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	/*
	* 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.
	*/

	/*
	* This file is available under and governed by the GNU General Public
	* License version 2 only, as published by the Free Software Foundation.
	* However, the following notice accompanied the original version of this
	* file:
	*
	* 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);
	}
	}

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