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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.operators;

import java.util.Queue;
import java.util.concurrent.atomic.AtomicInteger;
import java.util.concurrent.atomic.AtomicLong;

import rx.Observable.Operator;
import rx.Producer;
import rx.Scheduler;
import rx.Subscriber;
import rx.Subscription;
import rx.exceptions.MissingBackpressureException;
import rx.functions.Action0;
import rx.internal.util.RxRingBuffer;
import rx.internal.util.SynchronizedQueue;
import rx.internal.util.unsafe.SpscArrayQueue;
import rx.internal.util.unsafe.UnsafeAccess;
import rx.schedulers.ImmediateScheduler;
import rx.schedulers.TrampolineScheduler;

/**
 * Delivers events on the specified {@code Scheduler} asynchronously via an unbounded buffer.
 * 
 * 
 * 
 * @param 
 *            the transmitted value type
 */
public final class OperatorObserveOn implements Operator {

    private final Scheduler scheduler;

    /**
     * @param scheduler
     */
    public OperatorObserveOn(Scheduler scheduler) {
        this.scheduler = scheduler;
    }

    @Override
    public Subscriber call(Subscriber child) {
        if (scheduler instanceof ImmediateScheduler) {
            // avoid overhead, execute directly
            return child;
        } else if (scheduler instanceof TrampolineScheduler) {
            // avoid overhead, execute directly
            return child;
        } else {
            ObserveOnSubscriber parent = new ObserveOnSubscriber(scheduler, child);
            parent.init();
            return parent;
        }
    }

    /** Observe through individual queue per observer. */
    private static final class ObserveOnSubscriber extends Subscriber {
        final Subscriber child;
        final Scheduler.Worker recursiveScheduler;
        final ScheduledUnsubscribe scheduledUnsubscribe;
        final NotificationLite on = NotificationLite.instance();

        final Queue queue;
        
        // the status of the current stream
        volatile boolean finished = false;

        final AtomicLong requested = new AtomicLong();
        
        final AtomicLong counter = new AtomicLong();
        
        volatile Throwable error;

        // do NOT pass the Subscriber through to couple the subscription chain ... unsubscribing on the parent should
        // not prevent anything downstream from consuming, which will happen if the Subscription is chained
        public ObserveOnSubscriber(Scheduler scheduler, Subscriber child) {
            this.child = child;
            this.recursiveScheduler = scheduler.createWorker();
            if (UnsafeAccess.isUnsafeAvailable()) {
                queue = new SpscArrayQueue(RxRingBuffer.SIZE);
            } else {
                queue = new SynchronizedQueue(RxRingBuffer.SIZE);
            }
            this.scheduledUnsubscribe = new ScheduledUnsubscribe(recursiveScheduler);
        }
        
        void init() {
            // don't want this code in the constructor because `this` can escape through the 
            // setProducer call
            child.add(scheduledUnsubscribe);
            child.setProducer(new Producer() {

                @Override
                public void request(long n) {
                    BackpressureUtils.getAndAddRequest(requested, n);
                    schedule();
                }

            });
            child.add(recursiveScheduler);
            child.add(this);
        }

        @Override
        public void onStart() {
            // signal that this is an async operator capable of receiving this many
            request(RxRingBuffer.SIZE);
        }

        @Override
        public void onNext(final T t) {
            if (isUnsubscribed()) {
                return;
            }
            if (!queue.offer(on.next(t))) {
                onError(new MissingBackpressureException());
                return;
            }
            schedule();
        }

        @Override
        public void onCompleted() {
            if (isUnsubscribed() || finished) {
                return;
            }
            finished = true;
            schedule();
        }

        @Override
        public void onError(final Throwable e) {
            if (isUnsubscribed() || finished) {
                return;
            }
            error = e;
            // unsubscribe eagerly since time will pass before the scheduled onError results in an unsubscribe event
            unsubscribe();
            finished = true;
            // polling thread should skip any onNext still in the queue
            schedule();
        }

        final Action0 action = new Action0() {

            @Override
            public void call() {
                pollQueue();
            }

        };

        protected void schedule() {
            if (counter.getAndIncrement() == 0) {
                recursiveScheduler.schedule(action);
            }
        }

        // only execute this from schedule()
        void pollQueue() {
            int emitted = 0;
            final AtomicLong localRequested = this.requested;
            final AtomicLong localCounter = this.counter;
            do {
                localCounter.set(1);
                long produced = 0;
                long r = localRequested.get();
                for (;;) {
                    if (child.isUnsubscribed())
                        return;
                    Throwable error;
                    if (finished) {
                        if ((error = this.error) != null) {
                            // errors shortcut the queue so 
                            // release the elements in the queue for gc
                            queue.clear();
                            child.onError(error);
                            return;
                        } else
                        if (queue.isEmpty()) {
                            child.onCompleted();
                            return;
                        }
                    }
                    if (r > 0) {
                        Object o = queue.poll();
                        if (o != null) {
                            child.onNext(on.getValue(o));
                            r--;
                            emitted++;
                            produced++;
                        } else {
                            break;
                        }
                    } else {
                        break;
                    }
                }
                if (produced > 0 && localRequested.get() != Long.MAX_VALUE) {
                    localRequested.addAndGet(-produced);
                }
            } while (localCounter.decrementAndGet() > 0);
            if (emitted > 0) {
                request(emitted);
            }
        }
    }

    static final class ScheduledUnsubscribe extends AtomicInteger implements Subscription {
        final Scheduler.Worker worker;
        volatile boolean unsubscribed = false;

        public ScheduledUnsubscribe(Scheduler.Worker worker) {
            this.worker = worker;
        }

        @Override
        public boolean isUnsubscribed() {
            return unsubscribed;
        }

        @Override
        public void unsubscribe() {
            if (getAndSet(1) == 0) {
                worker.schedule(new Action0() {
                    @Override
                    public void call() {
                        worker.unsubscribe();
                        unsubscribed = true;
                    }
                });
            }
        }

    }
}
    
    
    
    

    




    
    
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