refactor: separate responsibilties

Before, priority carried two pieces of information.

One: priority as defined by remote peer
Two: whether task is trashed

This assumes the protocol is defined for natural numbers instead of
integers. That may not always be the case. Better to leave that
assumption outside so this package isn't coupled to the whims of the
protocol.

The protocol may be changed to allow any integer value to be used.
Hopefully by that time, new responsibilties weren't added to the
Priority variable.

License: MIT
Signed-off-by: Brian Tiger Chow <brian@perfmode.com>

strategy/taskqueue.go

@@ -23,6 +23,7 @@ func newTaskQueue() *taskQueue {
 type task struct {
 	Entry  wantlist.Entry
 	Target peer.Peer
+	Trash  bool
 }
 
 // Push currently adds a new task to the end of the list
@@ -55,12 +56,11 @@ func (tl *taskQueue) Pop() *task {
 		out = tl.tasks[0]
 		tl.tasks = tl.tasks[1:]
 		delete(tl.taskmap, taskKey(out.Target, out.Entry.Key))
-		// Filter out blocks that have been cancelled
-		if out.Entry.Priority >= 0 { // FIXME separate the "cancel" signal from priority
-			break
+		if out.Trash {
+			continue // discarding tasks that have been removed
 		}
+		break // and return |out|
 	}
-
 	return out
 }
 
@@ -68,7 +68,7 @@ func (tl *taskQueue) Pop() *task {
 func (tl *taskQueue) Remove(k u.Key, p peer.Peer) {
 	t, ok := tl.taskmap[taskKey(p, k)]
 	if ok {
-		t.Entry.Priority = -1
+		t.Trash = true
 	}
 }