MultipleAssignmentSubscription.java

/**
 * 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.subscriptions;

import java.util.concurrent.atomic.AtomicReference;

import rx.Observable;
import rx.Subscription;

/**
 * Subscription that can be checked for status such as in a loop inside an {@link Observable} to exit the loop if unsubscribed.
 * 
 * @see <a href="http://msdn.microsoft.com/en-us/library/system.reactive.disposables.multipleassignmentdisposable">Rx.Net equivalent MultipleAssignmentDisposable</a>
 */
public final class MultipleAssignmentSubscription implements Subscription {

    private static final State EMPTY = new State(false, Subscriptions.empty());
    private static final State DONE = new State(true, Subscriptions.empty());
    
    private final AtomicReference<State> state = new AtomicReference<State>(EMPTY);

    private static final class State {
        final boolean isUnsubscribed;
        final Subscription subscription;

        State(boolean u, Subscription s) {
            this.isUnsubscribed = u;
            this.subscription = s;
        }

        State set(Subscription s) {
            return new State(isUnsubscribed, s);
        }

    }

    @Override
    public boolean isUnsubscribed() {
        return state.get().isUnsubscribed;
    }

    @Override
    public void unsubscribe() {
        terminate(true);
    }

    @Deprecated
    public void setSubscription(Subscription s) {
        set(s);
    }

    public void set(Subscription s) {
        write(s, true);
    }

    /**
     * Sets the subscription but does not unsubscribe it when set on a terminated instance.
     * @param s the new subscription to attempt to set
     * @param unsubscribeOld unsubscribe s if the current instance is already terminated?
     */
    public void write(Subscription s, boolean unsubscribeOld) {
        if (s == null) {
            throw new IllegalArgumentException("Subscription can not be null");
        }
        State oldState;
        State newState;
        do {
            oldState = state.get();
            if (oldState.isUnsubscribed) {
                if (unsubscribeOld) {
                    s.unsubscribe();
                }
                return;
            } else {
                newState = oldState.set(s);
            }
        } while (!state.compareAndSet(oldState, newState));
    }
    /**
     * Terminate this subscription without unsubscribing from the current content.
     * @param unsubscribeOld unsubscribe the inner instance?
     */
    public void terminate(boolean unsubscribeOld) {
        State oldState = state.getAndSet(DONE);
        if (unsubscribeOld) {
            oldState.subscription.unsubscribe();
        }
    }

    @Deprecated
    public Subscription getSubscription() {
        return get();
    }

    public Subscription get() {
        return state.get().subscription;
    }

}