lockfiles

NieuwsNL/cmd/nieuwsnl/nieuwsnl.go

@@ -11,6 +11,7 @@ import (
 	"net/http"
 	"net/url"
 	"os"
+	"path/filepath"
 	"strings"
 	"time"
 )
@@ -62,6 +63,12 @@ func main() {
 		}
 	}()
 
+	myLock := "/net/corpora/nlnieuws/NieuwsNL/lock"
+	mkLock(myLock)
+	defer func() {
+		_ = os.Remove(myLock)
+	}()
+
 	req, err := http.NewRequest("GET", "https://nieuws.nl/sitemap/news.xml", nil)
 	p(err)
 	req.Header.Set("User-Agent", agent)
@@ -230,3 +237,16 @@ func addEnd(s string) string {
 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))
+	}
+}