--- Src/hist.c	14 Apr 2008 13:42:53 -0000	1.74
+++ Src/hist.c	17 Apr 2008 16:12:04 -0000
@@ -2330,6 +2330,36 @@ savehistfile(char *fn, int err, int writ
     unlockhistfile(fn);
 }
 
+#ifdef HAVE_FCNTL_H
+static int flock_fd = -1;
+
+static int
+flockhistfile(char *fn, int keep_trying)
+{
+    struct flock lck;
+    int ctr = keep_trying ? 9 : 0;
+
+    if ((flock_fd = open(unmeta(fn), O_RDWR | O_NOCTTY)) < 0)
+	return errno == ENOENT; /* "successfully" locked missing file */
+
+    lck.l_type = F_WRLCK;
+    lck.l_whence = SEEK_SET;
+    lck.l_start = 0;
+    lck.l_len = 0;  /* lock the whole file */
+
+    while (fcntl(flock_fd, F_SETLKW, &lck) == -1) {
+	if (--ctr < 0) {
+	    close(flock_fd);
+	    flock_fd = -1;
+	    return 0;
+	}
+	sleep(1);
+    }
+
+    return 1;
+}
+#endif
+
 static int lockhistct;
 
 /**/
@@ -2340,6 +2370,12 @@ lockhistfile(char *fn, int keep_trying)
 
     if (!fn && !(fn = getsparam("HISTFILE")))
 	return 0;
+
+#ifdef HAVE_FCNTL_H
+    if (isset(HISTFCNTLLOCK) && !lockhistct && !flockhistfile(fn, keep_trying))
+	return 0;
+#endif
+
     if (!lockhistct++) {
 	struct stat sb;
 	int fd;
@@ -2404,7 +2440,15 @@ lockhistfile(char *fn, int keep_trying)
 #endif /* not HAVE_LINK */
 	free(lockfile);
     }
-    return ct != lockhistct;
+
+    if (ct == lockhistct) {
+#ifdef HAVE_FCNTL_H
+	close(flock_fd);
+	flock_fd = -1;
+#endif
+	return 0;
+    }
+    return 1;
 }
 
 /* Unlock the history file if this corresponds to the last nested lock
@@ -2428,6 +2472,12 @@ unlockhistfile(char *fn)
 	sprintf(lockfile, "%s.LOCK", fn);
 	unlink(lockfile);
 	free(lockfile);
+#ifdef HAVE_FCNTL_H
+	if (flock_fd >= 0) {
+	    close(flock_fd);
+	    flock_fd = -1;
+	}
+#endif
     }
 }