--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/graal/com.oracle.graal.debug/src/com/oracle/graal/debug/Fingerprint.java	Tue Jan 20 16:22:11 2015 +0100
@@ -0,0 +1,132 @@
+/*
+ * Copyright (c) 2015, Oracle and/or its affiliates. All rights reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+package com.oracle.graal.debug;
+
+import java.util.*;
+import java.util.stream.*;
+
+/**
+ * Facility for fingerprinting execution.
+ */
+public class Fingerprint implements AutoCloseable {
+
+    private static final String ENABLED_PROPERTY_NAME = "graal.fingerprint";
+
+    /**
+     * Determines whether fingerprinting is enabled. This is set by the
+     * {@value #ENABLED_PROPERTY_NAME} system property when this class is initialized.
+     */
+    public static final boolean ENABLED = Boolean.getBoolean(ENABLED_PROPERTY_NAME);
+
+    private static final ThreadLocal<Fingerprint> current = ENABLED ? new ThreadLocal<>() : null;
+
+    private final List<String> events;
+    private int index;
+
+    /**
+     * Creates an object to record a fingerprint.
+     */
+    public Fingerprint() {
+        events = new ArrayList<>();
+        index = -1;
+    }
+
+    /**
+     * Creates an object to verify execution matches a given fingerprint.
+     *
+     * @param toVerifyAgainst the fingerprint to verify against
+     */
+    public Fingerprint(Fingerprint toVerifyAgainst) {
+        this.events = toVerifyAgainst.events;
+        index = 0;
+    }
+
+    /**
+     * Starts fingerprint recording or verification for the current thread. At most one fingerprint
+     * object can be active for any thread.
+     */
+    public Fingerprint open() {
+        if (ENABLED) {
+            assert current.get() == null;
+            current.set(this);
+            return this;
+        }
+        return null;
+    }
+
+    /**
+     * Finishes fingerprint recording or verification for the current thread.
+     */
+    public void close() {
+        if (ENABLED) {
+            assert current.get() == this;
+            current.set(null);
+        }
+    }
+
+    private static final int BREAKPOINT_EVENT = Integer.getInteger(ENABLED_PROPERTY_NAME + ".breakpointEvent", -1);
+
+    /**
+     * Submits an execution event for the purpose of recording or verifying a fingerprint. This must
+     * only be called if {@link #ENABLED} is {@code true}.
+     */
+    public static void submit(String format, Object... args) {
+        assert ENABLED : "fingerprinting must be enabled (-D" + ENABLED_PROPERTY_NAME + "=true)";
+        Fingerprint fingerprint = current.get();
+        if (fingerprint != null) {
+            int eventId = fingerprint.nextEventId();
+            if (eventId == BREAKPOINT_EVENT) {
+                // Set IDE breakpoint on the following line and set the relevant
+                // system property to debug a fingerprint verification error.
+                System.console();
+            }
+            fingerprint.event(String.format(eventId + ": " + format, args));
+        }
+    }
+
+    private int nextEventId() {
+        return index == -1 ? events.size() : index;
+    }
+
+    private static final int MAX_EVENT_TAIL_IN_ERROR_MESSAGE = Integer.getInteger("graal.fingerprint.errorEventTailLength", 50);
+
+    private String tail() {
+        int start = Math.max(index - MAX_EVENT_TAIL_IN_ERROR_MESSAGE, 0);
+        return events.subList(start, index).stream().collect(Collectors.joining(String.format("%n")));
+    }
+
+    private void event(String entry) {
+        if (index == -1) {
+            events.add(entry);
+        } else {
+            if (index > events.size()) {
+                throw new InternalError(String.format("%s%nOriginal fingerprint limit reached", tail()));
+            }
+            String l = events.get(index);
+            if (!l.equals(entry)) {
+                throw new InternalError(String.format("%s%nFingerprint differs at event %d%nexpected: %s%n  actual: %s", tail(), index, l, entry));
+            }
+            index++;
+        }
+    }
+}