git: avoid leaking lock files on cancellation

Signed-off-by: Tonis Tiigi <tonistiigi@gmail.com>

source/git/gitsource.go

@@ -248,6 +248,9 @@ func (gs *gitSourceHandler) Snapshot(ctx context.Context) (out cache.ImmutableRe
 	}
 
 	if doFetch {
+		// make sure no old lock files have leaked
+		os.RemoveAll(filepath.Join(gitDir, "shallow.lock"))
+
 		args := []string{"fetch"}
 		if !isCommitSHA(ref) { // TODO: find a branch from ls-remote?
 			args = append(args, "--depth=1", "--no-tags")

source/git/gitsource_unix.go

@@ -6,6 +6,7 @@ import (
 	"context"
 	"os/exec"
 	"syscall"
+	"time"
 )
 
 func runProcessGroup(ctx context.Context, cmd *exec.Cmd) error {
@@ -17,7 +18,14 @@ func runProcessGroup(ctx context.Context, cmd *exec.Cmd) error {
 	go func() {
 		select {
 		case <-ctx.Done():
-			syscall.Kill(-cmd.Process.Pid, syscall.SIGKILL)
+			syscall.Kill(-cmd.Process.Pid, syscall.SIGTERM)
+			go func() {
+				select {
+				case <-waitDone:
+				case <-time.After(10 * time.Second):
+					syscall.Kill(-cmd.Process.Pid, syscall.SIGKILL)
+				}
+			}()
 		case <-waitDone:
 		}
 	}()