--- loncom/LONCAPA.pm	2010/06/15 05:31:43	1.30
+++ loncom/LONCAPA.pm	2011/05/14 16:12:53	1.31
@@ -1,7 +1,7 @@
 # The LearningOnline Network
 # Base routines
 #
-# $Id: LONCAPA.pm,v 1.30 2010/06/15 05:31:43 raeburn Exp $
+# $Id: LONCAPA.pm,v 1.31 2011/05/14 16:12:53 raeburn Exp $
 #
 # Copyright Michigan State University Board of Trustees
 #
@@ -155,6 +155,47 @@ sub clean_handle {
     return $handle;
 }
 
+#
+# -- Ensure another process for same filesystem action is not running.
+#    lond uses for: apachereload; loncron uses for: lciptables
+#
+
+sub try_to_lock {
+    my ($lockfile)=@_;
+    my $currentpid;
+    my $lastpid;
+    # Do not manipulate lock file as root
+    if ($>==0) {
+        return 0;
+    }
+    # Try to generate lock file.
+    # Wait 3 seconds.  If same process id is in
+    # lock file, then assume lock file is stale, and
+    # go ahead.  If process id's fluctuate, try
+    # for a maximum of 10 times.
+    for (0..10) {
+        if (-e $lockfile) { 
+            open(LOCK,"<$lockfile");
+            $currentpid=<LOCK>;
+            close LOCK;
+            if ($currentpid==$lastpid) {
+                last;
+            }
+            sleep 3;
+            $lastpid=$currentpid;
+        } else {
+            last;
+        }
+        if ($_==10) {
+            return 0;
+        }
+    }
+    open(LOCK,">$lockfile");
+    print LOCK $$;
+    close LOCK;
+    return 1;
+}
+
 # -------------------------------------------- Return path to profile directory
 
 sub propath {