Rework `shell.EcBalance()`'s waitgroup code into a standalone type. (#6373)

Rework `shell.EcBalance()`'s waitgroup with errors code into a standalone type.

We'll re-use this for other EC jobs - for example, volume creation. Also fixes
potential concurrency issues when collecting error results.

weed/shell/command_ec_common.go

@@ -113,6 +113,50 @@ var (
 	getDefaultReplicaPlacement = _getDefaultReplicaPlacement
 )
 
+type ErrorWaitGroup struct {
+	parallelize bool
+	wg          *sync.WaitGroup
+	errors      []error
+	errorsMu    sync.Mutex
+}
+type ErrorWaitGroupTask func() error
+
+func (ewg *ErrorWaitGroup) Init() {
+	if ewg.wg != nil {
+		return
+	}
+	ewg.wg = &sync.WaitGroup{}
+	ewg.errors = nil
+}
+
+func (ewg *ErrorWaitGroup) Add(f ErrorWaitGroupTask) {
+	if ewg.wg == nil || !ewg.parallelize {
+		ewg.errors = append(ewg.errors, f())
+		return
+	}
+
+	ewg.wg.Add(1)
+	go func() {
+		err := f()
+		ewg.errorsMu.Lock()
+		ewg.errors = append(ewg.errors, err)
+		ewg.errorsMu.Unlock()
+		ewg.wg.Done()
+	}()
+}
+
+func (ewg *ErrorWaitGroup) Wait() error {
+	if ewg.wg != nil {
+		ewg.wg.Wait()
+	}
+
+	err := errors.Join(ewg.errors...)
+	ewg.wg = nil
+	ewg.errors = nil
+
+	return err
+}
+
 func _getDefaultReplicaPlacement(commandEnv *CommandEnv) (*super_block.ReplicaPlacement, error) {
 	var resp *master_pb.GetMasterConfigurationResponse
 	var err error
@@ -557,48 +601,8 @@ type ecBalancer struct {
 	ecNodes          []*EcNode
 	replicaPlacement *super_block.ReplicaPlacement
 	applyBalancing   bool
-	parallelize      bool
 
-	wg       *sync.WaitGroup
-	wgErrors []error
-}
-
-type ecBalancerTask func() error
-
-func (ecb *ecBalancer) wgInit() {
-	if ecb.wg != nil {
-		return
-	}
-	ecb.wg = &sync.WaitGroup{}
-	ecb.wgErrors = nil
-}
-
-func (ecb *ecBalancer) wgAdd(f ecBalancerTask) {
-	if ecb.wg == nil || !ecb.parallelize {
-		if err := f(); err != nil {
-			ecb.wgErrors = append(ecb.wgErrors, err)
-		}
-		return
-	}
-
-	ecb.wg.Add(1)
-	go func() {
-		if err := f(); err != nil {
-			ecb.wgErrors = append(ecb.wgErrors, err)
-		}
-		ecb.wg.Done()
-	}()
-}
-
-func (ecb *ecBalancer) wgWait() error {
-	if ecb.wg != nil {
-		ecb.wg.Wait()
-	}
-	err := errors.Join(ecb.wgErrors...)
-	ecb.wg = nil
-	ecb.wgErrors = nil
-
-	return err
+	ewg ErrorWaitGroup
 }
 
 func (ecb *ecBalancer) racks() map[RackId]*EcRack {
@@ -637,13 +641,13 @@ func (ecb *ecBalancer) balanceEcVolumes(collection string) error {
 func (ecb *ecBalancer) deleteDuplicatedEcShards(collection string) error {
 	vidLocations := ecb.collectVolumeIdToEcNodes(collection)
 
-	ecb.wgInit()
+	ecb.ewg.Init()
 	for vid, locations := range vidLocations {
-		ecb.wgAdd(func() error {
+		ecb.ewg.Add(func() error {
 			return ecb.doDeduplicateEcShards(collection, vid, locations)
 		})
 	}
-	return ecb.wgWait()
+	return ecb.ewg.Wait()
 }
 
 func (ecb *ecBalancer) doDeduplicateEcShards(collection string, vid needle.VolumeId, locations []*EcNode) error {
@@ -684,13 +688,13 @@ func (ecb *ecBalancer) balanceEcShardsAcrossRacks(collection string) error {
 	vidLocations := ecb.collectVolumeIdToEcNodes(collection)
 
 	// spread the ec shards evenly
-	ecb.wgInit()
+	ecb.ewg.Init()
 	for vid, locations := range vidLocations {
-		ecb.wgAdd(func() error {
+		ecb.ewg.Add(func() error {
 			return ecb.doBalanceEcShardsAcrossRacks(collection, vid, locations)
 		})
 	}
-	return ecb.wgWait()
+	return ecb.ewg.Wait()
 }
 
 func countShardsByRack(vid needle.VolumeId, locations []*EcNode) map[string]int {
@@ -792,7 +796,7 @@ func (ecb *ecBalancer) balanceEcShardsWithinRacks(collection string) error {
 	racks := ecb.racks()
 
 	// spread the ec shards evenly
-	ecb.wgInit()
+	ecb.ewg.Init()
 	for vid, locations := range vidLocations {
 
 		// see the volume's shards are in how many racks, and how many in each rack
@@ -811,12 +815,12 @@ func (ecb *ecBalancer) balanceEcShardsWithinRacks(collection string) error {
 			}
 			sourceEcNodes := rackEcNodesWithVid[rackId]
 			averageShardsPerEcNode := ceilDivide(rackToShardCount[rackId], len(possibleDestinationEcNodes))
-			ecb.wgAdd(func() error {
+			ecb.ewg.Add(func() error {
 				return ecb.doBalanceEcShardsWithinOneRack(averageShardsPerEcNode, collection, vid, sourceEcNodes, possibleDestinationEcNodes)
 			})
 		}
 	}
-	return ecb.wgWait()
+	return ecb.ewg.Wait()
 }
 
 func (ecb *ecBalancer) doBalanceEcShardsWithinOneRack(averageShardsPerEcNode int, collection string, vid needle.VolumeId, existingLocations, possibleDestinationEcNodes []*EcNode) error {
@@ -847,13 +851,13 @@ func (ecb *ecBalancer) doBalanceEcShardsWithinOneRack(averageShardsPerEcNode int
 
 func (ecb *ecBalancer) balanceEcRacks() error {
 	// balance one rack for all ec shards
-	ecb.wgInit()
+	ecb.ewg.Init()
 	for _, ecRack := range ecb.racks() {
-		ecb.wgAdd(func() error {
+		ecb.ewg.Add(func() error {
 			return ecb.doBalanceEcRack(ecRack)
 		})
 	}
-	return ecb.wgWait()
+	return ecb.ewg.Wait()
 }
 
 func (ecb *ecBalancer) doBalanceEcRack(ecRack *EcRack) error {
@@ -1067,7 +1071,10 @@ func EcBalance(commandEnv *CommandEnv, collections []string, dc string, ecReplic
 		ecNodes:          allEcNodes,
 		replicaPlacement: ecReplicaPlacement,
 		applyBalancing:   applyBalancing,
-		parallelize:      parallelize,
+
+		ewg: ErrorWaitGroup{
+			parallelize: parallelize,
+		},
 	}
 
 	for _, c := range collections {