--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/graal/com.oracle.truffle.ruby.nodes/src/com/oracle/truffle/ruby/nodes/debug/RubyTraceProbe.java	Mon Feb 10 03:39:21 2014 +0000
@@ -0,0 +1,49 @@
+/*
+ * Copyright (c) 2013, 2014 Oracle and/or its affiliates. All rights reserved. This
+ * code is released under a tri EPL/GPL/LGPL license. You can use it,
+ * redistribute it and/or modify it under the terms of the:
+ *
+ * Eclipse Public License version 1.0
+ * GNU General Public License version 2
+ * GNU Lesser General Public License version 2.1
+ */
+package com.oracle.truffle.ruby.nodes.debug;
+
+import com.oracle.truffle.api.*;
+import com.oracle.truffle.api.frame.*;
+import com.oracle.truffle.api.nodes.*;
+import com.oracle.truffle.ruby.runtime.*;
+import com.oracle.truffle.ruby.runtime.subsystems.*;
+
+/**
+ * A "trace" probe that has no runtime cost until activated, at which time it invokes a trace
+ * message.
+ */
+public final class RubyTraceProbe extends RubyProbe {
+
+    private final Assumption notTracingAssumption;
+
+    @CompilerDirectives.CompilationFinal private boolean tracingEverEnabled = false;
+
+    public RubyTraceProbe(RubyContext context) {
+        super(context, false);
+        this.notTracingAssumption = context.getTraceManager().getNotTracingAssumption();
+    }
+
+    @Override
+    public void enter(Node astNode, VirtualFrame frame) {
+        if (!tracingEverEnabled) {
+            try {
+                notTracingAssumption.check();
+            } catch (InvalidAssumptionException e) {
+                tracingEverEnabled = true;
+            }
+        }
+        final TraceManager traceManager = context.getTraceManager();
+        if (tracingEverEnabled && traceManager.hasTraceProc()) {
+            final SourceSection sourceSection = astNode.getEncapsulatingSourceSection();
+            traceManager.trace("line", sourceSection.getSource().getName(), sourceSection.getStartLine(), 0, null, null);
+        }
+    }
+
+}