scheduler: pull node shuffle into util

scheduler/feasible.go

@@ -2,7 +2,6 @@ package scheduler
 
 import (
 	"fmt"
-	"math/rand"
 	"reflect"
 	"strings"
 
@@ -68,11 +67,7 @@ func (iter *StaticIterator) Reset() {
 // is applied in-place
 func NewRandomIterator(ctx Context, nodes []*structs.Node) *StaticIterator {
 	// shuffle with the Fisher-Yates algorithm
-	n := len(nodes)
-	for i := n - 1; i > 0; i-- {
-		j := rand.Intn(i + 1)
-		nodes[i], nodes[j] = nodes[j], nodes[i]
-	}
+	shuffleNodes(nodes)
 
 	// Create a static iterator
 	return NewStaticIterator(ctx, nodes)

scheduler/util.go

@@ -2,6 +2,7 @@ package scheduler
 
 import (
 	"fmt"
+	"math/rand"
 
 	"github.com/hashicorp/nomad/nomad/structs"
 )
@@ -195,3 +196,12 @@ func taintedNodes(state State, allocs []*structs.Allocation) (map[string]bool, e
 	}
 	return out, nil
 }
+
+// shuffleNodes randomizes the slice order with the Fisher-Yates algorithm
+func shuffleNodes(nodes []*structs.Node) {
+	n := len(nodes)
+	for i := n - 1; i > 0; i-- {
+		j := rand.Intn(i + 1)
+		nodes[i], nodes[j] = nodes[j], nodes[i]
+	}
+}

scheduler/util_test.go

@@ -3,6 +3,7 @@ package scheduler
 import (
 	"fmt"
 	"os"
+	"reflect"
 	"testing"
 
 	"github.com/hashicorp/nomad/nomad/mock"
@@ -210,3 +211,19 @@ func TestTaintedNodes(t *testing.T) {
 		t.Fatalf("Bad: %v", tainted)
 	}
 }
+
+func TestShuffleNodes(t *testing.T) {
+	nodes := []*structs.Node{
+		mock.Node(),
+		mock.Node(),
+		mock.Node(),
+		mock.Node(),
+		mock.Node(),
+	}
+	orig := make([]*structs.Node, len(nodes))
+	copy(orig, nodes)
+	shuffleNodes(nodes)
+	if reflect.DeepEqual(nodes, orig) {
+		t.Fatalf("shoudl not match")
+	}
+}