/*
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
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/*
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 *
 * Written by Doug Lea with assistance from members of JCP JSR-166
 * Expert Group and released to the public domain, as explained at
 * http://creativecommons.org/publicdomain/zero/1.0/
 */

package java.util.concurrent;

import java.util.AbstractSet;
import java.util.Collection;
import java.util.Iterator;
import java.util.Objects;
import java.util.Set;
import java.util.Spliterator;
import java.util.Spliterators;
import java.util.function.Consumer;
import java.util.function.Predicate;

/**
 * A {@link Set} that uses an internal {@link CopyOnWriteArrayList}
 * for all of its operations. Thus, it shares the same basic properties:
 * <ul>
 * <li>It is best suited for applications in which set sizes generally
 * stay small, read-only operations
 * vastly outnumber mutative operations, and you need
 * to prevent interference among threads during traversal.
 * <li>It is thread-safe.
 * <li>Mutative operations ({@code add}, {@code set}, {@code remove}, etc.)
 * are expensive since they usually entail copying the entire underlying
 * array.
 * <li>Iterators do not support the mutative {@code remove} operation.
 * <li>Traversal via iterators is fast and cannot encounter
 * interference from other threads. Iterators rely on
 * unchanging snapshots of the array at the time the iterators were
 * constructed.
 * </ul>
 *
 * <p><b>Sample Usage.</b> The following code sketch uses a
 * copy-on-write set to maintain a set of Handler objects that
 * perform some action upon state updates.
 *
 * <pre> {@code
 * class Handler { void handle(); ... }
 *
 * class X {
 * private final CopyOnWriteArraySet<Handler> handlers
 * = new CopyOnWriteArraySet<>();
 * public void addHandler(Handler h) { handlers.add(h); }
 *
 * private long internalState;
 * private synchronized void changeState() { internalState = ...; }
 *
 * public void update() {
 * changeState();
 * for (Handler handler : handlers)
 * handler.handle();
 * }
 * }}</pre>
 *
 * <p>This class is a member of the
 * <a href="{@docRoot}/java.base/java/util/package-summary.html#CollectionsFramework">
 * Java Collections Framework</a>.
 *
 * @see CopyOnWriteArrayList
 * @since 1.5
 * @author Doug Lea
 * @param <E> the type of elements held in this set
 */
public class CopyOnWriteArraySet<E> extends AbstractSet<E>
 implements java.io.Serializable {
 private static final long serialVersionUID = 5457747651344034263L;

 private final CopyOnWriteArrayList<E> al;

 /**
 * Creates an empty set.
 */
 public CopyOnWriteArraySet() {
 al = new CopyOnWriteArrayList<E>();
 }

 /**
 * Creates a set containing all of the elements of the specified
 * collection.
 *
 * @param c the collection of elements to initially contain
 * @throws NullPointerException if the specified collection is null
 */
 public CopyOnWriteArraySet(Collection<? extends E> c) {
 if (c.getClass() == CopyOnWriteArraySet.class) {
 @SuppressWarnings("unchecked") CopyOnWriteArraySet<E> cc =
 (CopyOnWriteArraySet<E>)c;
 al = new CopyOnWriteArrayList<E>(cc.al);
 }
 else {
 al = new CopyOnWriteArrayList<E>();
 al.addAllAbsent(c);
 }
 }

 /**
 * Returns the number of elements in this set.
 *
 * @return the number of elements in this set
 */
 public int size() {
 return al.size();
 }

 /**
 * Returns {@code true} if this set contains no elements.
 *
 * @return {@code true} if this set contains no elements
 */
 public boolean isEmpty() {
 return al.isEmpty();
 }

 /**
 * Returns {@code true} if this set contains the specified element.
 * More formally, returns {@code true} if and only if this set
 * contains an element {@code e} such that {@code Objects.equals(o, e)}.
 *
 * @param o element whose presence in this set is to be tested
 * @return {@code true} if this set contains the specified element
 */
 public boolean contains(Object o) {
 return al.contains(o);
 }

 /**
 * Returns an array containing all of the elements in this set.
 * If this set makes any guarantees as to what order its elements
 * are returned by its iterator, this method must return the
 * elements in the same order.
 *
 * <p>The returned array will be "safe" in that no references to it
 * are maintained by this set. (In other words, this method must
 * allocate a new array even if this set is backed by an array).
 * The caller is thus free to modify the returned array.
 *
 * <p>This method acts as bridge between array-based and collection-based
 * APIs.
 *
 * @return an array containing all the elements in this set
 */
 public Object[] toArray() {
 return al.toArray();
 }

 /**
 * Returns an array containing all of the elements in this set; the
 * runtime type of the returned array is that of the specified array.
 * If the set fits in the specified array, it is returned therein.
 * Otherwise, a new array is allocated with the runtime type of the
 * specified array and the size of this set.
 *
 * <p>If this set fits in the specified array with room to spare
 * (i.e., the array has more elements than this set), the element in
 * the array immediately following the end of the set is set to
 * {@code null}. (This is useful in determining the length of this
 * set <i>only</i> if the caller knows that this set does not contain
 * any null elements.)
 *
 * <p>If this set makes any guarantees as to what order its elements
 * are returned by its iterator, this method must return the elements
 * in the same order.
 *
 * <p>Like the {@link #toArray()} method, this method acts as bridge between
 * array-based and collection-based APIs. Further, this method allows
 * precise control over the runtime type of the output array, and may,
 * under certain circumstances, be used to save allocation costs.
 *
 * <p>Suppose {@code x} is a set known to contain only strings.
 * The following code can be used to dump the set into a newly allocated
 * array of {@code String}:
 *
 * <pre> {@code String[] y = x.toArray(new String[0]);}</pre>
 *
 * Note that {@code toArray(new Object[0])} is identical in function to
 * {@code toArray()}.
 *
 * @param a the array into which the elements of this set are to be
 * stored, if it is big enough; otherwise, a new array of the same
 * runtime type is allocated for this purpose.
 * @return an array containing all the elements in this set
 * @throws ArrayStoreException if the runtime type of the specified array
 * is not a supertype of the runtime type of every element in this
 * set
 * @throws NullPointerException if the specified array is null
 */
 public <T> T[] toArray(T[] a) {
 return al.toArray(a);
 }

 /**
 * Removes all of the elements from this set.
 * The set will be empty after this call returns.
 */
 public void clear() {
 al.clear();
 }

 /**
 * Removes the specified element from this set if it is present.
 * More formally, removes an element {@code e} such that
 * {@code Objects.equals(o, e)}, if this set contains such an element.
 * Returns {@code true} if this set contained the element (or
 * equivalently, if this set changed as a result of the call).
 * (This set will not contain the element once the call returns.)
 *
 * @param o object to be removed from this set, if present
 * @return {@code true} if this set contained the specified element
 */
 public boolean remove(Object o) {
 return al.remove(o);
 }

 /**
 * Adds the specified element to this set if it is not already present.
 * More formally, adds the specified element {@code e} to this set if
 * the set contains no element {@code e2} such that
 * {@code Objects.equals(e, e2)}.
 * If this set already contains the element, the call leaves the set
 * unchanged and returns {@code false}.
 *
 * @param e element to be added to this set
 * @return {@code true} if this set did not already contain the specified
 * element
 */
 public boolean add(E e) {
 return al.addIfAbsent(e);
 }

 /**
 * Returns {@code true} if this set contains all of the elements of the
 * specified collection. If the specified collection is also a set, this
 * method returns {@code true} if it is a <i>subset</i> of this set.
 *
 * @param c collection to be checked for containment in this set
 * @return {@code true} if this set contains all of the elements of the
 * specified collection
 * @throws NullPointerException if the specified collection is null
 * @see #contains(Object)
 */
 public boolean containsAll(Collection<?> c) {
 return (c instanceof Set)
 ? compareSets(al.getArray(), (Set<?>) c) >= 0
 : al.containsAll(c);
 }

 /**
 * Tells whether the objects in snapshot (regarded as a set) are a
 * superset of the given set.
 *
 * @return -1 if snapshot is not a superset, 0 if the two sets
 * contain precisely the same elements, and 1 if snapshot is a
 * proper superset of the given set
 */
 private static int compareSets(Object[] snapshot, Set<?> set) {
 // Uses O(n^2) algorithm, that is only appropriate for small
 // sets, which CopyOnWriteArraySets should be.
 //
 // Optimize up to O(n) if the two sets share a long common prefix,
 // as might happen if one set was created as a copy of the other set.

 final int len = snapshot.length;
 // Mark matched elements to avoid re-checking
 final boolean[] matched = new boolean[len];

 // j is the largest int with matched[i] true for { i | 0 <= i < j }
 int j = 0;
 outer: for (Object x : set) {
 for (int i = j; i < len; i++) {
 if (!matched[i] && Objects.equals(x, snapshot[i])) {
 matched[i] = true;
 if (i == j)
 do { j++; } while (j < len && matched[j]);
 continue outer;
 }
 }
 return -1;
 }
 return (j == len) ? 0 : 1;
 }

 /**
 * Adds all of the elements in the specified collection to this set if
 * they're not already present. If the specified collection is also a
 * set, the {@code addAll} operation effectively modifies this set so
 * that its value is the <i>union</i> of the two sets. The behavior of
 * this operation is undefined if the specified collection is modified
 * while the operation is in progress.
 *
 * @param c collection containing elements to be added to this set
 * @return {@code true} if this set changed as a result of the call
 * @throws NullPointerException if the specified collection is null
 * @see #add(Object)
 */
 public boolean addAll(Collection<? extends E> c) {
 return al.addAllAbsent(c) > 0;
 }

 /**
 * Removes from this set all of its elements that are contained in the
 * specified collection. If the specified collection is also a set,
 * this operation effectively modifies this set so that its value is the
 * <i>asymmetric set difference</i> of the two sets.
 *
 * @param c collection containing elements to be removed from this set
 * @return {@code true} if this set changed as a result of the call
 * @throws ClassCastException if the class of an element of this set
 * is incompatible with the specified collection
 * (<a href="{@docRoot}/java.base/java/util/Collection.html#optional-restrictions">optional</a>)
 * @throws NullPointerException if this set contains a null element and the
 * specified collection does not permit null elements
 * (<a href="{@docRoot}/java.base/java/util/Collection.html#optional-restrictions">optional</a>),
 * or if the specified collection is null
 * @see #remove(Object)
 */
 public boolean removeAll(Collection<?> c) {
 return al.removeAll(c);
 }

 /**
 * Retains only the elements in this set that are contained in the
 * specified collection. In other words, removes from this set all of
 * its elements that are not contained in the specified collection. If
 * the specified collection is also a set, this operation effectively
 * modifies this set so that its value is the <i>intersection</i> of the
 * two sets.
 *
 * @param c collection containing elements to be retained in this set
 * @return {@code true} if this set changed as a result of the call
 * @throws ClassCastException if the class of an element of this set
 * is incompatible with the specified collection
 * (<a href="{@docRoot}/java.base/java/util/Collection.html#optional-restrictions">optional</a>)
 * @throws NullPointerException if this set contains a null element and the
 * specified collection does not permit null elements
 * (<a href="{@docRoot}/java.base/java/util/Collection.html#optional-restrictions">optional</a>),
 * or if the specified collection is null
 * @see #remove(Object)
 */
 public boolean retainAll(Collection<?> c) {
 return al.retainAll(c);
 }

 /**
 * Returns an iterator over the elements contained in this set
 * in the order in which these elements were added.
 *
 * <p>The returned iterator provides a snapshot of the state of the set
 * when the iterator was constructed. No synchronization is needed while
 * traversing the iterator. The iterator does <em>NOT</em> support the
 * {@code remove} method.
 *
 * @return an iterator over the elements in this set
 */
 public Iterator<E> iterator() {
 return al.iterator();
 }

 /**
 * Compares the specified object with this set for equality.
 * Returns {@code true} if the specified object is the same object
 * as this object, or if it is also a {@link Set} and the elements
 * returned by an {@linkplain Set#iterator() iterator} over the
 * specified set are the same as the elements returned by an
 * iterator over this set. More formally, the two iterators are
 * considered to return the same elements if they return the same
 * number of elements and for every element {@code e1} returned by
 * the iterator over the specified set, there is an element
 * {@code e2} returned by the iterator over this set such that
 * {@code Objects.equals(e1, e2)}.
 *
 * @param o object to be compared for equality with this set
 * @return {@code true} if the specified object is equal to this set
 */
 public boolean equals(Object o) {
 return (o == this)
 || ((o instanceof Set)
 && compareSets(al.getArray(), (Set<?>) o) == 0);
 }

 /**
 * @throws NullPointerException {@inheritDoc}
 */
 public boolean removeIf(Predicate<? super E> filter) {
 return al.removeIf(filter);
 }

 /**
 * @throws NullPointerException {@inheritDoc}
 */
 public void forEach(Consumer<? super E> action) {
 al.forEach(action);
 }

 /**
 * Returns a {@link Spliterator} over the elements in this set in the order
 * in which these elements were added.
 *
 * <p>The {@code Spliterator} reports {@link Spliterator#IMMUTABLE},
 * {@link Spliterator#DISTINCT}, {@link Spliterator#SIZED}, and
 * {@link Spliterator#SUBSIZED}.
 *
 * <p>The spliterator provides a snapshot of the state of the set
 * when the spliterator was constructed. No synchronization is needed while
 * operating on the spliterator.
 *
 * @return a {@code Spliterator} over the elements in this set
 * @since 1.8
 */
 public Spliterator<E> spliterator() {
 return Spliterators.spliterator
 (al.getArray(), Spliterator.IMMUTABLE | Spliterator.DISTINCT);
 }
}