jdk/test/java/util/Map/InPlaceOpsCollisions.java
changeset 17939 bd750ec19d82
parent 13817 23f16430801a
child 19806 dda89341ee2d
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/jdk/test/java/util/Map/InPlaceOpsCollisions.java	Tue Jun 04 10:04:28 2013 +0100
@@ -0,0 +1,665 @@
+/*
+ * Copyright (c) 2013, 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.
+ */
+
+/*
+ * @test
+ * @bug 8005698
+ * @run main InPlaceOpsCollisions -shortrun
+ * @run main/othervm -Djdk.map.randomseed=true InPlaceOpsCollisions -shortrun
+ * @summary Ensure overrides of in-place operations in Maps behave well with lots of collisions.
+ * @author Brent Christian
+ */
+import java.util.*;
+import java.util.function.*;
+
+public class InPlaceOpsCollisions {
+
+    /**
+     * Number of elements per map.
+     */
+    private static final int TEST_SIZE = 5000;
+
+    final static class HashableInteger implements Comparable<HashableInteger> {
+
+        final int value;
+        final int hashmask; //yes duplication
+
+        HashableInteger(int value, int hashmask) {
+            this.value = value;
+            this.hashmask = hashmask;
+        }
+
+        @Override
+        public boolean equals(Object obj) {
+            if (obj instanceof HashableInteger) {
+                HashableInteger other = (HashableInteger) obj;
+
+                return other.value == value;
+            }
+
+            return false;
+        }
+
+        @Override
+        public int hashCode() {
+            return value % hashmask;
+        }
+
+        @Override
+        public int compareTo(HashableInteger o) {
+            return value - o.value;
+        }
+
+        @Override
+        public String toString() {
+            return Integer.toString(value);
+        }
+    }
+
+    static HashableInteger EXTRA_INT_VAL;
+    static String EXTRA_STRING_VAL;
+
+    private static Object[][] makeTestData(int size) {
+        HashableInteger UNIQUE_OBJECTS[] = new HashableInteger[size];
+        HashableInteger COLLIDING_OBJECTS[] = new HashableInteger[size];
+        String UNIQUE_STRINGS[] = new String[size];
+        String COLLIDING_STRINGS[] = new String[size];
+
+        for (int i = 0; i < size; i++) {
+            UNIQUE_OBJECTS[i] = new HashableInteger(i, Integer.MAX_VALUE);
+            COLLIDING_OBJECTS[i] = new HashableInteger(i, 10);
+            UNIQUE_STRINGS[i] = unhash(i);
+            COLLIDING_STRINGS[i] = (0 == i % 2)
+                    ? UNIQUE_STRINGS[i / 2]
+                    : "\u0000\u0000\u0000\u0000\u0000" + COLLIDING_STRINGS[i - 1];
+        }
+        EXTRA_INT_VAL = new HashableInteger(size, Integer.MAX_VALUE);
+        EXTRA_STRING_VAL = new String ("Extra Value");
+
+     return new Object[][] {
+            new Object[]{"Unique Objects", UNIQUE_OBJECTS},
+            new Object[]{"Colliding Objects", COLLIDING_OBJECTS},
+            new Object[]{"Unique Strings", UNIQUE_STRINGS},
+            new Object[]{"Colliding Strings", COLLIDING_STRINGS}
+        };
+    }
+
+    /**
+     * Returns a string with a hash equal to the argument.
+     *
+     * @return string with a hash equal to the argument.
+     */
+    public static String unhash(int target) {
+        StringBuilder answer = new StringBuilder();
+        if (target < 0) {
+            // String with hash of Integer.MIN_VALUE, 0x80000000
+            answer.append("\\u0915\\u0009\\u001e\\u000c\\u0002");
+
+            if (target == Integer.MIN_VALUE) {
+                return answer.toString();
+            }
+            // Find target without sign bit set
+            target = target & Integer.MAX_VALUE;
+        }
+
+        unhash0(answer, target);
+        return answer.toString();
+    }
+
+    private static void unhash0(StringBuilder partial, int target) {
+        int div = target / 31;
+        int rem = target % 31;
+
+        if (div <= Character.MAX_VALUE) {
+            if (div != 0) {
+                partial.append((char) div);
+            }
+            partial.append((char) rem);
+        } else {
+            unhash0(partial, div);
+            partial.append((char) rem);
+        }
+    }
+
+    private static void realMain(String[] args) throws Throwable {
+        boolean shortRun = args.length > 0 && args[0].equals("-shortrun");
+
+        Object[][] mapKeys = makeTestData(shortRun ? (TEST_SIZE / 2) : TEST_SIZE);
+
+        // loop through data sets
+        for (Object[] keys_desc : mapKeys) {
+            Map<Object, Object>[] maps = (Map<Object, Object>[]) new Map[]{
+                        new HashMap<>(),
+                        new LinkedHashMap<>(),
+                    };
+
+            // for each map type.
+            for (Map<Object, Object> map : maps) {
+                String desc = (String) keys_desc[0];
+                Object[] keys = (Object[]) keys_desc[1];
+                try {
+                    testInPlaceOps(map, desc, keys);
+                } catch(Exception all) {
+                    unexpected("Failed for " + map.getClass().getName() + " with " + desc, all);
+                }
+            }
+        }
+    }
+
+    private static <T> void testInsertion(Map<T, T> map, String keys_desc, T[] keys) {
+        check("map empty", (map.size() == 0) && map.isEmpty());
+
+        for (int i = 0; i < keys.length; i++) {
+            check(String.format("insertion: map expected size m%d != i%d", map.size(), i),
+                    map.size() == i);
+            check(String.format("insertion: put(%s[%d])", keys_desc, i), null == map.put(keys[i], keys[i]));
+            check(String.format("insertion: containsKey(%s[%d])", keys_desc, i), map.containsKey(keys[i]));
+            check(String.format("insertion: containsValue(%s[%d])", keys_desc, i), map.containsValue(keys[i]));
+        }
+
+        check(String.format("map expected size m%d != k%d", map.size(), keys.length),
+                map.size() == keys.length);
+    }
+
+
+    private static <T> void testInPlaceOps(Map<T, T> map, String keys_desc, T[] keys) {
+        System.out.println(map.getClass() + " : " + keys_desc + ", testInPlaceOps");
+        System.out.flush();
+
+        testInsertion(map, keys_desc, keys);
+        testPutIfAbsent(map, keys_desc, keys);
+
+        map.clear();
+        testInsertion(map, keys_desc, keys);
+        testRemoveMapping(map, keys_desc, keys);
+
+        map.clear();
+        testInsertion(map, keys_desc, keys);
+        testReplaceOldValue(map, keys_desc, keys);
+
+        map.clear();
+        testInsertion(map, keys_desc, keys);
+        testReplaceIfMapped(map, keys_desc, keys);
+
+        map.clear();
+        testInsertion(map, keys_desc, keys);
+        testComputeIfAbsent(map, keys_desc, keys, (k) -> getExtraVal(keys[0]));
+
+        map.clear();
+        testInsertion(map, keys_desc, keys);
+        testComputeIfAbsent(map, keys_desc, keys, (k) -> null);
+
+        map.clear();
+        testInsertion(map, keys_desc, keys);
+        testComputeIfPresent(map, keys_desc, keys, (k, v) -> getExtraVal(keys[0]));
+
+        map.clear();
+        testInsertion(map, keys_desc, keys);
+        testComputeIfPresent(map, keys_desc, keys, (k, v) -> null);
+
+        if (!keys_desc.contains("Strings")) { // avoid parseInt() number format error
+            map.clear();
+            testInsertion(map, keys_desc, keys);
+            testComputeNonNull(map, keys_desc, keys);
+        }
+
+        map.clear();
+        testInsertion(map, keys_desc, keys);
+        testComputeNull(map, keys_desc, keys);
+
+        if (!keys_desc.contains("Strings")) { // avoid parseInt() number format error
+            map.clear();
+            testInsertion(map, keys_desc, keys);
+            testMergeNonNull(map, keys_desc, keys);
+        }
+
+        map.clear();
+        testInsertion(map, keys_desc, keys);
+        testMergeNull(map, keys_desc, keys);
+    }
+
+
+
+    private static <T> void testPutIfAbsent(Map<T, T> map, String keys_desc, T[] keys) {
+        T extraVal = getExtraVal(keys[0]);
+        T retVal;
+        removeOddKeys(map, keys);
+        for (int i = 0; i < keys.length; i++) {
+            retVal = map.putIfAbsent(keys[i], extraVal);
+            if (i % 2 == 0) { // even: not absent, not put
+                check(String.format("putIfAbsent: (%s[%d]) retVal", keys_desc, i), retVal == keys[i]);
+                check(String.format("putIfAbsent: get(%s[%d])", keys_desc, i), keys[i] == map.get(keys[i]));
+                check(String.format("putIfAbsent: containsValue(%s[%d])", keys_desc, i), map.containsValue(keys[i]));
+            } else { // odd: absent, was put
+                check(String.format("putIfAbsent: (%s[%d]) retVal", keys_desc, i), retVal == null);
+                check(String.format("putIfAbsent: get(%s[%d])", keys_desc, i), extraVal == map.get(keys[i]));
+                check(String.format("putIfAbsent: !containsValue(%s[%d])", keys_desc, i), !map.containsValue(keys[i]));
+            }
+            check(String.format("insertion: containsKey(%s[%d])", keys_desc, i), map.containsKey(keys[i]));
+        }
+        check(String.format("map expected size m%d != k%d", map.size(), keys.length),
+                map.size() == keys.length);
+    }
+
+    private static <T> void testRemoveMapping(Map<T, T> map, String keys_desc, T[] keys) {
+        T extraVal = getExtraVal(keys[0]);
+        boolean removed;
+        int removes = 0;
+        remapOddKeys(map, keys);
+        for (int i = 0; i < keys.length; i++) {
+            removed = map.remove(keys[i], keys[i]);
+            if (i % 2 == 0) { // even: original mapping, should be removed
+                check(String.format("removeMapping: retVal(%s[%d])", keys_desc, i), removed);
+                check(String.format("removeMapping: get(%s[%d])", keys_desc, i), null == map.get(keys[i]));
+                check(String.format("removeMapping: !containsKey(%s[%d])", keys_desc, i), !map.containsKey(keys[i]));
+                check(String.format("removeMapping: !containsValue(%s[%d])", keys_desc, i), !map.containsValue(keys[i]));
+                removes++;
+            } else { // odd: new mapping, not removed
+                check(String.format("removeMapping: retVal(%s[%d])", keys_desc, i), !removed);
+                check(String.format("removeMapping: get(%s[%d])", keys_desc, i), extraVal == map.get(keys[i]));
+                check(String.format("removeMapping: containsKey(%s[%d])", keys_desc, i), map.containsKey(keys[i]));
+                check(String.format("removeMapping: containsValue(%s[%d])", keys_desc, i), map.containsValue(extraVal));
+            }
+        }
+        check(String.format("map expected size m%d != k%d", map.size(), keys.length - removes),
+                map.size() == keys.length - removes);
+    }
+
+    private static <T> void testReplaceOldValue(Map<T, T> map, String keys_desc, T[] keys) {
+        // remap odds to extraVal
+        // call replace to replace for extraVal, for all keys
+        // check that all keys map to value from keys array
+        T extraVal = getExtraVal(keys[0]);
+        boolean replaced;
+        remapOddKeys(map, keys);
+
+        for (int i = 0; i < keys.length; i++) {
+            replaced = map.replace(keys[i], extraVal, keys[i]);
+            if (i % 2 == 0) { // even: original mapping, should not be replaced
+                check(String.format("replaceOldValue: retVal(%s[%d])", keys_desc, i), !replaced);
+            } else { // odd: new mapping, should be replaced
+                check(String.format("replaceOldValue: get(%s[%d])", keys_desc, i), replaced);
+            }
+            check(String.format("replaceOldValue: get(%s[%d])", keys_desc, i), keys[i] == map.get(keys[i]));
+            check(String.format("replaceOldValue: containsKey(%s[%d])", keys_desc, i), map.containsKey(keys[i]));
+            check(String.format("replaceOldValue: containsValue(%s[%d])", keys_desc, i), map.containsValue(keys[i]));
+//            removes++;
+        }
+        check(String.format("replaceOldValue: !containsValue(%s[%s])", keys_desc, extraVal.toString()), !map.containsValue(extraVal));
+        check(String.format("map expected size m%d != k%d", map.size(), keys.length),
+                map.size() == keys.length);
+    }
+
+    // TODO: Test case for key mapped to null value
+    private static <T> void testReplaceIfMapped(Map<T, T> map, String keys_desc, T[] keys) {
+        // remove odd keys
+        // call replace for all keys[]
+        // odd keys should remain absent, even keys should be mapped to EXTRA, no value from keys[] should be in map
+        T extraVal = getExtraVal(keys[0]);
+        int expectedSize1 = 0;
+        removeOddKeys(map, keys);
+        int expectedSize2 = map.size();
+
+        for (int i = 0; i < keys.length; i++) {
+            T retVal = map.replace(keys[i], extraVal);
+            if (i % 2 == 0) { // even: still in map, should be replaced
+                check(String.format("replaceIfMapped: retVal(%s[%d])", keys_desc, i), retVal == keys[i]);
+                check(String.format("replaceIfMapped: get(%s[%d])", keys_desc, i), extraVal == map.get(keys[i]));
+                check(String.format("replaceIfMapped: containsKey(%s[%d])", keys_desc, i), map.containsKey(keys[i]));
+                expectedSize1++;
+            } else { // odd: was removed, should not be replaced
+                check(String.format("replaceIfMapped: retVal(%s[%d])", keys_desc, i), retVal == null);
+                check(String.format("replaceIfMapped: get(%s[%d])", keys_desc, i), null == map.get(keys[i]));
+                check(String.format("replaceIfMapped: containsKey(%s[%d])", keys_desc, i), !map.containsKey(keys[i]));
+            }
+            check(String.format("replaceIfMapped: !containsValue(%s[%d])", keys_desc, i), !map.containsValue(keys[i]));
+        }
+        check(String.format("replaceIfMapped: containsValue(%s[%s])", keys_desc, extraVal.toString()), map.containsValue(extraVal));
+        check(String.format("map expected size#1 m%d != k%d", map.size(), expectedSize1),
+                map.size() == expectedSize1);
+        check(String.format("map expected size#2 m%d != k%d", map.size(), expectedSize2),
+                map.size() == expectedSize2);
+
+    }
+
+    private static <T> void testComputeIfAbsent(Map<T, T> map, String keys_desc, T[] keys,
+                                                Function<T,T> mappingFunction) {
+        // remove a third of the keys
+        // call computeIfAbsent for all keys, func returns EXTRA
+        // check that removed keys now -> EXTRA, other keys -> original val
+        T expectedVal = mappingFunction.apply(keys[0]);
+        T retVal;
+        int expectedSize = 0;
+        removeThirdKeys(map, keys);
+        for (int i = 0; i < keys.length; i++) {
+            retVal = map.computeIfAbsent(keys[i], mappingFunction);
+            if (i % 3 != 2) { // key present, not computed
+                check(String.format("computeIfAbsent: (%s[%d]) retVal", keys_desc, i), retVal == keys[i]);
+                check(String.format("computeIfAbsent: get(%s[%d])", keys_desc, i), keys[i] == map.get(keys[i]));
+                check(String.format("computeIfAbsent: containsValue(%s[%d])", keys_desc, i), map.containsValue(keys[i]));
+                check(String.format("insertion: containsKey(%s[%d])", keys_desc, i), map.containsKey(keys[i]));
+                expectedSize++;
+            } else { // key absent, computed unless function return null
+                check(String.format("computeIfAbsent: (%s[%d]) retVal", keys_desc, i), retVal == expectedVal);
+                check(String.format("computeIfAbsent: get(%s[%d])", keys_desc, i), expectedVal == map.get(keys[i]));
+                check(String.format("computeIfAbsent: !containsValue(%s[%d])", keys_desc, i), !map.containsValue(keys[i]));
+                // mapping should not be added if function returns null
+                check(String.format("insertion: containsKey(%s[%d])", keys_desc, i), map.containsKey(keys[i]) != (expectedVal == null));
+                if (expectedVal != null) { expectedSize++; }
+            }
+        }
+        if (expectedVal != null) {
+            check(String.format("computeIfAbsent: containsValue(%s[%s])", keys_desc, expectedVal), map.containsValue(expectedVal));
+        }
+        check(String.format("map expected size m%d != k%d", map.size(), expectedSize),
+                map.size() == expectedSize);
+    }
+
+    private static <T> void testComputeIfPresent(Map<T, T> map, String keys_desc, T[] keys,
+                                                BiFunction<T,T,T> mappingFunction) {
+        // remove a third of the keys
+        // call testComputeIfPresent for all keys[]
+        // removed keys should remain absent, even keys should be mapped to $RESULT
+        // no value from keys[] should be in map
+        T funcResult = mappingFunction.apply(keys[0], keys[0]);
+        int expectedSize1 = 0;
+        removeThirdKeys(map, keys);
+
+        for (int i = 0; i < keys.length; i++) {
+            T retVal = map.computeIfPresent(keys[i], mappingFunction);
+            if (i % 3 != 2) { // key present
+                if (funcResult == null) { // was removed
+                    check(String.format("replaceIfMapped: containsKey(%s[%d])", keys_desc, i), !map.containsKey(keys[i]));
+                } else { // value was replaced
+                    check(String.format("replaceIfMapped: containsKey(%s[%d])", keys_desc, i), map.containsKey(keys[i]));
+                    expectedSize1++;
+                }
+                check(String.format("computeIfPresent: retVal(%s[%s])", keys_desc, i), retVal == funcResult);
+                check(String.format("replaceIfMapped: get(%s[%d])", keys_desc, i), funcResult == map.get(keys[i]));
+
+            } else { // odd: was removed, should not be replaced
+                check(String.format("replaceIfMapped: retVal(%s[%d])", keys_desc, i), retVal == null);
+                check(String.format("replaceIfMapped: get(%s[%d])", keys_desc, i), null == map.get(keys[i]));
+                check(String.format("replaceIfMapped: containsKey(%s[%d])", keys_desc, i), !map.containsKey(keys[i]));
+            }
+            check(String.format("replaceIfMapped: !containsValue(%s[%d])", keys_desc, i), !map.containsValue(keys[i]));
+        }
+        check(String.format("map expected size#1 m%d != k%d", map.size(), expectedSize1),
+                map.size() == expectedSize1);
+    }
+
+    private static <T> void testComputeNonNull(Map<T, T> map, String keys_desc, T[] keys) {
+        // remove a third of the keys
+        // call compute() for all keys[]
+        // all keys should be present: removed keys -> EXTRA, others to k-1
+        BiFunction<T,T,T> mappingFunction = (k, v) -> {
+                if (v == null) {
+                    return getExtraVal(keys[0]);
+                } else {
+                    return keys[Integer.parseInt(k.toString()) - 1];
+                }
+            };
+        T extraVal = getExtraVal(keys[0]);
+        removeThirdKeys(map, keys);
+        for (int i = 1; i < keys.length; i++) {
+            T retVal = map.compute(keys[i], mappingFunction);
+            if (i % 3 != 2) { // key present, should be mapped to k-1
+                check(String.format("compute: retVal(%s[%d])", keys_desc, i), retVal == keys[i-1]);
+                check(String.format("compute: get(%s[%d])", keys_desc, i), keys[i-1] == map.get(keys[i]));
+            } else { // odd: was removed, should be replaced with EXTRA
+                check(String.format("compute: retVal(%s[%d])", keys_desc, i), retVal == extraVal);
+                check(String.format("compute: get(%s[%d])", keys_desc, i), extraVal == map.get(keys[i]));
+            }
+            check(String.format("compute: containsKey(%s[%d])", keys_desc, i), map.containsKey(keys[i]));
+        }
+        check(String.format("map expected size#1 m%d != k%d", map.size(), keys.length),
+                map.size() == keys.length);
+        check(String.format("compute: containsValue(%s[%s])", keys_desc, extraVal.toString()), map.containsValue(extraVal));
+        check(String.format("compute: !containsValue(%s,[null])", keys_desc), !map.containsValue(null));
+    }
+
+    private static <T> void testComputeNull(Map<T, T> map, String keys_desc, T[] keys) {
+        // remove a third of the keys
+        // call compute() for all keys[]
+        // removed keys should -> EXTRA
+        // for other keys: func returns null, should have no mapping
+        BiFunction<T,T,T> mappingFunction = (k, v) -> {
+            // if absent/null -> EXTRA
+            // if present -> null
+            if (v == null) {
+                return getExtraVal(keys[0]);
+            } else {
+                return null;
+            }
+        };
+        T extraVal = getExtraVal(keys[0]);
+        int expectedSize = 0;
+        removeThirdKeys(map, keys);
+        for (int i = 0; i < keys.length; i++) {
+            T retVal = map.compute(keys[i], mappingFunction);
+            if (i % 3 != 2) { // key present, func returned null, should be absent from map
+                check(String.format("compute: retVal(%s[%d])", keys_desc, i), retVal == null);
+                check(String.format("compute: get(%s[%d])", keys_desc, i), null == map.get(keys[i]));
+                check(String.format("compute: containsKey(%s[%d])", keys_desc, i), !map.containsKey(keys[i]));
+                check(String.format("compute: containsValue(%s[%s])", keys_desc, i), !map.containsValue(keys[i]));
+            } else { // odd: was removed, should now be mapped to EXTRA
+                check(String.format("compute: retVal(%s[%d])", keys_desc, i), retVal == extraVal);
+                check(String.format("compute: get(%s[%d])", keys_desc, i), extraVal == map.get(keys[i]));
+                check(String.format("compute: containsKey(%s[%d])", keys_desc, i), map.containsKey(keys[i]));
+                expectedSize++;
+            }
+        }
+        check(String.format("compute: containsValue(%s[%s])", keys_desc, extraVal.toString()), map.containsValue(extraVal));
+        check(String.format("map expected size#1 m%d != k%d", map.size(), expectedSize),
+                map.size() == expectedSize);
+    }
+
+    private static <T> void testMergeNonNull(Map<T, T> map, String keys_desc, T[] keys) {
+        // remove a third of the keys
+        // call merge() for all keys[]
+        // all keys should be present: removed keys now -> EXTRA, other keys -> k-1
+
+        // Map to preceding key
+        BiFunction<T,T,T> mappingFunction = (k, v) -> keys[Integer.parseInt(k.toString()) - 1];
+        T extraVal = getExtraVal(keys[0]);
+        removeThirdKeys(map, keys);
+        for (int i = 1; i < keys.length; i++) {
+            T retVal = map.merge(keys[i], extraVal, mappingFunction);
+            if (i % 3 != 2) { // key present, should be mapped to k-1
+                check(String.format("compute: retVal(%s[%d])", keys_desc, i), retVal == keys[i-1]);
+                check(String.format("compute: get(%s[%d])", keys_desc, i), keys[i-1] == map.get(keys[i]));
+            } else { // odd: was removed, should be replaced with EXTRA
+                check(String.format("compute: retVal(%s[%d])", keys_desc, i), retVal == extraVal);
+                check(String.format("compute: get(%s[%d])", keys_desc, i), extraVal == map.get(keys[i]));
+            }
+            check(String.format("compute: containsKey(%s[%d])", keys_desc, i), map.containsKey(keys[i]));
+        }
+
+        check(String.format("map expected size#1 m%d != k%d", map.size(), keys.length),
+                map.size() == keys.length);
+        check(String.format("compute: containsValue(%s[%s])", keys_desc, extraVal.toString()), map.containsValue(extraVal));
+        check(String.format("compute: !containsValue(%s,[null])", keys_desc), !map.containsValue(null));
+
+    }
+
+    private static <T> void testMergeNull(Map<T, T> map, String keys_desc, T[] keys) {
+        // remove a third of the keys
+        // call merge() for all keys[]
+        // result: removed keys -> EXTRA, other keys absent
+
+        BiFunction<T,T,T> mappingFunction = (k, v) -> null;
+        T extraVal = getExtraVal(keys[0]);
+        int expectedSize = 0;
+        removeThirdKeys(map, keys);
+        for (int i = 0; i < keys.length; i++) {
+            T retVal = map.merge(keys[i], extraVal, mappingFunction);
+            if (i % 3 != 2) { // key present, func returned null, should be absent from map
+                check(String.format("compute: retVal(%s[%d])", keys_desc, i), retVal == null);
+                check(String.format("compute: get(%s[%d])", keys_desc, i), null == map.get(keys[i]));
+                check(String.format("compute: containsKey(%s[%d])", keys_desc, i), !map.containsKey(keys[i]));
+            } else { // odd: was removed, should now be mapped to EXTRA
+                check(String.format("compute: retVal(%s[%d])", keys_desc, i), retVal == extraVal);
+                check(String.format("compute: get(%s[%d])", keys_desc, i), extraVal == map.get(keys[i]));
+                check(String.format("compute: containsKey(%s[%d])", keys_desc, i), map.containsKey(keys[i]));
+                expectedSize++;
+            }
+            check(String.format("compute: containsValue(%s[%s])", keys_desc, i), !map.containsValue(keys[i]));
+        }
+        check(String.format("compute: containsValue(%s[%s])", keys_desc, extraVal.toString()), map.containsValue(extraVal));
+        check(String.format("map expected size#1 m%d != k%d", map.size(), expectedSize),
+                map.size() == expectedSize);
+    }
+
+    /*
+     * Return the EXTRA val for the key type being used
+     */
+    private static <T> T getExtraVal(T key) {
+        if (key instanceof HashableInteger) {
+            return (T)EXTRA_INT_VAL;
+        } else {
+            return (T)EXTRA_STRING_VAL;
+        }
+    }
+
+    /*
+     * Remove half of the keys
+     */
+    private static <T> void removeOddKeys(Map<T, T> map, /*String keys_desc, */ T[] keys) {
+        int removes = 0;
+        for (int i = 0; i < keys.length; i++) {
+            if (i % 2 != 0) {
+                map.remove(keys[i]);
+                removes++;
+            }
+        }
+        check(String.format("map expected size m%d != k%d", map.size(), keys.length - removes),
+                map.size() == keys.length - removes);
+    }
+
+    /*
+     * Remove every third key
+     * This will hopefully leave some removed keys in TreeBins for, e.g., computeIfAbsent
+     * w/ a func that returns null.
+     *
+     * TODO: consider using this in other tests (and maybe adding a remapThirdKeys)
+     */
+    private static <T> void removeThirdKeys(Map<T, T> map, /*String keys_desc, */ T[] keys) {
+        int removes = 0;
+        for (int i = 0; i < keys.length; i++) {
+            if (i % 3 == 2) {
+                map.remove(keys[i]);
+                removes++;
+            }
+        }
+        check(String.format("map expected size m%d != k%d", map.size(), keys.length - removes),
+                map.size() == keys.length - removes);
+    }
+
+    /*
+     * Re-map the odd-numbered keys to map to the EXTRA value
+     */
+    private static <T> void remapOddKeys(Map<T, T> map, /*String keys_desc, */ T[] keys) {
+        T extraVal = getExtraVal(keys[0]);
+        for (int i = 0; i < keys.length; i++) {
+            if (i % 2 != 0) {
+                map.put(keys[i], extraVal);
+            }
+        }
+    }
+
+    //--------------------- Infrastructure ---------------------------
+    static volatile int passed = 0, failed = 0;
+
+    static void pass() {
+        passed++;
+    }
+
+    static void fail() {
+        failed++;
+        (new Error("Failure")).printStackTrace(System.err);
+    }
+
+    static void fail(String msg) {
+        failed++;
+        (new Error("Failure: " + msg)).printStackTrace(System.err);
+    }
+
+    static void abort() {
+        fail();
+        System.exit(1);
+    }
+
+    static void abort(String msg) {
+        fail(msg);
+        System.exit(1);
+    }
+
+    static void unexpected(String msg, Throwable t) {
+        System.err.println("Unexpected: " + msg);
+        unexpected(t);
+    }
+
+    static void unexpected(Throwable t) {
+        failed++;
+        t.printStackTrace(System.err);
+    }
+
+    static void check(boolean cond) {
+        if (cond) {
+            pass();
+        } else {
+            fail();
+        }
+    }
+
+    static void check(String desc, boolean cond) {
+        if (cond) {
+            pass();
+        } else {
+            fail(desc);
+        }
+    }
+
+    static void equal(Object x, Object y) {
+        if (Objects.equals(x, y)) {
+            pass();
+        } else {
+            fail(x + " not equal to " + y);
+        }
+    }
+
+    public static void main(String[] args) throws Throwable {
+        Thread.currentThread().setName(Collisions.class.getName());
+//        Thread.currentThread().setPriority(Thread.MAX_PRIORITY);
+        try {
+            realMain(args);
+        } catch (Throwable t) {
+            unexpected(t);
+        }
+
+        System.out.printf("%nPassed = %d, failed = %d%n%n", passed, failed);
+        if (failed > 0) {
+            throw new Error("Some tests failed");
+        }
+    }
+}