Add parallelism limit

cmd/gomobile/bind.go

@@ -126,10 +126,13 @@ func runBind(cmd *command) error {
 	case isAndroidPlatform(targets[0].platform):
 		return goAndroidBind(gobind, pkgs, targets)
 	case isApplePlatform(targets[0].platform):
+		if buildWorkerError := validateBuildWorkers(buildWorkers); buildWorkerError != nil {
+			return buildWorkerError
+		}
 		if !xcodeAvailable() {
 			return fmt.Errorf("-target=%q requires Xcode", buildTarget)
 		}
-		return goAppleBind(gobind, pkgs, targets)
+		return goAppleBind(gobind, pkgs, targets, buildWorkers)
 	default:
 		return fmt.Errorf(`invalid -target=%q`, buildTarget)
 	}
@@ -321,3 +324,11 @@ func areGoModulesUsed() (bool, error) {
 	}
 	return true, nil
 }
+
+func validateBuildWorkers(workers int) error {
+	if workers < 1 {
+		return fmt.Errorf("invalid workers %d: must be >= 1", workers)
+	} else {
+		return nil
+	}
+}

cmd/gomobile/bind_iosapp.go

@@ -23,7 +23,7 @@ type archBuildResult struct {
 	frameworkPath string
 }
 
-func goAppleBind(gobind string, pkgs []*packages.Package, targets []targetInfo) error {
+func goAppleBind(gobind string, pkgs []*packages.Package, targets []targetInfo, buildWorkers int) error {
 	var name string
 	var title string
 
@@ -55,15 +55,20 @@ func goAppleBind(gobind string, pkgs []*packages.Package, targets []targetInfo)
 	var waitGroup sync.WaitGroup
 	waitGroup.Add(len(targets))
 
-	var parallelBuildError error
+	var parallelBuildErrorBuffer = make(chan error, len(targets))
+	semophore := make(chan struct{}, buildWorkers)
 
 	for _, target := range targets {
 		go func(target targetInfo) {
-			defer waitGroup.Done()
+			semophore <- struct{}{}
+			defer func() {
+				<-semophore
+				waitGroup.Done()
+			}()
 
 			buildResult, err := buildTargetArch(target, gobind, pkgs, title, name, modulesUsed)
 			if err != nil {
-				parallelBuildError = fmt.Errorf("cannot build %s [%s]: %v", target.platform, target.arch, err)
+				parallelBuildErrorBuffer <- fmt.Errorf("cannot build %s [%s]: %v", target.platform, target.arch, err)
 				return
 			}
 
@@ -75,9 +80,10 @@ func goAppleBind(gobind string, pkgs []*packages.Package, targets []targetInfo)
 	}
 
 	waitGroup.Wait()
+	close(parallelBuildErrorBuffer)
 
-	if parallelBuildError != nil {
-		return parallelBuildError
+	for buildErr := range parallelBuildErrorBuffer {
+		return buildErr
 	}
 
 	// Finally combine all frameworks to an XCFramework

cmd/gomobile/build.go

@@ -14,6 +14,7 @@ import (
 	"os"
 	"os/exec"
 	"regexp"
+	"runtime"
 	"strconv"
 	"strings"
 
@@ -243,6 +244,7 @@ var (
 	buildTarget     string      // -target
 	buildTrimpath   bool        // -trimpath
 	buildWork       bool        // -work
+	buildWorkers    int         // -j
 	buildBundleID   string      // -bundleid
 	buildIOSVersion string      // -iosversion
 	buildAndroidAPI int         // -androidapi
@@ -262,6 +264,7 @@ func addBuildFlags(cmd *command) {
 	cmd.flag.BoolVar(&buildI, "i", false, "")
 	cmd.flag.BoolVar(&buildTrimpath, "trimpath", false, "")
 	cmd.flag.Var(&buildTags, "tags", "")
+	cmd.flag.IntVar(&buildWorkers, "j", runtime.NumCPU(), "")
 }
 
 func addBuildFlagsNVXWork(cmd *command) {