Revert "pick host randomly when distance map is empty (#285)" (#287)

This reverts commit 08d5bef.

services/controllerhost/placement.go

@@ -34,7 +34,6 @@ import (
 )
 
 var errNoHosts = errors.New("Unable to find healthy hosts")
-var errNotEnoughHosts = errors.New("Unable to find enough hosts")
 var errNoInputHosts = errors.New("Unable to find healthy input host")
 var errNoOutputHosts = errors.New("Unable to find healthy output host")
 var errNoStoreHosts = errors.New("Unable to find healthy store hosts")
@@ -78,7 +77,7 @@ func toResources(hosts []*common.HostInfo) []string {
 // Helper function to pick hosts based on the predicates
 func (p *DistancePlacement) pickHosts(service string, poolHosts, sourceHosts []*common.HostInfo, count int, minDistance, maxDistance uint16) ([]*common.HostInfo, error) {
 	if p.distMap == nil {
-		return p.pickRandomHosts(poolHosts, count)
+		return poolHosts[:count], nil
 	}
 
 	sourceResources := toResources(sourceHosts)
@@ -205,8 +204,16 @@ func (p *DistancePlacement) PickStoreHosts(count int) ([]*common.HostInfo, error
 				return hosts, nil
 			}
 		}
-
-		return p.pickRandomHosts(storeHosts, count)
+		if cnt := len(storeHosts); cnt >= count {
+			start := rand.Intn(cnt)
+			end := start + count
+			if end > cnt {
+				end = cnt
+			}
+			hosts := append([]*common.HostInfo{}, storeHosts[start:end]...)
+			hosts = append(hosts, storeHosts[:count-len(hosts)]...)
+			return hosts, nil
+		}
 	}
 
 	return nil, errNoStoreHosts
@@ -297,18 +304,3 @@ func (p *DistancePlacement) findEligibleStoreHosts() ([]*common.HostInfo, error)
 
 	return result, nil
 }
-
-func (p *DistancePlacement) pickRandomHosts(source []*common.HostInfo, count int) ([]*common.HostInfo, error) {
-	if len(source) < count {
-		return nil, errNotEnoughHosts
-	}
-
-	pickedHosts := make([]*common.HostInfo, count)
-	for i, j := range rand.Perm(len(source)) {
-		if i >= count {
-			break
-		}
-		pickedHosts[i] = source[j]
-	}
-	return pickedHosts, nil
-}