some code cleanup and commenting

exchange/bitswap/decision/engine.go

@@ -55,9 +55,6 @@ type Envelope struct {
 	Peer peer.ID
 	// Message is the payload
 	Message bsmsg.BitSwapMessage
-
-	// A callback to notify the decision queue that the task is complete
-	Sent func()
 }
 
 type Engine struct {
@@ -143,7 +140,6 @@ func (e *Engine) nextEnvelope(ctx context.Context) (*Envelope, error) {
 		return &Envelope{
 			Peer:    nextTask.Target,
 			Message: m,
-			Sent:    nextTask.Done,
 		}, nil
 	}
 }

exchange/bitswap/decision/peer_request_queue.go

@@ -27,6 +27,7 @@ func newPRQ() peerRequestQueue {
 	}
 }
 
+// verify interface implementation
 var _ peerRequestQueue = &prq{}
 
 // TODO: at some point, the strategy needs to plug in here
@@ -81,12 +82,7 @@ func (tl *prq) Pop() *peerRequestTask {
 	if tl.pQueue.Len() == 0 {
 		return nil
 	}
-	pElem := tl.pQueue.Pop()
-	if pElem == nil {
-		return nil
-	}
-
-	partner := pElem.(*activePartner)
+	partner := tl.pQueue.Pop().(*activePartner)
 
 	var out *peerRequestTask
 	for partner.taskQueue.Len() > 0 {
@@ -97,6 +93,8 @@ func (tl *prq) Pop() *peerRequestTask {
 		}
 		break // and return |out|
 	}
+
+	// start the new task, and push the partner back onto the queue
 	partner.StartTask()
 	partner.requests--
 	tl.pQueue.Push(partner)
@@ -112,6 +110,8 @@ func (tl *prq) Remove(k u.Key, p peer.ID) {
 		// simply mark it as trash, so it'll be dropped when popped off the
 		// queue.
 		t.trash = true
+
+		// having canceled a block, we now account for that in the given partner
 		tl.partners[p].requests--
 	}
 	tl.lock.Unlock()
@@ -121,6 +121,7 @@ type peerRequestTask struct {
 	Entry  wantlist.Entry
 	Target peer.ID
 
+	// A callback to signal that this task has been completed
 	Done func()
 
 	// trash in a book-keeping field
@@ -135,10 +136,12 @@ func (t *peerRequestTask) Key() string {
 	return taskKey(t.Target, t.Entry.Key)
 }
 
+// Index implements pq.Elem
 func (t *peerRequestTask) Index() int {
 	return t.index
 }
 
+// SetIndex implements pq.Elem
 func (t *peerRequestTask) SetIndex(i int) {
 	t.index = i
 }
@@ -172,17 +175,22 @@ type activePartner struct {
 	lk sync.Mutex
 
 	// Active is the number of blocks this peer is currently being sent
+	// active must be locked around as it will be updated externally
 	active int
 
 	// requests is the number of blocks this peer is currently requesting
+	// request need not be locked around as it will only be modified under
+	// the peerRequestQueue's locks
 	requests int
 
+	// for the PQ interface
 	index int
 
-	// priority queue of
+	// priority queue of tasks belonging to this peer
 	taskQueue pq.PQ
 }
 
+// partnerCompare implements pq.ElemComparator
 func partnerCompare(a, b pq.Elem) bool {
 	pa := a.(*activePartner)
 	pb := b.(*activePartner)
@@ -197,12 +205,14 @@ func partnerCompare(a, b pq.Elem) bool {
 	return pa.active < pb.active
 }
 
+// StartTask signals that a task was started for this partner
 func (p *activePartner) StartTask() {
 	p.lk.Lock()
 	p.active++
 	p.lk.Unlock()
 }
 
+// TaskDone signals that a task was completed for this partner
 func (p *activePartner) TaskDone() {
 	p.lk.Lock()
 	p.active--
@@ -212,10 +222,12 @@ func (p *activePartner) TaskDone() {
 	p.lk.Unlock()
 }
 
+// Index implements pq.Elem
 func (p *activePartner) Index() int {
 	return p.index
 }
 
+// SetIndex implements pq.Elem
 func (p *activePartner) SetIndex(i int) {
 	p.index = i
 }