Clone different git repos in parallel via per-directory locks (#866)

Old `cloneLock` is a package-level `sync.Mutex` that serialized every action clone across all goroutines, regardless of target directory.
This PR replaces it with a `sync.Map` of per-directory mutexes keyed by `input.Dir`. Same-directory operations still serialize; different directories now clone in parallel.

Reviewed-on: https://gitea.com/gitea/act_runner/pulls/866
Reviewed-by: Lunny Xiao <xiaolunwen@gmail.com>
Co-authored-by: Zettat123 <zettat123@gmail.com>
Co-committed-by: Zettat123 <zettat123@gmail.com>

act/common/git/git.go

@@ -32,12 +32,21 @@ var (
 	githubHTTPRegex     = regexp.MustCompile(`^https?://.*github.com.*/(.+)/(.+?)(?:.git)?$`)
 	githubSSHRegex      = regexp.MustCompile(`github.com[:/](.+)/(.+?)(?:.git)?$`)
 
-	cloneLock sync.Mutex
+	cloneLocks sync.Map // key: clone target directory; value: *sync.Mutex
 
 	ErrShortRef = errors.New("short SHA references are not supported")
 	ErrNoRepo   = errors.New("unable to find git repo")
 )
 
+// acquireCloneLock returns an unlock function after locking the per-directory mutex for dir.
+// Only concurrent operations targeting the same directory are erialized; clones into different directories run in parallel.
+func acquireCloneLock(dir string) func() {
+	v, _ := cloneLocks.LoadOrStore(dir, &sync.Mutex{})
+	mu := v.(*sync.Mutex)
+	mu.Lock()
+	return mu.Unlock
+}
+
 type Error struct {
 	err    error
 	commit string
@@ -301,8 +310,7 @@ func NewGitCloneExecutor(input NewGitCloneExecutorInput) common.Executor {
 		logger.Infof("  \u2601  git clone '%s' # ref=%s", input.URL, input.Ref)
 		logger.Debugf("  cloning %s to %s", input.URL, input.Dir)
 
-		cloneLock.Lock()
-		defer cloneLock.Unlock()
+		defer acquireCloneLock(input.Dir)()
 
 		refName := plumbing.ReferenceName("refs/heads/" + input.Ref)
 		r, err := CloneIfRequired(ctx, refName, input, logger)

act/common/git/git_test.go

@@ -11,8 +11,10 @@ import (
 	"os/exec"
 	"path/filepath"
 	"strings"
+	"sync"
 	"syscall"
 	"testing"
+	"time"
 
 	log "github.com/sirupsen/logrus"
 	"github.com/stretchr/testify/assert"
@@ -303,3 +305,61 @@ func gitCmd(args ...string) error {
 	}
 	return nil
 }
+
+func TestAcquireCloneLock(t *testing.T) {
+	t.Run("same directory serializes", func(t *testing.T) {
+		dir := t.TempDir()
+
+		unlock1 := acquireCloneLock(dir)
+
+		secondAcquired := make(chan struct{})
+		go func() {
+			unlock := acquireCloneLock(dir)
+			close(secondAcquired)
+			unlock()
+		}()
+
+		select {
+		case <-secondAcquired:
+			t.Fatal("second acquire should block while first holds the lock")
+		case <-time.After(50 * time.Millisecond):
+		}
+
+		unlock1()
+
+		select {
+		case <-secondAcquired:
+		case <-time.After(time.Second):
+			t.Fatal("second acquire should proceed after first releases the lock")
+		}
+	})
+
+	t.Run("different directories do not block", func(t *testing.T) {
+		dirA := t.TempDir()
+		dirB := t.TempDir()
+
+		unlockA := acquireCloneLock(dirA)
+		defer unlockA()
+
+		done := make(chan struct{})
+		go func() {
+			unlock := acquireCloneLock(dirB)
+			unlock()
+			close(done)
+		}()
+
+		select {
+		case <-done:
+		case <-time.After(time.Second):
+			t.Fatal("acquire on a different directory must not block")
+		}
+	})
+
+	t.Run("same directory reuses the same mutex", func(t *testing.T) {
+		dir := t.TempDir()
+
+		v1, _ := cloneLocks.LoadOrStore(dir, &sync.Mutex{})
+		v2, _ := cloneLocks.LoadOrStore(dir, &sync.Mutex{})
+		require.Same(t, v1, v2)
+	})
+}