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/**
 * Copyright (c) 2016-present, RxJava Contributors.
 *
 * 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 io.reactivex.internal.subscriptions;

import io.reactivex.annotations.Nullable;
import org.reactivestreams.Subscriber;

import io.reactivex.internal.fuseable.QueueSubscription;

/**
 * An empty subscription that does nothing other than validates the request amount.
 */
public enum EmptySubscription implements QueueSubscription {
    /** A singleton, stateless instance. */
    INSTANCE;

    @Override
    public void request(long n) {
        SubscriptionHelper.validate(n);
    }

    @Override
    public void cancel() {
        // no-op
    }

    @Override
    public String toString() {
        return "EmptySubscription";
    }

    /**
     * Sets the empty subscription instance on the subscriber and then
     * calls onError with the supplied error.
     *
     * 

Make sure this is only called if the subscriber hasn't received a * subscription already (there is no way of telling this). * * @param e the error to deliver to the subscriber * @param s the target subscriber */ public static void error(Throwable e, Subscriber s) { s.onSubscribe(INSTANCE); s.onError(e); } /** * Sets the empty subscription instance on the subscriber and then * calls onComplete. * *

Make sure this is only called if the subscriber hasn't received a * subscription already (there is no way of telling this). * * @param s the target subscriber */ public static void complete(Subscriber s) { s.onSubscribe(INSTANCE); s.onComplete(); } @Nullable @Override public Object poll() { return null; // always empty } @Override public boolean isEmpty() { return true; } @Override public void clear() { // nothing to do } @Override public int requestFusion(int mode) { return mode & ASYNC; // accept async mode: an onComplete or onError will be signalled after anyway } @Override public boolean offer(Object value) { throw new UnsupportedOperationException("Should not be called!"); } @Override public boolean offer(Object v1, Object v2) { throw new UnsupportedOperationException("Should not be called!"); } }