Added 2 missing lockfree types

src/dorkbox/util/collections/LockFreeArrayList.java

@@ -0,0 +1,109 @@
+/*
+ * Copyright 2018 dorkbox, llc
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package dorkbox.util.collections;
+
+import java.util.ArrayList;
+import java.util.Collection;
+import java.util.concurrent.atomic.AtomicReferenceFieldUpdater;
+
+/**
+ * This class uses the "single-writer-principle" for lock-free publication.
+ *
+ * Since there are only 2 methods to guarantee that modifications can only be called one-at-a-time (either it is only called by
+ * one thread, or only one thread can access it at a time) -- we chose the 2nd option -- and use 'synchronized' to make sure that only
+ * one thread can access this modification methods at a time. Getting or checking the presence of values can then happen in a lock-free
+ * manner.
+ *
+ * According to my benchmarks, this is approximately 25% faster than ConcurrentHashMap for (all types of) reads, and a lot slower for
+ * contended writes.
+ *
+ * This data structure is for many-read/few-write scenarios
+ */
+public final
+class LockFreeArrayList<E> {
+    // Recommended for best performance while adhering to the "single writer principle". Must be static-final
+    private static final AtomicReferenceFieldUpdater<LockFreeArrayList, ArrayList> listRef =
+            AtomicReferenceFieldUpdater.newUpdater(LockFreeArrayList.class,
+                                                   ArrayList.class, "arrayList");
+    private volatile ArrayList<E> arrayList = new ArrayList<>();
+
+
+    public
+    LockFreeArrayList(){}
+
+
+    public
+    LockFreeArrayList(Collection<E> elements) {
+        arrayList.addAll(elements);
+    }
+
+    // synchronized is used here to ensure the "single writer principle", and make sure that ONLY one thread at a time can enter this
+    // section. Because of this, we can have unlimited reader threads all going at the same time, without contention (which is our
+    // use-case 99% of the time)
+    public synchronized
+    void clear() {
+        arrayList.clear();
+    }
+
+    // synchronized is used here to ensure the "single writer principle", and make sure that ONLY one thread at a time can enter this
+    // section. Because of this, we can have unlimited reader threads all going at the same time, without contention (which is our
+    // use-case 99% of the time)
+    public synchronized
+    boolean add(final E element) {
+        return arrayList.add(element);
+    }
+
+    // synchronized is used here to ensure the "single writer principle", and make sure that ONLY one thread at a time can enter this
+    // section. Because of this, we can have unlimited reader threads all going at the same time, without contention (which is our
+    // use-case 99% of the time)
+    public synchronized
+    void addAll(final Collection<E> elements) {
+        arrayList.addAll(elements);
+    }
+
+    public synchronized
+    E get(int index) {
+        return arrayList.get(index);
+    }
+
+    // synchronized is used here to ensure the "single writer principle", and make sure that ONLY one thread at a time can enter this
+    // section. Because of this, we can have unlimited reader threads all going at the same time, without contention (which is our
+    // use-case 99% of the time)
+    public synchronized
+    boolean remove(final E element) {
+        return arrayList.remove(element);
+    }
+
+    public
+    int size() {
+        return listRef.get(this).size();
+    }
+
+    // lock-free get
+    public
+    boolean contains(final E element) {
+        // use the SWP to get the value
+        return listRef.get(this).contains(element);
+    }
+
+    // lock-free get
+    @SuppressWarnings("unchecked")
+    public
+    ArrayList<E> elements() {
+        // use the SWP to get the value
+        return listRef.get(this);
+    }
+}

src/dorkbox/util/collections/LockFreeHashSet.java

@@ -0,0 +1,106 @@
+/*
+ * Copyright 2018 dorkbox, llc
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package dorkbox.util.collections;
+
+import java.util.Collection;
+import java.util.HashSet;
+import java.util.Set;
+import java.util.concurrent.atomic.AtomicReferenceFieldUpdater;
+
+/**
+ * This class uses the "single-writer-principle" for lock-free publication.
+ *
+ * Since there are only 2 methods to guarantee that modifications can only be called one-at-a-time (either it is only called by
+ * one thread, or only one thread can access it at a time) -- we chose the 2nd option -- and use 'synchronized' to make sure that only
+ * one thread can access this modification methods at a time. Getting or checking the presence of values can then happen in a lock-free
+ * manner.
+ *
+ * According to my benchmarks, this is approximately 25% faster than ConcurrentHashMap for (all types of) reads, and a lot slower for
+ * contended writes.
+ *
+ * This data structure is for many-read/few-write scenarios
+ */
+public final
+class LockFreeHashSet<E> {
+    // Recommended for best performance while adhering to the "single writer principle". Must be static-final
+    private static final AtomicReferenceFieldUpdater<LockFreeHashSet, Set> setREF =
+            AtomicReferenceFieldUpdater.newUpdater(LockFreeHashSet.class,
+                                                   Set.class,
+                                                   "hashSet");
+    private volatile Set<E> hashSet = new HashSet<>();
+
+
+    public
+    LockFreeHashSet(){}
+
+
+    public
+    LockFreeHashSet(Collection<E> elements) {
+        hashSet.addAll(elements);
+    }
+
+    // synchronized is used here to ensure the "single writer principle", and make sure that ONLY one thread at a time can enter this
+    // section. Because of this, we can have unlimited reader threads all going at the same time, without contention (which is our
+    // use-case 99% of the time)
+    public synchronized
+    void clear() {
+        hashSet.clear();
+    }
+
+    // synchronized is used here to ensure the "single writer principle", and make sure that ONLY one thread at a time can enter this
+    // section. Because of this, we can have unlimited reader threads all going at the same time, without contention (which is our
+    // use-case 99% of the time)
+    public synchronized
+    boolean add(final E element) {
+        return hashSet.add(element);
+    }
+
+    // synchronized is used here to ensure the "single writer principle", and make sure that ONLY one thread at a time can enter this
+    // section. Because of this, we can have unlimited reader threads all going at the same time, without contention (which is our
+    // use-case 99% of the time)
+    public synchronized
+    void addAll(final Collection<E> elements) {
+        hashSet.addAll(elements);
+    }
+
+    // synchronized is used here to ensure the "single writer principle", and make sure that ONLY one thread at a time can enter this
+    // section. Because of this, we can have unlimited reader threads all going at the same time, without contention (which is our
+    // use-case 99% of the time)
+    public synchronized
+    boolean remove(final E element) {
+        return hashSet.remove(element);
+    }
+
+    // lock-free get
+    public
+    boolean contains(final E element) {
+        // use the SWP to get the value
+        return setREF.get(this).contains(element);
+    }
+
+    // lock-free get
+    @SuppressWarnings("unchecked")
+    public
+    Set<E> elements() {
+        // use the SWP to get the value
+        return setREF.get(this);
+    }
+
+    public
+    int size() {
+        return setREF.get(this).size();
+    }
+}