mmaprototype: convert block to function returning boolean flags

Convert the shedStore block to an IIFE that returns (bool, bool) for
shouldReturnEarly and shouldContinue. Replace all flag assignments with
return statements. This prepares the code for adding more return values
and parameters.

Author: tbg

pkg/kv/kvserver/allocator/mmaprototype/cluster_state_rebalance_stores.go

@@ -147,9 +147,7 @@ func (cs *clusterState) rebalanceStores(
 	rangeMoveCount := 0
 	leaseTransferCount := 0
 	for idx /*logging only*/, store := range sheddingStores {
-		shouldReturnEarly := false
-		shouldContinue := false
-		{
+		shouldReturnEarly, shouldContinue := func() (bool, bool) {
 			log.KvDistribution.Infof(ctx, "start processing shedding store s%d: cpu node load %s, store load %s, worst dim %s",
 				store.StoreID, store.nls, store.sls, store.worstDim)
 			ss := cs.stores[store.StoreID]
@@ -343,8 +341,7 @@ func (cs *clusterState) rebalanceStores(
 						targetSS.maxFractionPendingIncrease, targetSS.maxFractionPendingDecrease)
 					if leaseTransferCount >= maxLeaseTransferCount {
 						log.KvDistribution.VInfof(ctx, 2, "reached max lease transfer count %d, returning", maxLeaseTransferCount)
-						shouldReturnEarly = true
-						break
+						return true, false
 					}
 					doneShedding = ss.maxFractionPendingDecrease >= maxFractionPendingThreshold
 					if doneShedding {
@@ -363,8 +360,7 @@ func (cs *clusterState) rebalanceStores(
 					// lease transfers -- so be it.
 					log.KvDistribution.VInfof(ctx, 2, "skipping replica transfers for s%d: done shedding=%v, lease_transfers=%d",
 						store.StoreID, doneShedding, leaseTransferCount)
-					shouldContinue = true
-					break
+					return false, true
 				}
 			} else {
 				log.KvDistribution.VInfof(ctx, 2, "skipping lease shedding: s%v != local store s%s or cpu is not overloaded: %v",
@@ -376,8 +372,7 @@ func (cs *clusterState) rebalanceStores(
 			if store.StoreID != localStoreID && store.dimSummary[CPURate] >= overloadSlow &&
 				now.Sub(ss.overloadStartTime) < remoteStoreLeaseSheddingGraceDuration {
 				log.KvDistribution.VInfof(ctx, 2, "skipping remote store s%d: in lease shedding grace period", store.StoreID)
-				shouldContinue = true
-				break
+				return false, true
 			}
 			// If the node is cpu overloaded, or the store/node is not fdOK, exclude
 			// the other stores on this node from receiving replicas shed by this
@@ -555,8 +550,7 @@ func (cs *clusterState) rebalanceStores(
 					rangeID, removeTarget.StoreID, addTarget.StoreID, changes[len(changes)-1], ss.adjusted.load, targetSS.adjusted.load)
 				if rangeMoveCount >= maxRangeMoveCount {
 					log.KvDistribution.VInfof(ctx, 2, "s%d has reached max range move count %d: mma returning with %d stores left in shedding stores", store.StoreID, maxRangeMoveCount, len(sheddingStores)-(idx+1))
-					shouldReturnEarly = true
-					break
+					return true, false
 				}
 				doneShedding = ss.maxFractionPendingDecrease >= maxFractionPendingThreshold
 				if doneShedding {
@@ -572,10 +566,10 @@ func (cs *clusterState) rebalanceStores(
 			// rebalancing to work well is not in scope.
 			if doneShedding {
 				log.KvDistribution.VInfof(ctx, 2, "store s%d is done shedding, moving to next store", store.StoreID)
-				shouldContinue = true
-				break
+				return false, true
 			}
-		}
+			return false, false
+		}()
 		if shouldReturnEarly {
 			return changes
 		}