(event Event) bool {
 	err := rt.queue.Put(event)
 	if err != nil {
 		rt.metrics.EventsShed.With("routine", rt.name).Add(1)
-		rt.logger.Info(fmt.Sprintf("%s: send failed, queue was full/stopped \n", rt.name))
+		rt.logger.Error(fmt.Sprintf("%s: send failed, queue was full/stopped", rt.name))
 		return false
 	}
 
@@ -122,7 +150,7 @@ func (rt *Routine) stop() {
 		return
 	}
 
-	rt.logger.Info(fmt.Sprintf("%s: stop\n", rt.name))
+	rt.logger.Info(fmt.Sprintf("%s: stop", rt.name))
 	rt.queue.Dispose() // this should block until all queue items are free?
 }