[DECO-94] Execute uploads in parallel instead of sequentailly (#81)

Tested manually

Upload seems fast enough, delete API calls though have a much longer
turn around times

Additional optimizations that can be done if/when the need arises:
1. First time upload can be done using zip batching of the files


https://user-images.githubusercontent.com/88374338/192783332-9b2b19bc-d6c4-4a66-8dbc-e78287e6af1a.mov

cmd/sync/watchdog.go

@@ -17,6 +17,7 @@ import (
 	"github.com/databricks/databricks-sdk-go/databricks/client"
 	"github.com/databricks/databricks-sdk-go/service/workspace"
 	"github.com/databricks/databricks-sdk-go/workspaces"
+	"golang.org/x/sync/errgroup"
 )
 
 type watchdog struct {
@@ -26,6 +27,10 @@ type watchdog struct {
 	failure error // data race? make channel?
 }
 
+// See https://docs.databricks.com/resources/limits.html#limits-api-rate-limits for per api
+// rate limits
+const MaxRequestsInFlight = 20
+
 func putFile(ctx context.Context, path string, content io.Reader) error {
 	wsc := project.Get(ctx).WorkspacesClient()
 	// workspace mkdirs is idempotent
@@ -42,32 +47,57 @@ func putFile(ctx context.Context, path string, content io.Reader) error {
 
 func getRemoteSyncCallback(ctx context.Context, root, remoteDir string, wsc *workspaces.WorkspacesClient) func(localDiff diff) error {
 	return func(d diff) error {
-		for _, filePath := range d.delete {
+
+		// Abstraction over wait groups which allows you to get the errors
+		// returned in goroutines
+		var g errgroup.Group
+
+		// Allow MaxRequestLimit maxiumum concurrent api calls
+		g.SetLimit(MaxRequestsInFlight)
+
+		for _, fileName := range d.delete {
+			// Copy of fileName created to make this safe for concurrent use.
+			// directly using fileName can cause race conditions since the loop
+			// might iterate over to the next fileName before the go routine function
+			// is evaluated
+			localFileName := fileName
+			g.Go(func() error {
 				err := wsc.Workspace.Delete(ctx,
 					workspace.Delete{
-					Path:      path.Join(remoteDir, filePath),
+						Path:      path.Join(remoteDir, localFileName),
 						Recursive: true,
 					},
 				)
 				if err != nil {
 					return err
 				}
-			log.Printf("[INFO] Deleted %s", filePath)
+				log.Printf("[INFO] Deleted %s", localFileName)
+				return nil
+			})
 		}
-		for _, filePath := range d.put {
-			f, err := os.Open(filepath.Join(root, filePath))
+		for _, fileName := range d.put {
+			localFileName := fileName
+			g.Go(func() error {
+				f, err := os.Open(filepath.Join(root, localFileName))
 				if err != nil {
 					return err
 				}
-			err = putFile(ctx, path.Join(remoteDir, filePath), f)
+				err = putFile(ctx, path.Join(remoteDir, localFileName), f)
 				if err != nil {
-				return fmt.Errorf("failed to upload file: %s", err) // TODO: fmt.Errorf
+					return fmt.Errorf("failed to upload file: %s", err)
 				}
 				err = f.Close()
 				if err != nil {
-				return err // TODO: fmt.Errorf
+					return err
 				}
-			log.Printf("[INFO] Uploaded %s", filePath)
+				log.Printf("[INFO] Uploaded %s", localFileName)
+				return nil
+			})
+		}
+		// wait for goroutines to finish and return first non-nil error return
+		// if any
+		if err := g.Wait(); err != nil {
+			return err
 		}
 		return nil
 	}

go.mod

@@ -17,6 +17,8 @@ require (
 	gopkg.in/ini.v1 v1.67.0 // Apache 2.0
 )
 
+require golang.org/x/sync v0.0.0-20220513210516-0976fa681c29
+
 require (
 	cloud.google.com/go/compute v1.6.1 // indirect
 	github.com/chzyer/readline v0.0.0-20180603132655-2972be24d48e // indirect

go.sum

@@ -354,6 +354,7 @@ golang.org/x/sync v0.0.0-20200625203802-6e8e738ad208/go.mod h1:RxMgew5VJxzue5/jJ
 golang.org/x/sync v0.0.0-20201020160332-67f06af15bc9/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
 golang.org/x/sync v0.0.0-20201207232520-09787c993a3a/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
 golang.org/x/sync v0.0.0-20210220032951-036812b2e83c/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
+golang.org/x/sync v0.0.0-20220513210516-0976fa681c29 h1:w8s32wxx3sY+OjLlv9qltkLU5yvJzxjjgiHWLjdIcw4=
 golang.org/x/sync v0.0.0-20220513210516-0976fa681c29/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
 golang.org/x/sys v0.0.0-20180830151530-49385e6e1522/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
 golang.org/x/sys v0.0.0-20181122145206-62eef0e2fa9b/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=