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/**
 * Copyright 2014 Netflix, Inc.
 *
 * 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 rx.internal.subscriptions;

import java.util.concurrent.atomic.AtomicReference;

import rx.Subscription;
import rx.subscriptions.Subscriptions;

/**
 * A container of a Subscription that supports operations of SerialSubscription
 * and MultipleAssignmentSubscription via methods (update, replace) and extends
 * AtomicReference to reduce allocation count (beware the API leak of AtomicReference!).
 * @since 1.1.9
 */
public final class SequentialSubscription extends AtomicReference implements Subscription {

    /** */
    private static final long serialVersionUID = 995205034283130269L;

    /**
     * Create an empty SequentialSubscription.
     */
    public SequentialSubscription() {

    }

    /**
     * Create a SequentialSubscription with the given initial Subscription.
     * @param initial the initial Subscription, may be null
     */
    public SequentialSubscription(Subscription initial) {
        lazySet(initial);
    }

    /**
     * Returns the current contained Subscription (may be null).
     * 

(Remark: named as such because get() is final). * @return the current contained Subscription (may be null) */ public Subscription current() { Subscription current = super.get(); if (current == Unsubscribed.INSTANCE) { return Subscriptions.unsubscribed(); } return current; } /** * Atomically sets the contained Subscription to the provided next value and unsubscribes * the previous value or unsubscribes the next value if this container is unsubscribed. *

(Remark: named as such because set() is final). * @param next the next Subscription to contain, may be null * @return true if the update succeeded, false if the container was unsubscribed */ public boolean update(Subscription next) { for (;;) { Subscription current = get(); if (current == Unsubscribed.INSTANCE) { if (next != null) { next.unsubscribe(); } return false; } if (compareAndSet(current, next)) { if (current != null) { current.unsubscribe(); } return true; } } } /** * Atomically replaces the contained Subscription to the provided next value but * does not unsubscribe the previous value or unsubscribes the next value if this * container is unsubscribed. * @param next the next Subscription to contain, may be null * @return true if the update succeeded, false if the container was unsubscribed */ public boolean replace(Subscription next) { for (;;) { Subscription current = get(); if (current == Unsubscribed.INSTANCE) { if (next != null) { next.unsubscribe(); } return false; } if (compareAndSet(current, next)) { return true; } } } /** * Atomically tries to set the contained Subscription to the provided next value and unsubscribes * the previous value or unsubscribes the next value if this container is unsubscribed. *

* Unlike {@link #update(Subscription)}, this doesn't retry if the replace failed * because a concurrent operation changed the underlying contained object. * @param next the next Subscription to contain, may be null * @return true if the update succeeded, false if the container was unsubscribed */ public boolean updateWeak(Subscription next) { Subscription current = get(); if (current == Unsubscribed.INSTANCE) { if (next != null) { next.unsubscribe(); } return false; } if (compareAndSet(current, next)) { return true; } current = get(); if (next != null) { next.unsubscribe(); } return current == Unsubscribed.INSTANCE; } /** * Atomically tries to replace the contained Subscription to the provided next value but * does not unsubscribe the previous value or unsubscribes the next value if this container * is unsubscribed. *

* Unlike {@link #replace(Subscription)}, this doesn't retry if the replace failed * because a concurrent operation changed the underlying contained object. * @param next the next Subscription to contain, may be null * @return true if the update succeeded, false if the container was unsubscribed */ public boolean replaceWeak(Subscription next) { Subscription current = get(); if (current == Unsubscribed.INSTANCE) { if (next != null) { next.unsubscribe(); } return false; } if (compareAndSet(current, next)) { return true; } current = get(); if (current == Unsubscribed.INSTANCE) { if (next != null) { next.unsubscribe(); } return false; } return true; } @Override public void unsubscribe() { Subscription current = get(); if (current != Unsubscribed.INSTANCE) { current = getAndSet(Unsubscribed.INSTANCE); if (current != null && current != Unsubscribed.INSTANCE) { current.unsubscribe(); } } } @Override public boolean isUnsubscribed() { return get() == Unsubscribed.INSTANCE; } }





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