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)