Merge pull request #2304 from halseth/weigthed-choice-errnopositive

[autopilot] Don't fail on no more positive nodes

autopilot/agent.go

@@ -366,73 +366,6 @@ func mergeChanState(pendingChans map[NodeID]Channel,
 	return totalChans
 }
 
-// weightedChoice draws a random index from the map of channel candidates, with
-// a probability propotional to their score.
-func weightedChoice(s map[NodeID]*AttachmentDirective) (NodeID, error) {
-	// Calculate the sum of scores found in the map.
-	var sum float64
-	for _, v := range s {
-		sum += v.Score
-	}
-
-	if sum <= 0 {
-		return NodeID{}, fmt.Errorf("non-positive sum")
-	}
-
-	// Create a map of normalized scores such, that they sum to 1.0.
-	norm := make(map[NodeID]float64)
-	for k, v := range s {
-		norm[k] = v.Score / sum
-	}
-
-	// Pick a random number in the range [0.0, 1.0), and iterate the map
-	// until the number goes below 0. This means that each index is picked
-	// with a probablity equal to their normalized score.
-	//
-	// Example:
-	// Items with scores [1, 5, 2, 2]
-	// Normalized scores [0.1, 0.5, 0.2, 0.2]
-	// Imagine they each occupy a "range" equal to their normalized score
-	// in [0, 1.0]:
-	// [|-0.1-||-----0.5-----||--0.2--||--0.2--|]
-	// The following loop is now equivalent to "hitting" the intervals.
-	r := rand.Float64()
-	for k, v := range norm {
-		r -= v
-		if r <= 0 {
-			return k, nil
-		}
-	}
-	return NodeID{}, fmt.Errorf("no choice made")
-}
-
-// chooseN picks at random min[n, len(s)] nodes if from the
-// AttachmentDirectives map, with a probability weighted by their score.
-func chooseN(n int, s map[NodeID]*AttachmentDirective) (
-	map[NodeID]*AttachmentDirective, error) {
-
-	// Keep a map of nodes not yet choosen.
-	rem := make(map[NodeID]*AttachmentDirective)
-	for k, v := range s {
-		rem[k] = v
-	}
-
-	// Pick a weighted choice from the remaining nodes as long as there are
-	// nodes left, and we haven't already picked n.
-	chosen := make(map[NodeID]*AttachmentDirective)
-	for len(chosen) < n && len(rem) > 0 {
-		choice, err := weightedChoice(rem)
-		if err != nil {
-			return nil, err
-		}
-
-		chosen[choice] = rem[choice]
-		delete(rem, choice)
-	}
-
-	return chosen, nil
-}
-
 // controller implements the closed-loop control system of the Agent. The
 // controller will make a decision w.r.t channel placement within the graph
 // based on: its current internal state of the set of active channels open,

autopilot/choice.go

@@ -0,0 +1,80 @@
+package autopilot
+
+import (
+	"errors"
+	"fmt"
+	"math/rand"
+)
+
+// ErrNoPositive is returned from weightedChoice when there are no positive
+// weights left to choose from.
+var ErrNoPositive = errors.New("no positive weights left")
+
+// weightedChoice draws a random index from the map of channel candidates, with
+// a probability propotional to their score.
+func weightedChoice(s map[NodeID]*AttachmentDirective) (NodeID, error) {
+	// Calculate the sum of scores found in the map.
+	var sum float64
+	for _, v := range s {
+		sum += v.Score
+	}
+
+	if sum <= 0 {
+		return NodeID{}, ErrNoPositive
+	}
+
+	// Create a map of normalized scores such, that they sum to 1.0.
+	norm := make(map[NodeID]float64)
+	for k, v := range s {
+		norm[k] = v.Score / sum
+	}
+
+	// Pick a random number in the range [0.0, 1.0), and iterate the map
+	// until the number goes below 0. This means that each index is picked
+	// with a probablity equal to their normalized score.
+	//
+	// Example:
+	// Items with scores [1, 5, 2, 2]
+	// Normalized scores [0.1, 0.5, 0.2, 0.2]
+	// Imagine they each occupy a "range" equal to their normalized score
+	// in [0, 1.0]:
+	// [|-0.1-||-----0.5-----||--0.2--||--0.2--|]
+	// The following loop is now equivalent to "hitting" the intervals.
+	r := rand.Float64()
+	for k, v := range norm {
+		r -= v
+		if r <= 0 {
+			return k, nil
+		}
+	}
+	return NodeID{}, fmt.Errorf("unable to make choice")
+}
+
+// chooseN picks at random min[n, len(s)] nodes if from the
+// AttachmentDirectives map, with a probability weighted by their score.
+func chooseN(n int, s map[NodeID]*AttachmentDirective) (
+	map[NodeID]*AttachmentDirective, error) {
+
+	// Keep a map of nodes not yet choosen.
+	rem := make(map[NodeID]*AttachmentDirective)
+	for k, v := range s {
+		rem[k] = v
+	}
+
+	// Pick a weighted choice from the remaining nodes as long as there are
+	// nodes left, and we haven't already picked n.
+	chosen := make(map[NodeID]*AttachmentDirective)
+	for len(chosen) < n && len(rem) > 0 {
+		choice, err := weightedChoice(rem)
+		if err == ErrNoPositive {
+			return chosen, nil
+		} else if err != nil {
+			return nil, err
+		}
+
+		chosen[choice] = rem[choice]
+		delete(rem, choice)
+	}
+
+	return chosen, nil
+}