diff -r 2c3cc4b01880 -r c16ac7a2eba4 src/jdk.jfr/share/classes/jdk/jfr/internal/LongMap.java
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/jdk.jfr/share/classes/jdk/jfr/internal/LongMap.java	Wed Oct 30 19:43:52 2019 +0100
@@ -0,0 +1,257 @@
+/*
+ * Copyright (c) 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;
+
+import java.util.BitSet;
+import java.util.function.Consumer;
+import java.util.function.LongConsumer;
+
+@SuppressWarnings("unchecked")
+public final class LongMap<T> {
+    private static final int MAXIMUM_CAPACITY = 1 << 30;
+    private static final long[] EMPTY_KEYS = new long[0];
+    private static final Object[] EMPTY_OBJECTS = new Object[0];
+    private static final int DEFAULT_SIZE = 32;
+    private static final Object NULL_OBJECT = new Object();
+
+    private final int bitCount;
+    private BitSet bitSet;
+    private long[] keys = EMPTY_KEYS;
+    private T[] objects = (T[]) EMPTY_OBJECTS;
+    private int count;
+    private int shift;
+
+    public LongMap() {
+        this.bitCount = 0;
+    }
+
+    public LongMap(int markBits) {
+        this.bitCount = markBits;
+        this.bitSet = new BitSet();
+    }
+
+    // Should be 2^n
+    private void initialize(int capacity) {
+        keys = new long[capacity];
+        objects = (T[]) new Object[capacity];
+        shift = 64 - (31 - Integer.numberOfLeadingZeros(capacity));
+    }
+
+    public void claimBits() {
+        // flip last bit back and forth to make bitset expand to max size
+        int lastBit = bitSetIndex(objects.length - 1, bitCount -1);
+        bitSet.flip(lastBit);
+        bitSet.flip(lastBit);
+    }
+
+    public void setId(long id, int bitIndex) {
+        int bitSetIndex = bitSetIndex(tableIndexOf(id), bitIndex);
+        bitSet.set(bitSetIndex, true);
+    }
+
+    public void clearId(long id, int bitIndex) {
+        int bitSetIndex = bitSetIndex(tableIndexOf(id), bitIndex);
+        bitSet.set(bitSetIndex, false);
+    }
+
+    public boolean isSetId(long id, int bitIndex) {
+        int bitSetIndex = bitSetIndex(tableIndexOf(id), bitIndex);
+        return bitSet.get(bitSetIndex);
+    }
+
+    private int bitSetIndex(int tableIndex, int bitIndex) {
+        return bitCount * tableIndex + bitIndex;
+    }
+
+    private int tableIndexOf(long id) {
+        int index = index(id);
+        while (true) {
+            if (objects[index] == null) {
+                throw new InternalError("Unknown id");
+            }
+            if (keys[index] == id) {
+                return index;
+            }
+            index++;
+            if (index == keys.length) {
+                index = 0;
+            }
+        }
+    }
+
+    public boolean hasKey(long id) {
+        int index = index(id);
+        while (true) {
+            if (objects[index] == null) {
+               return false;
+            }
+            if (keys[index] == id) {
+                return true;
+            }
+            index++;
+            if (index == keys.length) {
+                index = 0;
+            }
+        }
+    }
+
+    public void expand(int size) {
+        int l = 4 * size / 3;
+        if (l <= keys.length) {
+            return;
+        }
+        int n = tableSizeFor(l);
+        LongMap<T> temp = new LongMap<>(bitCount);
+        temp.initialize(n);
+        // Optimization, avoid growing while copying bits
+        if (bitCount > 0 && !bitSet.isEmpty()) {
+           temp.claimBits();
+           claimBits();
+        }
+        for (int tIndex = 0; tIndex < keys.length; tIndex++) {
+            T o = objects[tIndex];
+            if (o != null) {
+                long key = keys[tIndex];
+                temp.put(key, o);
+                if (bitCount != 0) {
+                    for (int bIndex = 0; bIndex < bitCount; bIndex++) {
+                        boolean bitValue = isSetId(key, bIndex);
+                        if (bitValue) {
+                            temp.setId(key, bIndex);
+                        }
+                    }
+                }
+            }
+        }
+        keys = temp.keys;
+        objects = temp.objects;
+        shift = temp.shift;
+        bitSet = temp.bitSet;
+    }
+
+    public void put(long id, T object) {
+        if (keys == EMPTY_KEYS) {
+            // Lazy initialization
+            initialize(DEFAULT_SIZE);
+        }
+        if (object == null) {
+            object = (T) NULL_OBJECT;
+        }
+
+        int index = index(id);
+        // probe for empty slot
+        while (true) {
+            if (objects[index] == null) {
+                keys[index] = id;
+                objects[index] = object;
+                count++;
+                // Don't expand lazy since it
+                // can cause resize when replacing
+                // an object.
+                if (count > 3 * keys.length / 4) {
+                    expand(2 * keys.length);
+                }
+                return;
+            }
+            // if it already exists, replace
+            if (keys[index] == id) {
+                objects[index] = object;
+                return;
+            }
+            index++;
+            if (index == keys.length) {
+                index = 0;
+            }
+        }
+    }
+    public T getAt(int tableIndex) {
+        T o =  objects[tableIndex];
+        return o == NULL_OBJECT ? null : o;
+    }
+
+    public T get(long id) {
+        if (keys == EMPTY_KEYS) {
+            return null;
+        }
+        int index = index(id);
+        while (true) {
+            if (objects[index] == null) {
+                return null;
+            }
+            if (keys[index] == id) {
+                return getAt(index);
+            }
+            index++;
+            if (index == keys.length) {
+                index = 0;
+            }
+        }
+    }
+
+    private int index(long id) {
+        return (int) ((id * -7046029254386353131L) >>> shift);
+    }
+
+    // Copied from HashMap::tableSizeFor
+    private static final int tableSizeFor(int cap) {
+        int n = -1 >>> Integer.numberOfLeadingZeros(cap - 1);
+        return (n < 0) ? 1 : (n >= MAXIMUM_CAPACITY) ? MAXIMUM_CAPACITY : n + 1;
+    }
+
+    public void forEachKey(LongConsumer keyTraverser) {
+        for (int i = 0; i < keys.length; i++) {
+            if (objects[i] != null) {
+                keyTraverser.accept(keys[i]);
+            }
+        }
+    }
+
+    public void forEach(Consumer<T> consumer) {
+        for (int i = 0; i < keys.length; i++) {
+            T o = objects[i];
+            if (o != null) {
+                consumer.accept(o);
+            }
+        }
+    }
+
+    public int size() {
+        return count;
+    }
+
+    public String toString() {
+        StringBuilder sb = new StringBuilder();
+        for (int i = 0; i < objects.length; i++) {
+            sb.append(i);
+            sb.append(": id=");
+            sb.append(keys[i]);
+            sb.append(" ");
+            sb.append(objects[i]);
+            sb.append("\n");
+        }
+        return sb.toString();
+    }
+}