lockfiles

NU/cmd/nu/nu.go

@@ -12,6 +12,7 @@ import (
 	"net/http"
 	"net/url"
 	"os"
+	"path/filepath"
 	"strings"
 	"time"
 )
@@ -71,6 +72,12 @@ func main() {
 		}
 	}()
 
+	myLock := "/net/corpora/nlnieuws/NU/lock"
+	mkLock(myLock)
+	defer func() {
+		_ = os.Remove(myLock)
+	}()
+
 	resp, err := http.Get("https://www.nu.nl/rss")
 	p(err)
 	body, err := io.ReadAll(resp.Body)
@@ -253,3 +260,16 @@ func doArticle(filename string, url string, timestamp time.Time, needUpdate bool
 func fixSpace(s string) string {
 	return strings.Join(strings.Fields(s), " ")
 }
+
+func mkLock(filename string) {
+	pid := os.Getpid()
+	link := fmt.Sprintf("%s.%d", filepath.Base(filename), pid)
+	p(os.Symlink(link, filename))
+
+	name, err := os.Readlink(filename)
+	p(err)
+
+	if name != link {
+		p(fmt.Errorf("wrong lock name %q, should be %q", name, link))
+	}
+}