OAK-11112 : added ensure capacity method to collectionutils to create…

… collections with expected capacity

oak-commons/src/main/java/org/apache/jackrabbit/oak/commons/collections/CollectionUtils.java

@@ -34,6 +34,8 @@
  */
 public class CollectionUtils {
 
+    private static final int MAX_CAPACITY = 1 << 30;
+
     private CollectionUtils() {
         // no instances for you
     }
@@ -131,12 +133,12 @@ public static <T> Set<T> toSet(@NotNull final T... elements) {
     public static <T> Iterable<T> toIterable(@NotNull final Iterator<T> iterator) {
         Objects.requireNonNull(iterator);
 
-        Iterable<T> delegate = new Iterable<T>() {
+        return new Iterable<>() {
 
             private boolean consumed = false;
 
             @Override
-            public Iterator<T> iterator() {
+            public @NotNull Iterator<T> iterator() {
                 if (consumed) {
                     throw new IllegalStateException("Iterator already returned once");
                 } else {
@@ -145,8 +147,6 @@ public Iterator<T> iterator() {
                 }
             }
         };
-
-        return delegate;
     }
 
     /**
@@ -170,7 +170,27 @@ public static <T> Stream<T> toStream(@NotNull Iterable<T> iterable) {
      *            iterator to convert
      * @return the stream (representing the remaining elements in the iterator)
      */
-    public static <T> Stream<T> toStream(Iterator<T> iterator) {
+    @NotNull
+    public static <T> Stream<T> toStream(@NotNull Iterator<T> iterator) {
         return StreamSupport.stream(toIterable(iterator).spliterator(), false);
     }
+
+    /**
+     * Ensure the capacity of a map or set given the expected number of elements.
+     *
+     * @param capacity the expected number of elements
+     * @return the capacity to use to avoid rehashing & collisions
+     */
+    public static int ensureCapacity(final int capacity) {
+
+        if (capacity < 0) {
+            throw new IllegalArgumentException("Capacity must be non-negative");
+        }
+
+        if (capacity > MAX_CAPACITY) {
+            return MAX_CAPACITY;
+        }
+
+        return 1 + (int) (capacity / 0.75f);
+    }
 }

oak-commons/src/test/java/org/apache/jackrabbit/oak/commons/collections/CollectionUtilsTest.java

@@ -30,6 +30,8 @@
 import java.util.stream.Collectors;
 import java.util.stream.Stream;
 
+import static org.junit.Assert.fail;
+
 public class CollectionUtilsTest {
 
     final List<String> data = Arrays.asList("one", "two", "three", null);
@@ -98,7 +100,7 @@ public void iteratorToIIteratable() {
         Assert.assertFalse(testit.hasNext());
         try {
             testit = iterable.iterator();
-            Assert.fail("should only work once");
+            fail("should only work once");
         } catch (IllegalStateException expected) {
             // that's what we want
         }
@@ -112,4 +114,22 @@ public void iteratorToStream() {
         List<String> result = stream.collect(Collectors.toList());
         Assert.assertEquals(input.toString(), result.toString());
     }
+
+    @Test
+    public void ensureCapacity() {
+        int capacity = CollectionUtils.ensureCapacity(8);
+        Assert.assertEquals(11, capacity);
+    }
+
+    @Test
+    public void ensureCapacityWithMaxValue() {
+        int capacity = CollectionUtils.ensureCapacity(1073741825);
+        Assert.assertEquals(1073741824, capacity);
+    }
+
+    @Test(expected = IllegalArgumentException.class)
+    public void ensureCapacityWithNegativeValue() {
+        int capacity = CollectionUtils.ensureCapacity(-8);
+        fail("Should throw IllegalArgumentException");
+    }
 }

oak-core/src/main/java/org/apache/jackrabbit/oak/security/user/GroupImpl.java

@@ -298,7 +298,7 @@ private Set<String> updateMembers(boolean isRemove, @NotNull String... memberIds
         }
 
         // calculate the contentID for each memberId and remember ids that cannot be processed
-        Map<String, String> updateMap = new HashMap<>((int)Math.ceil(memberIds.length / 0.75));
+        Map<String, String> updateMap = new HashMap<>(CollectionUtils.ensureCapacity(memberIds.length));
         MembershipProvider mp = getMembershipProvider();
         for (String memberId : memberIds) {
             if (Strings.isNullOrEmpty(memberId)) {

oak-core/src/main/java/org/apache/jackrabbit/oak/security/user/UserImporter.java

@@ -33,6 +33,7 @@
 import org.apache.jackrabbit.oak.api.Root;
 import org.apache.jackrabbit.oak.api.Tree;
 import org.apache.jackrabbit.oak.api.Type;
+import org.apache.jackrabbit.oak.commons.collections.CollectionUtils;
 import org.apache.jackrabbit.oak.namepath.NamePathMapper;
 import org.apache.jackrabbit.oak.plugins.identifier.IdentifierManager;
 import org.apache.jackrabbit.oak.plugins.memory.PropertyStates;
@@ -657,7 +658,7 @@ void process() throws RepositoryException {
         @NotNull
         Map<String, Authorizable> getAuthorizablesToAdd(@NotNull Group gr, @NotNull Map<String, Authorizable> toRemove,
                                                         @NotNull Map<String, String> nonExisting) throws RepositoryException {
-            Map<String, Authorizable> toAdd = new HashMap<>(members.size());
+            Map<String, Authorizable> toAdd = new HashMap<>(CollectionUtils.ensureCapacity(members.size()));
             for (String contentId : members) {
                 // NOTE: no need to check for re-mapped uuids with the referenceTracker because
                 // ImportUUIDBehavior.IMPORT_UUID_CREATE_NEW is not supported for user/group imports (see line 189)

oak-segment-tar/src/main/java/org/apache/jackrabbit/oak/segment/SegmentIdTable.java

@@ -30,6 +30,7 @@
 import java.util.Set;
 import java.util.UUID;
 
+import org.apache.jackrabbit.oak.commons.collections.CollectionUtils;
 import org.jetbrains.annotations.NotNull;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
@@ -130,7 +131,7 @@ void collectReferencedIds(Collection<SegmentId> ids) {
 
     private synchronized Collection<SegmentId> refresh() {
         int size = references.size();
-        Map<SegmentId, WeakReference<SegmentId>> ids = new HashMap<>((int)Math.ceil(size / 0.75));
+        Map<SegmentId, WeakReference<SegmentId>> ids = new HashMap<>(CollectionUtils.ensureCapacity(size));
 
         boolean hashCollisions = false;
         boolean emptyReferences = false;

oak-segment-tar/src/main/java/org/apache/jackrabbit/oak/segment/file/tar/GraphLoader.java

@@ -29,6 +29,7 @@
 import java.util.zip.CRC32;
 
 import org.apache.jackrabbit.oak.commons.Buffer;
+import org.apache.jackrabbit.oak.commons.collections.CollectionUtils;
 import org.apache.jackrabbit.oak.segment.util.ReaderAtEnd;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
@@ -93,7 +94,7 @@ public static Buffer loadGraph(ReaderAtEnd readerAtEnd) throws IOException {
     public static Map<UUID, List<UUID>> parseGraph(Buffer buffer) {
         int nEntries = buffer.getInt(buffer.limit() - 12);
 
-        Map<UUID, List<UUID>> graph = new HashMap<>((int)Math.ceil(nEntries / 0.75));
+        Map<UUID, List<UUID>> graph = new HashMap<>(CollectionUtils.ensureCapacity(nEntries));
 
         for (int i = 0; i < nEntries; i++) {
             long msb = buffer.getLong();