prevent multiple instances in same namespace

internal/p9/server/server.go

@@ -34,6 +34,7 @@ import (
 	"denote/internal/disk"
 	"denote/pkg/encoding/results"
 	"denote/pkg/metadata"
+	"errors"
 	"fmt"
 	"io"
 	"net"
@@ -41,6 +42,7 @@ import (
 	"regexp"
 	"strings"
 	"sync"
+	"syscall"
 	"time"
 
 	"9fans.net/go/plan9"
@@ -165,14 +167,36 @@ func StartServer(initialData metadata.Results, denoteDir string, callbacks Callb
 
 	sockPath := ns + "/denote"
 
-	// Remove old socket if it exists
+	// Try to create Unix domain socket listener
-	os.Remove(sockPath)
+	// Use stale socket detection like acme (see /usr/local/plan9/src/lib9/announce.c)
+	var listener net.Listener
+	var err error
+	for attempts := 0; attempts < 2; attempts++ {
+		listener, err = net.Listen("unix", sockPath)
+		if err == nil {
+			break // Successfully bound to socket
+		}
 
-	// Create Unix domain socket listener
+		// Check if error is "address already in use"
-	listener, err := net.Listen("unix", sockPath)
+		if errors.Is(err, syscall.EADDRINUSE) {
-	if err != nil {
+			// Try to connect to see if socket is live or stale
+			conn, dialErr := net.Dial("unix", sockPath)
+			if dialErr == nil {
+				// Connection succeeded - another instance is running
+				conn.Close()
+				return fmt.Errorf("Denote already running in this namespace")
+			}
+			// Connection failed - socket is stale, remove it and retry
+			os.Remove(sockPath)
+			continue
+		}
+
+		// Some other error
 		return fmt.Errorf("failed to listen on socket: %w", err)
 	}
+	if err != nil {
+		return fmt.Errorf("failed to listen on socket after cleanup: %w", err)
+	}
 
 	// Start accepting connections in background
 	go srv.acceptLoop(listener)

main.go

@@ -243,14 +243,25 @@ func main() {
 
 	// 9p server startup with pre-loaded data and callbacks
 	if err := p9server.StartServer(notes, denoteDir, callbacks); err != nil {
-		fmt.Fprintf(os.Stderr, "warning: failed to start fileserver: %v\n", err)
+		log.Fatal(err)
 	}
 
 	// start acme log watcher
 	go disk.WatchAcmeLog()
 
-	// open window
+	// open window - look for existing /Denote/ window across all processes
-	if w = acme.Show(wname); w == nil {
+	if wins, err := acme.Windows(); err == nil {
+		for _, winInfo := range wins {
+			if winInfo.Name == wname {
+				// Found existing window, open it
+				if w, err = acme.Open(winInfo.ID, nil); err == nil {
+					break
+				}
+			}
+		}
+	}
+	// If no existing window found, create new one
+	if w == nil {
 		if w, err = acme.New(); err != nil {
 			log.Fatal(err)
 		}