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Avoid deadlock consuming from blocking Iterator (#2204)
Motivation: The blocking streaming APIs allow for specifying a Iterator as input which is consumed by ServiceTalk. ServiceTalk assumes it can consume in batches from the same thread in order to make progress. However if the Iterator `next()` method is dependent on external input we may deadlock: - `PublisherAsBlockingIterable.onSubscribe(..)` does a `request(16)` - `FromIterablePublisher.request(..)` loops calling `hasNext()` and `next()` until demand is exhausted. Each loop iteration calls `subscriber.onNext(next())`. - The same thread looping in `FromIterablePublisher.request(..)` is also responsible for draining the queue in `PublisherAsBlockingIterable`. This means that no data will be sent downstream until `FromIterablePublisher` exits the loop. This maybe perceived as “dead lock” because no data is sent even if the `Iterable` provides an element. Modifications: - `FromIterablePublisher` and `FromBlockingIterablePublisher` check to unwrap from `PublisherAsBlockingIterable` if possible to directly access the underlying `Publisher`. This skips thee consumption via thee `Iterable` API and avoids the dead lock loop. Result: No more dead lock when using HTTP / gRPC API conversions and providing `Iterable` that is dependent upon external events to make progress.
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...k-http-netty/src/test/java/io/servicetalk/http/netty/BlockingStreamingHttpClientTest.java
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| /* | ||
| * Copyright © 2022 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.http.netty; | ||
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| import io.servicetalk.http.api.BlockingStreamingHttpClient; | ||
| import io.servicetalk.http.api.BlockingStreamingHttpResponse; | ||
| import io.servicetalk.http.api.HttpPayloadWriter; | ||
| import io.servicetalk.transport.api.ServerContext; | ||
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| import org.junit.jupiter.params.ParameterizedTest; | ||
| import org.junit.jupiter.params.provider.ValueSource; | ||
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| import java.util.ArrayList; | ||
| import java.util.Iterator; | ||
| import java.util.List; | ||
| import java.util.concurrent.CountDownLatch; | ||
| import java.util.concurrent.atomic.AtomicInteger; | ||
| import java.util.function.BooleanSupplier; | ||
| import java.util.function.Supplier; | ||
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| import static io.servicetalk.http.api.HttpSerializers.appSerializerAsciiFixLen; | ||
| import static io.servicetalk.transport.netty.internal.AddressUtils.localAddress; | ||
| import static io.servicetalk.transport.netty.internal.AddressUtils.serverHostAndPort; | ||
| import static io.servicetalk.utils.internal.PlatformDependent.throwException; | ||
| import static org.hamcrest.MatcherAssert.assertThat; | ||
| import static org.hamcrest.Matchers.equalTo; | ||
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| final class BlockingStreamingHttpClientTest { | ||
| @ParameterizedTest | ||
| @ValueSource(ints = {1, 100}) | ||
| void iterableSequentialConsumptionDoesNotDeadLock(int numItems) throws Exception { | ||
| try (ServerContext ctx = HttpServers.forAddress(localAddress(0)) | ||
| .listenBlockingStreamingAndAwait((ctx1, request, response) -> { | ||
| HttpPayloadWriter<String> output = response.sendMetaData(appSerializerAsciiFixLen()); | ||
| for (String input : request.payloadBody(appSerializerAsciiFixLen())) { | ||
| output.write(input); | ||
| } | ||
| output.close(); | ||
| }); | ||
| BlockingStreamingHttpClient client = HttpClients.forResolvedAddress(serverHostAndPort(ctx)) | ||
| .buildBlockingStreaming()) { | ||
| NextSuppliers<String> nextSuppliers = NextSuppliers.stringSuppliers(numItems); | ||
| // Allow first item in Iterator to return from next(). | ||
| nextSuppliers.countDownNextLatch(); | ||
| BlockingStreamingHttpResponse resp = client.request(client.get("/") | ||
| .payloadBody(new TestBlockingIterable<>(nextSuppliers, nextSuppliers), appSerializerAsciiFixLen())); | ||
| StringBuilder responseBody = new StringBuilder(numItems); | ||
| int i = 0; | ||
| for (String respChunk : resp.payloadBody(appSerializerAsciiFixLen())) { | ||
| // Goal is to ensure we can write each individual chunk independently without blocking threads or having | ||
| // to batch multiple items. As each chunk is echoed back, unblock the next one. | ||
| nextSuppliers.countDownNextLatch(); | ||
| responseBody.append(respChunk); | ||
| ++i; | ||
| } | ||
| assertThat("num items: " + i + " responseBody: " + responseBody, i, equalTo(numItems)); | ||
| } | ||
| } | ||
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| private static final class NextSuppliers<T> implements Supplier<T>, BooleanSupplier { | ||
| private final List<NextSupplier<T>> items; | ||
| private final AtomicInteger nextIndex = new AtomicInteger(); | ||
| private final AtomicInteger latchIndex = new AtomicInteger(); | ||
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| NextSuppliers(List<NextSupplier<T>> items) { | ||
| this.items = items; | ||
| } | ||
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| static NextSuppliers<String> stringSuppliers(final int numItems) { | ||
| List<NextSupplier<String>> items = new ArrayList<>(numItems); | ||
| for (int i = 0; i < numItems; ++i) { | ||
| items.add(new NextSupplier<>(String.valueOf(i))); | ||
| } | ||
| return new NextSuppliers<>(items); | ||
| } | ||
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| void countDownNextLatch() { | ||
| final int i = latchIndex.getAndIncrement(); | ||
| if (i < items.size()) { | ||
| items.get(i).latch.countDown(); | ||
| } | ||
| } | ||
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| @Override | ||
| public boolean getAsBoolean() { | ||
| return nextIndex.get() < items.size(); | ||
| } | ||
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| @Override | ||
| public T get() { | ||
| return items.get(nextIndex.getAndIncrement()).get(); | ||
| } | ||
| } | ||
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| private static final class NextSupplier<T> implements Supplier<T> { | ||
| final CountDownLatch latch = new CountDownLatch(1); | ||
| final T next; | ||
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| private NextSupplier(final T next) { | ||
| this.next = next; | ||
| } | ||
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| @Override | ||
| public T get() { | ||
| try { | ||
| latch.await(); | ||
| } catch (InterruptedException e) { | ||
| throwException(e); | ||
| } | ||
| return next; | ||
| } | ||
| } | ||
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| private static final class TestBlockingIterable<T> implements Iterable<T> { | ||
| private final BooleanSupplier hasNextSupplier; | ||
| private final Supplier<T> nextSupplier; | ||
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| private TestBlockingIterable(final BooleanSupplier hasNextSupplier, final Supplier<T> nextSupplier) { | ||
| this.hasNextSupplier = hasNextSupplier; | ||
| this.nextSupplier = nextSupplier; | ||
| } | ||
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| @Override | ||
| public Iterator<T> iterator() { | ||
| return new Iterator<T>() { | ||
| @Override | ||
| public boolean hasNext() { | ||
| return hasNextSupplier.getAsBoolean(); | ||
| } | ||
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| @Override | ||
| public T next() { | ||
| return nextSupplier.get(); | ||
| } | ||
| }; | ||
| } | ||
| } | ||
| } |