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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.subjects;

import rx.Observer;
import rx.functions.Action1;
import rx.internal.operators.NotificationLite;
import rx.subjects.SubjectSubscriptionManager.SubjectObserver;

/**
 * Subject that publishes only the last item observed to each {@link Observer} that has subscribed, when the
 * source {@code Observable} completes.
 * 
    
 * 
 * 
    
 * Example usage:
 * 
    
 * 
     {@code

  // observer will receive no onNext events because the subject.onCompleted() isn't called.
  AsyncSubject subject = AsyncSubject.create();
  subject.subscribe(observer);
  subject.onNext("one");
  subject.onNext("two");
  subject.onNext("three");

  // observer will receive "three" as the only onNext event.
  AsyncSubject subject = AsyncSubject.create();
  subject.subscribe(observer);
  subject.onNext("one");
  subject.onNext("two");
  subject.onNext("three");
  subject.onCompleted();

  } 
 * 
 * @param 
 *          the type of item expected to be observed by the Subject
 */
public final class AsyncSubject extends Subject {

    /**
     * Creates and returns a new {@code AsyncSubject}.
     * @param  the result value type
     * @return the new {@code AsyncSubject}
     */
    public static  AsyncSubject create() {
        final SubjectSubscriptionManager state = new SubjectSubscriptionManager();
        state.onTerminated = new Action1>() {
            @Override
            public void call(SubjectObserver o) {
                Object v = state.get();
                NotificationLite nl = state.nl;
                o.accept(v, nl);
                if (v == null || (!nl.isCompleted(v) && !nl.isError(v))) {
                    o.onCompleted();
                }
            }
        };
        return new AsyncSubject(state, state);
    }

    final SubjectSubscriptionManager state;
    volatile Object lastValue;
    private final NotificationLite nl = NotificationLite.instance();

    protected AsyncSubject(OnSubscribe onSubscribe, SubjectSubscriptionManager state) {
        super(onSubscribe);
        this.state = state;
    }

    @Override
    public void onCompleted() {
        if (state.active) {
            Object last = lastValue;
            if (last == null) {
                last = nl.completed();
            }
            for (SubjectObserver bo : state.terminate(last)) {
                if (last == nl.completed()) {
                    bo.onCompleted();
                } else {
                    bo.onNext(nl.getValue(last));
                    bo.onCompleted();
                }
            }
        }
    }

    @Override
    public void onError(final Throwable e) {
        if (state.active) {
            Object n = nl.error(e);
            for (SubjectObserver bo : state.terminate(n)) {
                bo.onError(e);
            }
        }
    }

    @Override
    public void onNext(T v) {
        lastValue = nl.next(v);
    }

}
    
    
    
    

    




    
    
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