--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/jdk.jfr/share/classes/jdk/jfr/internal/consumer/ConstantMap.java	Wed Oct 30 19:43:52 2019 +0100
@@ -0,0 +1,184 @@
+/*
+ * Copyright (c) 2016, 2019, 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.  Oracle designates this
+ * particular file as subject to the "Classpath" exception as provided
+ * by Oracle in the LICENSE file that accompanied this code.
+ *
+ * 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 jdk.jfr.internal.consumer;
+
+import jdk.jfr.internal.LongMap;
+
+/**
+ * Holds mapping between a set of keys and their corresponding object.
+ *
+ * If the type is a known type, i.e. {@link RecordedThread}, an
+ * {@link ObjectFactory} can be supplied which will instantiate a typed object.
+ */
+final class ConstantMap {
+
+    private static final int RESOLUTION_FINISHED = 0;
+    private static final int RESOLUTION_STARTED = 1;
+    public static final ConstantMap EMPTY = new ConstantMap();
+
+    // A temporary placeholder, so objects can
+    // reference themselves (directly, or indirectly),
+    // when making a transition from numeric id references
+    // to normal Java references.
+    private final static class Reference {
+        private final long key;
+        private final ConstantMap pool;
+
+        Reference(ConstantMap pool, long key) {
+            this.pool = pool;
+            this.key = key;
+        }
+
+        Object resolve() {
+            return pool.get(key);
+        }
+
+        public String toString() {
+            return "ref: " + pool.name + "[" + key + "]";
+        }
+    }
+
+    final ObjectFactory<?> factory;
+    final String name;
+
+    private final LongMap<Object> objects;
+
+    private boolean resolving;
+    private boolean allResolved;
+
+    private ConstantMap() {
+        this(null, "<empty>");
+        allResolved = true;
+    }
+
+    ConstantMap(ObjectFactory<?> factory, String name) {
+        this.name = name;
+        this.objects = new LongMap<>(2);
+        this.factory = factory;
+    }
+
+    Object get(long id) {
+        // fast path, all objects in pool resolved
+        if (allResolved) {
+            return objects.get(id);
+        }
+        // referenced from a pool, deal with this later
+        if (!resolving) {
+            return new Reference(this, id);
+        }
+
+        // should always have a value
+        Object value = objects.get(id);
+        if (value == null) {
+            // unless is 0 which is used to represent null
+            if (id == 0) {
+                return null;
+            }
+            throw new InternalError("Missing object id=" + id + " in pool " + name + ". All ids should reference object");
+        }
+
+        // id is resolved (but not the whole pool)
+        if (objects.isSetId(id, RESOLUTION_FINISHED)) {
+            return value;
+        }
+
+        // resolving ourself, abort to avoid infinite recursion
+        if (objects.isSetId(id, RESOLUTION_STARTED)) {
+            return null;
+        }
+
+        // mark id as STARTED if we should
+        // come back during object resolution
+        objects.setId(id, RESOLUTION_STARTED);
+
+        // resolve object!
+        Object resolved = resolve(value);
+
+        // mark id as FINISHED
+        objects.setId(id, RESOLUTION_FINISHED);
+
+        // if a factory exists, convert to RecordedThread.
+        // RecordedClass etc. and store back results
+        if (factory != null) {
+            Object factorized = factory.createObject(id, resolved);
+            objects.put(id, factorized);
+            return factorized;
+        } else {
+            objects.put(id, resolved);
+            return resolved;
+        }
+    }
+
+    private static Object resolve(Object o) {
+        if (o instanceof Reference) {
+            return resolve(((Reference) o).resolve());
+        }
+        if (o != null && o.getClass().isArray()) {
+            final Object[] array = (Object[]) o;
+            for (int i = 0; i < array.length; i++) {
+                Object element = array[i];
+                array[i] = resolve(element);
+            }
+            return array;
+        }
+        return o;
+    }
+
+    public void resolve() {
+        objects.forEachKey(k -> get(k));
+    }
+
+    public void put(long key, Object value) {
+        objects.put(key, value);
+    }
+
+    public void setResolving() {
+        resolving = true;
+        allResolved = false;
+    }
+
+    public void setResolved() {
+        allResolved = true;
+        resolving = false;
+    }
+
+    public String getName() {
+        return name;
+    }
+
+    public Object getResolved(long id) {
+        return objects.get(id);
+    }
+
+    public void putResolved(long id, Object object) {
+        objects.put(id, object);
+        objects.setId(id, RESOLUTION_FINISHED);
+    }
+
+    public void setAllResolved(boolean allResolved) {
+        this.allResolved = allResolved;
+    }
+}