xtern commented on code in PR #1511: URL: https://github.com/apache/ignite-3/pull/1511#discussion_r1068092636
########## modules/sql-engine/src/main/java/org/apache/ignite/internal/sql/engine/util/ConcatPublisher.java: ########## @@ -0,0 +1,263 @@ +/* + * Licensed to the Apache Software Foundation (ASF) under one or more + * contributor license agreements. See the NOTICE file distributed with + * this work for additional information regarding copyright ownership. + * The ASF licenses this file to You 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 org.apache.ignite.internal.sql.engine.util; + +import java.lang.invoke.MethodHandles; +import java.lang.invoke.MethodHandles.Lookup; +import java.lang.invoke.VarHandle; +import java.util.Iterator; +import java.util.concurrent.Flow.Publisher; +import java.util.concurrent.Flow.Subscriber; +import java.util.concurrent.Flow.Subscription; +import java.util.concurrent.atomic.AtomicInteger; + + +/** + * Thread-safe realization of combine multiple publishers. Generally, start consuming a source once the previous source has terminated, + * building a chain. + */ +public class ConcatPublisher<T> implements Publisher<T> { + /** Iterator of upstream publishers. */ + private final Iterator<Publisher<? extends T>> sources; + + /** + * Constructor. + * + * @param sources Iterator of upstream publishers. + */ + public ConcatPublisher(Iterator<Publisher<? extends T>> sources) { + this.sources = sources; + } + + /** {@inheritDoc} */ + @Override + public void subscribe(Subscriber<? super T> downstream) { + ConcatCoordinator<T> subscription = new ConcatCoordinator<>(downstream, sources); + + downstream.onSubscribe(subscription); + subscription.drain(); + } + + /** + * Concatenation composite subscription. + */ + static final class ConcatCoordinator<T> extends SubscriptionArbiter implements Subscriber<T> { + /** Counter to prevent concurrent execution of a critical section. */ + private final AtomicInteger guardCntr = new AtomicInteger(); + + final Subscriber downstream; + + final Iterator<Publisher<? extends T>> sources; + + long consumed; + + ConcatCoordinator( + Subscriber downstream, + Iterator<Publisher<? extends T>> sources + ) { + this.downstream = downstream; + this.sources = sources; + } + + @Override + public void onSubscribe(Subscription s) { + setSubscription(s); + } + + @Override + public void onNext(T item) { + consumed++; + downstream.onNext(item); + } + + @Override + public void onError(Throwable throwable) { + downstream.onError(throwable); + } + + @Override + public void onComplete() { + drain(); + } + + void drain() { + if (guardCntr.getAndIncrement() == 0) { + do { + if (isCancelled()) { + return; + } + + if (!sources.hasNext()) { + downstream.onComplete(); + return; + } + + long c = consumed; + if (c != 0L) { + consumed = 0L; + setProduced(c); + } + + sources.next().subscribe(this); + + } while ((guardCntr.getAndDecrement() - 1) != 0); + } + } + } + + static class SubscriptionArbiter implements Subscription { Review Comment: We currently have only one class that inherits from `SubscriptionArbiter` - `ConcatCoordinator`. It seems we should just combine `ConcatCoordinator` with `SubscriptionArbiter` -- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. To unsubscribe, e-mail: notifications-unsubscr...@ignite.apache.org For queries about this service, please contact Infrastructure at: us...@infra.apache.org
