From a1faca26314b34b592f391baa5bc4d014bc1ef2c Mon Sep 17 00:00:00 2001
From: "Richard M. Stallman" <rms@gnu.org>
Date: Thu, 12 Sep 1996 17:29:17 +0000
Subject: [PATCH] (lock_superlock): Delete superlock file if it stayed locked
 for 20 seconds.

---
 src/filelock.c | 54 ++++++++++++++++++++++++++++++++++++++++----------
 1 file changed, 43 insertions(+), 11 deletions(-)

diff --git a/src/filelock.c b/src/filelock.c
index 5393867063c..6c1b6b2a1c4 100644
--- a/src/filelock.c
+++ b/src/filelock.c
@@ -353,32 +353,64 @@ lock_superlock (lfname)
 {
   register int i, fd;
   DIR *lockdir;
+  struct stat first_stat, last_stat;
 
-  for (i = -20; i < 0 && (fd = open (superlock_file,
-				     O_WRONLY | O_EXCL | O_CREAT, 0666)) < 0;
+  for (i = -20; i < 0;
        i++)
     {
+      fd = open (superlock_file,
+		 O_WRONLY | O_EXCL | O_CREAT, 0666);
+
+      /* If we succeeded in creating the superlock, we win.
+	 Fill in our info and return.  */
+      if (fd >= 0)
+	{
+#ifdef USG
+	  chmod (superlock_file, 0666);
+#else
+	  fchmod (fd, 0666);
+#endif
+	  write (fd, lfname, strlen (lfname));
+	  close (fd);
+	  return;
+	}
+
+      /* If the problem is not just that it is already locked,
+	 give up.  */
       if (errno != EEXIST)
 	return;
 
+      message ("Superlock file exists, retrying...");
+
+      if (i == -20)
+	stat (superlock_file, &first_stat);
+
+      if (i == -1)
+	stat (superlock_file, &last_stat);
+
       /* This seems to be necessary to prevent Emacs from hanging when the
 	 competing process has already deleted the superlock, but it's still
 	 in the NFS cache.  So we force NFS to synchronize the cache.  */
-      if (lockdir = opendir (lock_dir))
+      lockdir = opendir (lock_dir);
+
+      if (lockdir)
 	closedir (lockdir);
 
       sleep (1);
     }
-  if (fd >= 0)
+
+  if (first_stat.st_ctime == last_stat.st_ctime)
     {
-#ifdef USG
-      chmod (superlock_file, 0666);
-#else
-      fchmod (fd, 0666);
-#endif
-      write (fd, lfname, strlen (lfname));
-      close (fd);
+      int value;
+      value = unlink (superlock_file);
+
+      if (value != -1)
+	message ("Superlock file deleted");
+      else
+	message ("Failed to delete superlock file");
     }
+  else
+    message ("Giving up on the superlock file");
 }
 
 void
-- 
2.39.2