AbstractMergeCompletableOperator.java

/*
 * Copyright © 2018-2019, 2021 Apple Inc. and the ServiceTalk project authors
 *
 * 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.servicetalk.concurrent.api;

import static java.util.Objects.requireNonNull;

abstract class AbstractMergeCompletableOperator<T extends CompletableMergeSubscriber>
        extends AbstractNoHandleSubscribeCompletable
        implements CompletableOperator {

    private final Completable original;

    AbstractMergeCompletableOperator(Completable original) {
        this.original = requireNonNull(original);
    }

    @Override
    final void handleSubscribe(Subscriber subscriber, CapturedContext capturedContext,
                               AsyncContextProvider contextProvider) {
        // The AsyncContext needs to be preserved when ever we interact with the original Subscriber, so we wrap it here
        // with the original contextMap. Otherwise some other context may leak into this subscriber chain from the other
        // side of the asynchronous boundary.
        final Subscriber operatorSubscriber =
                contextProvider.wrapCompletableSubscriberAndCancellable(subscriber, capturedContext);
        T mergeSubscriber = apply(operatorSubscriber);
        original.delegateSubscribe(mergeSubscriber, capturedContext, contextProvider);
        doMerge(mergeSubscriber);
    }

    @Override
    public abstract T apply(Subscriber subscriber);

    /**
     * Called after the {@code original} {@link Completable} is subscribed and provides a way to subscribe to all other
     * {@link Completable}s that are to be merged with the {@code original} {@link Completable}.
     * @param subscriber {@link T} to be used to merge.
     */
    abstract void doMerge(T subscriber);
}