org.apache.flink.runtime.io.network.partition.ResultSubpartitionView Java Examples

/**
 * Tests that reading from a channel when after the partition has been
 * released are handled and don't lead to NPEs.
 */
@Test
public void testGetNextAfterPartitionReleased() throws Exception {
	ResultSubpartitionView subpartitionView = createResultSubpartitionView(false);
	TestingResultPartitionManager partitionManager = new TestingResultPartitionManager(subpartitionView);
	LocalInputChannel channel = createLocalInputChannel(new SingleInputGateBuilder().build(), partitionManager);

	channel.requestSubpartition(0);
	assertFalse(channel.getNextBuffer().isPresent());

	// release the subpartition view
	subpartitionView.releaseAllResources();

	try {
		channel.getNextBuffer();
		fail("Did not throw expected CancelTaskException");
	} catch (CancelTaskException ignored) {
	}

	channel.releaseAllResources();
	assertFalse(channel.getNextBuffer().isPresent());
}
 

@Test
public void testProducerFailedException() throws Exception {
	PartitionRequestQueue queue = new PartitionRequestQueue();

	ResultSubpartitionView view = new ReleasedResultSubpartitionView();

	ResultPartitionProvider partitionProvider =
		(partitionId, index, availabilityListener) -> view;

	EmbeddedChannel ch = new EmbeddedChannel(queue);

	CreditBasedSequenceNumberingViewReader seqView = new CreditBasedSequenceNumberingViewReader(new InputChannelID(), 2, queue);
	seqView.requestSubpartitionView(partitionProvider, new ResultPartitionID(), 0);
	// Add available buffer to trigger enqueue the erroneous view
	seqView.notifyDataAvailable();

	ch.runPendingTasks();

	// Read the enqueued msg
	Object msg = ch.readOutbound();

	assertEquals(msg.getClass(), NettyMessage.ErrorResponse.class);

	NettyMessage.ErrorResponse err = (NettyMessage.ErrorResponse) msg;
	assertTrue(err.cause instanceof CancelTaskException);
}
 

private void testBufferWriting(ResultSubpartitionView view) throws IOException {
	// setup
	ResultPartitionProvider partitionProvider =
		(partitionId, index, availabilityListener) -> view;

	final InputChannelID receiverId = new InputChannelID();
	final PartitionRequestQueue queue = new PartitionRequestQueue();
	final SequenceNumberingViewReader reader = new SequenceNumberingViewReader(receiverId, queue);
	final EmbeddedChannel channel = new EmbeddedChannel(queue);

	reader.requestSubpartitionView(partitionProvider, new ResultPartitionID(), 0);

	// notify about buffer availability and encode one buffer
	reader.notifyDataAvailable();

	channel.runPendingTasks();

	Object read = channel.readOutbound();
	assertNotNull(read);
	if (read instanceof NettyMessage.ErrorResponse) {
		((NettyMessage.ErrorResponse) read).cause.printStackTrace();
	}
	assertThat(read, instanceOf(NettyMessage.BufferResponse.class));
	read = channel.readOutbound();
	assertNull(read);
}
 

@Test(expected = CancelTaskException.class)
public void testProducerFailedException() throws Exception {
	ResultSubpartitionView view = mock(ResultSubpartitionView.class);
	when(view.isReleased()).thenReturn(true);
	when(view.getFailureCause()).thenReturn(new Exception("Expected test exception"));

	ResultPartitionManager partitionManager = mock(ResultPartitionManager.class);
	when(partitionManager
			.createSubpartitionView(any(ResultPartitionID.class), anyInt(), any(BufferAvailabilityListener.class)))
			.thenReturn(view);

	SingleInputGate inputGate = mock(SingleInputGate.class);
	BufferProvider bufferProvider = mock(BufferProvider.class);
	when(inputGate.getBufferProvider()).thenReturn(bufferProvider);

	LocalInputChannel ch = createLocalInputChannel(inputGate, partitionManager);

	ch.requestSubpartition(0);

	// Should throw an instance of CancelTaskException.
	ch.getNextBuffer();
}
 

@Test(expected = CancelTaskException.class)
public void testProducerFailedException() throws Exception {
	ResultSubpartitionView view = mock(ResultSubpartitionView.class);
	when(view.isReleased()).thenReturn(true);
	when(view.getFailureCause()).thenReturn(new Exception("Expected test exception"));

	ResultPartitionManager partitionManager = mock(ResultPartitionManager.class);
	when(partitionManager
			.createSubpartitionView(any(ResultPartitionID.class), anyInt(), any(BufferAvailabilityListener.class)))
			.thenReturn(view);

	SingleInputGate inputGate = mock(SingleInputGate.class);
	BufferProvider bufferProvider = mock(BufferProvider.class);
	when(inputGate.getBufferProvider()).thenReturn(bufferProvider);

	LocalInputChannel ch = createLocalInputChannel(
			inputGate, partitionManager, new Tuple2<>(0, 0));

	ch.requestSubpartition(0);

	// Should throw an instance of CancelTaskException.
	ch.getNextBuffer();
}
 

@Test(expected = CancelTaskException.class)
public void testProducerFailedException() throws Exception {
	ResultSubpartitionView view = mock(ResultSubpartitionView.class);
	when(view.isReleased()).thenReturn(true);
	when(view.getFailureCause()).thenReturn(new Exception("Expected test exception"));

	ResultPartitionManager partitionManager = mock(ResultPartitionManager.class);
	when(partitionManager
			.createSubpartitionView(any(ResultPartitionID.class), anyInt(), any(BufferAvailabilityListener.class)))
			.thenReturn(view);

	SingleInputGate inputGate = mock(SingleInputGate.class);
	BufferProvider bufferProvider = mock(BufferProvider.class);
	when(inputGate.getBufferProvider()).thenReturn(bufferProvider);

	LocalInputChannel ch = createLocalInputChannel(inputGate, partitionManager);

	ch.requestSubpartition(0);

	// Should throw an instance of CancelTaskException.
	ch.getNextBuffer();
}
 

@Test
public void testProducerFailedException() throws Exception {
	PartitionRequestQueue queue = new PartitionRequestQueue();

	ResultSubpartitionView view = new ReleasedResultSubpartitionView();

	ResultPartitionProvider partitionProvider =
		(partitionId, index, availabilityListener) -> view;

	EmbeddedChannel ch = new EmbeddedChannel(queue);

	CreditBasedSequenceNumberingViewReader seqView = new CreditBasedSequenceNumberingViewReader(new InputChannelID(), 2, queue);
	seqView.requestSubpartitionView(partitionProvider, new ResultPartitionID(), 0);
	// Add available buffer to trigger enqueue the erroneous view
	seqView.notifyDataAvailable();

	ch.runPendingTasks();

	// Read the enqueued msg
	Object msg = ch.readOutbound();

	assertEquals(msg.getClass(), NettyMessage.ErrorResponse.class);

	NettyMessage.ErrorResponse err = (NettyMessage.ErrorResponse) msg;
	assertTrue(err.cause instanceof CancelTaskException);
}
 

private void testBufferWriting(ResultSubpartitionView view) throws IOException {
	// setup
	ResultPartitionProvider partitionProvider =
		(partitionId, index, availabilityListener) -> view;

	final InputChannelID receiverId = new InputChannelID();
	final PartitionRequestQueue queue = new PartitionRequestQueue();
	final SequenceNumberingViewReader reader = new SequenceNumberingViewReader(receiverId, queue);
	final EmbeddedChannel channel = new EmbeddedChannel(queue);

	reader.requestSubpartitionView(partitionProvider, new ResultPartitionID(), 0);

	// notify about buffer availability and encode one buffer
	reader.notifyDataAvailable();

	channel.runPendingTasks();

	Object read = channel.readOutbound();
	assertNotNull(read);
	if (read instanceof NettyMessage.ErrorResponse) {
		((NettyMessage.ErrorResponse) read).cause.printStackTrace();
	}
	assertThat(read, instanceOf(NettyMessage.BufferResponse.class));
	read = channel.readOutbound();
	assertNull(read);
}
 

@Test
public void testProducerFailedException() throws Exception {
	PartitionRequestQueue queue = new PartitionRequestQueue();

	ResultSubpartitionView view = new ReleasedResultSubpartitionView();

	ResultPartitionProvider partitionProvider =
		(partitionId, index, availabilityListener) -> view;

	EmbeddedChannel ch = new EmbeddedChannel(queue);

	CreditBasedSequenceNumberingViewReader seqView = new CreditBasedSequenceNumberingViewReader(new InputChannelID(), 2, queue);
	seqView.requestSubpartitionView(partitionProvider, new ResultPartitionID(), 0);
	// Add available buffer to trigger enqueue the erroneous view
	seqView.notifyDataAvailable();

	ch.runPendingTasks();

	// Read the enqueued msg
	Object msg = ch.readOutbound();

	assertEquals(msg.getClass(), NettyMessage.ErrorResponse.class);

	NettyMessage.ErrorResponse err = (NettyMessage.ErrorResponse) msg;
	assertTrue(err.cause instanceof CancelTaskException);
}
 

private void verifyAvailability(RecordWriterDelegate writerDelegate) throws Exception {
	// writer is available at the beginning
	assertTrue(writerDelegate.isAvailable());
	assertTrue(writerDelegate.getAvailableFuture().isDone());

	// request one buffer from the local pool to make it unavailable
	RecordWriter recordWriter = writerDelegate.getRecordWriter(0);
	final BufferBuilder bufferBuilder = checkNotNull(recordWriter.getBufferBuilder(0));
	assertFalse(writerDelegate.isAvailable());
	CompletableFuture future = writerDelegate.getAvailableFuture();
	assertFalse(future.isDone());

	// recycle the buffer to make the local pool available again
	BufferBuilderTestUtils.fillBufferBuilder(bufferBuilder, 1).finish();
	ResultSubpartitionView readView = recordWriter.getTargetPartition().getSubpartition(0).createReadView(new NoOpBufferAvailablityListener());
	Buffer buffer = readView.getNextBuffer().buffer();

	buffer.recycleBuffer();
	assertTrue(future.isDone());
	assertTrue(writerDelegate.isAvailable());
	assertTrue(writerDelegate.getAvailableFuture().isDone());
}
 

private ResultSubpartitionView checkAndWaitForSubpartitionView() {
	// synchronizing on the request lock means this blocks until the asynchronous request
	// for the partition view has been completed
	// by then the subpartition view is visible or the channel is released
	synchronized (requestLock) {
		checkState(!isReleased, "released");
		checkState(subpartitionView != null, "Queried for a buffer before requesting the subpartition.");
		return subpartitionView;
	}
}
 

private void testBufferWriting(ResultSubpartitionView view) throws IOException {
	// setup
	ResultPartitionProvider partitionProvider =
		(partitionId, index, availabilityListener) -> view;

	final InputChannelID receiverId = new InputChannelID();
	final PartitionRequestQueue queue = new PartitionRequestQueue();
	final CreditBasedSequenceNumberingViewReader reader = new CreditBasedSequenceNumberingViewReader(
		receiverId,
		Integer.MAX_VALUE,
		queue);
	final EmbeddedChannel channel = new EmbeddedChannel(queue);

	reader.requestSubpartitionView(partitionProvider, new ResultPartitionID(), 0);

	// notify about buffer availability and encode one buffer
	reader.notifyDataAvailable();

	channel.runPendingTasks();

	Object read = channel.readOutbound();
	assertNotNull(read);
	if (read instanceof NettyMessage.ErrorResponse) {
		((NettyMessage.ErrorResponse) read).cause.printStackTrace();
	}
	assertThat(read, instanceOf(NettyMessage.BufferResponse.class));
	read = channel.readOutbound();
	assertNull(read);
}
 

@Override
public int unsynchronizedGetNumberOfQueuedBuffers() {
	ResultSubpartitionView view = subpartitionView;

	if (view != null) {
		return view.unsynchronizedGetNumberOfQueuedBuffers();
	}

	return 0;
}
 

/**
 * Releases the partition reader.
 */
@Override
void releaseAllResources() throws IOException {
	if (!isReleased) {
		isReleased = true;

		ResultSubpartitionView view = subpartitionView;
		if (view != null) {
			view.releaseAllResources();
			subpartitionView = null;
		}
	}
}
 

/**
 * Tests that reading from a channel when after the partition has been
 * released are handled and don't lead to NPEs.
 */
@Test
public void testGetNextAfterPartitionReleased() throws Exception {
	ResultSubpartitionView reader = mock(ResultSubpartitionView.class);
	SingleInputGate gate = mock(SingleInputGate.class);
	ResultPartitionManager partitionManager = mock(ResultPartitionManager.class);

	when(partitionManager.createSubpartitionView(
		any(ResultPartitionID.class),
		anyInt(),
		any(BufferAvailabilityListener.class))).thenReturn(reader);

	LocalInputChannel channel = createLocalInputChannel(gate, partitionManager);

	channel.requestSubpartition(0);

	// Null buffer but not released
	when(reader.getNextBuffer()).thenReturn(null);
	when(reader.isReleased()).thenReturn(false);

	assertFalse(channel.getNextBuffer().isPresent());

	// Null buffer and released
	when(reader.getNextBuffer()).thenReturn(null);
	when(reader.isReleased()).thenReturn(true);

	try {
		channel.getNextBuffer();
		fail("Did not throw expected CancelTaskException");
	} catch (CancelTaskException ignored) {
	}

	channel.releaseAllResources();
	assertFalse(channel.getNextBuffer().isPresent());
}
 

/**
 * Tests {@link PartitionRequestQueue#enqueueAvailableReader(NetworkSequenceViewReader)},
 * verifying the reader would be enqueued in the pipeline if the next sending buffer is an event
 * even though it has no available credits.
 */
@Test
public void testEnqueueReaderByNotifyingEventBuffer() throws Exception {
	// setup
	final ResultSubpartitionView view = new NextIsEventResultSubpartitionView();

	ResultPartitionProvider partitionProvider =
		(partitionId, index, availabilityListener) -> view;

	final InputChannelID receiverId = new InputChannelID();
	final PartitionRequestQueue queue = new PartitionRequestQueue();
	final CreditBasedSequenceNumberingViewReader reader = new CreditBasedSequenceNumberingViewReader(receiverId, 0, queue);
	final EmbeddedChannel channel = new EmbeddedChannel(queue);

	reader.requestSubpartitionView(partitionProvider, new ResultPartitionID(), 0);

	// block the channel so that we see an intermediate state in the test
	ByteBuf channelBlockingBuffer = blockChannel(channel);
	assertNull(channel.readOutbound());

	// Notify an available event buffer to trigger enqueue the reader
	reader.notifyDataAvailable();

	channel.runPendingTasks();

	// The reader is enqueued in the pipeline because the next buffer is an event, even though no credits are available
	assertThat(queue.getAvailableReaders(), contains(reader)); // contains only (this) one!
	assertEquals(0, reader.getNumCreditsAvailable());

	// Flush the buffer to make the channel writable again and see the final results
	channel.flush();
	assertSame(channelBlockingBuffer, channel.readOutbound());

	assertEquals(0, queue.getAvailableReaders().size());
	assertEquals(0, reader.getNumCreditsAvailable());
	assertNull(channel.readOutbound());
}
 

/**
 * Tests {@link PartitionRequestQueue#enqueueAvailableReader(NetworkSequenceViewReader)},
 * verifying the reader would be enqueued in the pipeline if the next sending buffer is an event
 * even though it has no available credits.
 */
@Test
public void testEnqueueReaderByNotifyingEventBuffer() throws Exception {
	// setup
	final ResultSubpartitionView view = new NextIsEventResultSubpartitionView();

	ResultPartitionProvider partitionProvider =
		(partitionId, index, availabilityListener) -> view;

	final InputChannelID receiverId = new InputChannelID();
	final PartitionRequestQueue queue = new PartitionRequestQueue();
	final CreditBasedSequenceNumberingViewReader reader = new CreditBasedSequenceNumberingViewReader(receiverId, 0, queue);
	final EmbeddedChannel channel = new EmbeddedChannel(queue);

	reader.requestSubpartitionView(partitionProvider, new ResultPartitionID(), 0);

	// block the channel so that we see an intermediate state in the test
	ByteBuf channelBlockingBuffer = blockChannel(channel);
	assertNull(channel.readOutbound());

	// Notify an available event buffer to trigger enqueue the reader
	reader.notifyDataAvailable();

	channel.runPendingTasks();

	// The reader is enqueued in the pipeline because the next buffer is an event, even though no credits are available
	assertThat(queue.getAvailableReaders(), contains(reader)); // contains only (this) one!
	assertEquals(0, reader.getNumCreditsAvailable());

	// Flush the buffer to make the channel writable again and see the final results
	channel.flush();
	assertSame(channelBlockingBuffer, channel.readOutbound());

	assertEquals(0, queue.getAvailableReaders().size());
	assertEquals(0, reader.getNumCreditsAvailable());
	assertNull(channel.readOutbound());
}
 

@Override
public int unsynchronizedGetNumberOfQueuedBuffers() {
	ResultSubpartitionView view = subpartitionView;

	if (view != null) {
		return view.unsynchronizedGetNumberOfQueuedBuffers();
	}

	return 0;
}
 

/**
 * Releases the partition reader.
 */
@Override
void releaseAllResources() throws IOException {
	if (!isReleased) {
		isReleased = true;

		ResultSubpartitionView view = subpartitionView;
		if (view != null) {
			view.releaseAllResources();
			subpartitionView = null;
		}
	}
}
 

private ResultSubpartitionView checkAndWaitForSubpartitionView() {
	// synchronizing on the request lock means this blocks until the asynchronous request
	// for the partition view has been completed
	// by then the subpartition view is visible or the channel is released
	synchronized (requestLock) {
		checkState(!isReleased, "released");
		checkState(subpartitionView != null, "Queried for a buffer before requesting the subpartition.");
		return subpartitionView;
	}
}
 

/**
 * Releases the partition reader.
 */
@Override
void releaseAllResources() throws IOException {
	if (!isReleased) {
		isReleased = true;

		ResultSubpartitionView view = subpartitionView;
		if (view != null) {
			view.releaseAllResources();
			subpartitionView = null;
		}
	}
}
 

/**
 * Tests {@link PartitionRequestQueue#enqueueAvailableReader(NetworkSequenceViewReader)},
 * verifying the reader would be enqueued in the pipeline if the next sending buffer is an event
 * even though it has no available credits.
 */
@Test
public void testEnqueueReaderByNotifyingEventBuffer() throws Exception {
	// setup
	final ResultSubpartitionView view = new NextIsEventResultSubpartitionView();

	ResultPartitionProvider partitionProvider =
		(partitionId, index, availabilityListener) -> view;

	final InputChannelID receiverId = new InputChannelID();
	final PartitionRequestQueue queue = new PartitionRequestQueue();
	final CreditBasedSequenceNumberingViewReader reader = new CreditBasedSequenceNumberingViewReader(receiverId, 0, queue);
	final EmbeddedChannel channel = new EmbeddedChannel(queue);

	reader.requestSubpartitionView(partitionProvider, new ResultPartitionID(), 0);

	// block the channel so that we see an intermediate state in the test
	ByteBuf channelBlockingBuffer = blockChannel(channel);
	assertNull(channel.readOutbound());

	// Notify an available event buffer to trigger enqueue the reader
	reader.notifyDataAvailable();

	channel.runPendingTasks();

	// The reader is enqueued in the pipeline because the next buffer is an event, even though no credits are available
	assertThat(queue.getAvailableReaders(), contains(reader)); // contains only (this) one!
	assertEquals(0, reader.getNumCreditsAvailable());

	// Flush the buffer to make the channel writable again and see the final results
	channel.flush();
	assertSame(channelBlockingBuffer, channel.readOutbound());

	assertEquals(0, queue.getAvailableReaders().size());
	assertEquals(0, reader.getNumCreditsAvailable());
	assertNull(channel.readOutbound());
}
 

@Override
Optional<BufferAndAvailability> getNextBuffer() throws IOException, InterruptedException {
	checkError();

	ResultSubpartitionView subpartitionView = this.subpartitionView;
	if (subpartitionView == null) {
		// There is a possible race condition between writing a EndOfPartitionEvent (1) and flushing (3) the Local
		// channel on the sender side, and reading EndOfPartitionEvent (2) and processing flush notification (4). When
		// they happen in that order (1 - 2 - 3 - 4), flush notification can re-enqueue LocalInputChannel after (or
		// during) it was released during reading the EndOfPartitionEvent (2).
		if (isReleased) {
			return Optional.empty();
		}

		// this can happen if the request for the partition was triggered asynchronously
		// by the time trigger
		// would be good to avoid that, by guaranteeing that the requestPartition() and
		// getNextBuffer() always come from the same thread
		// we could do that by letting the timer insert a special "requesting channel" into the input gate's queue
		subpartitionView = checkAndWaitForSubpartitionView();
	}

	BufferAndBacklog next = subpartitionView.getNextBuffer();

	if (next == null) {
		if (subpartitionView.isReleased()) {
			throw new CancelTaskException("Consumed partition " + subpartitionView + " has been released.");
		} else {
			return Optional.empty();
		}
	}

	numBytesIn.inc(next.buffer().getSizeUnsafe());
	numBuffersIn.inc();
	return Optional.of(new BufferAndAvailability(next.buffer(), next.isMoreAvailable(), next.buffersInBacklog()));
}
 

private static ResultSubpartitionView createResultSubpartitionView(boolean addBuffer) throws IOException {
	int bufferSize = 4096;
	ResultPartition parent = PartitionTestUtils.createPartition(
		ResultPartitionType.PIPELINED,
		NoOpFileChannelManager.INSTANCE,
		true,
		bufferSize);
	ResultSubpartition subpartition = parent.getAllPartitions()[0];
	if (addBuffer) {
		subpartition.add(BufferBuilderTestUtils.createFilledFinishedBufferConsumer(bufferSize));
	}
	return subpartition.createReadView(() -> {});
}
 

/**
 * Verifies that buffer is not compressed when getting from a {@link LocalInputChannel}.
 */
@Test
public void testGetBufferFromLocalChannelWhenCompressionEnabled() throws Exception {
	ResultSubpartitionView subpartitionView = createResultSubpartitionView(true);
	TestingResultPartitionManager partitionManager = new TestingResultPartitionManager(subpartitionView);
	LocalInputChannel channel = createLocalInputChannel(new SingleInputGateBuilder().build(), partitionManager);

	// request partition and get next buffer
	channel.requestSubpartition(0);
	Optional<InputChannel.BufferAndAvailability> bufferAndAvailability = channel.getNextBuffer();
	assertTrue(bufferAndAvailability.isPresent());
	assertFalse(bufferAndAvailability.get().buffer().isCompressed());
}
 

@Override
public ResultSubpartitionView createSubpartitionView(
		ResultPartitionID partitionId,
		int subpartitionIndex,
		BufferAvailabilityListener availabilityListener) throws IOException {
	++counter;
	return subpartitionView;
}
 

@Override
Optional<BufferAndAvailability> getNextBuffer() throws IOException, InterruptedException {
	checkError();

	ResultSubpartitionView subpartitionView = this.subpartitionView;
	if (subpartitionView == null) {
		// There is a possible race condition between writing a EndOfPartitionEvent (1) and flushing (3) the Local
		// channel on the sender side, and reading EndOfPartitionEvent (2) and processing flush notification (4). When
		// they happen in that order (1 - 2 - 3 - 4), flush notification can re-enqueue LocalInputChannel after (or
		// during) it was released during reading the EndOfPartitionEvent (2).
		if (isReleased) {
			return Optional.empty();
		}

		// this can happen if the request for the partition was triggered asynchronously
		// by the time trigger
		// would be good to avoid that, by guaranteeing that the requestPartition() and
		// getNextBuffer() always come from the same thread
		// we could do that by letting the timer insert a special "requesting channel" into the input gate's queue
		subpartitionView = checkAndWaitForSubpartitionView();
	}

	BufferAndBacklog next = subpartitionView.getNextBuffer();

	if (next == null) {
		if (subpartitionView.isReleased()) {
			throw new CancelTaskException("Consumed partition " + subpartitionView + " has been released.");
		} else {
			return Optional.empty();
		}
	}

	numBytesIn.inc(next.buffer().getSize());
	numBuffersIn.inc();
	return Optional.of(new BufferAndAvailability(next.buffer(), next.isMoreAvailable(), next.buffersInBacklog()));
}
 

private ResultSubpartitionView checkAndWaitForSubpartitionView() {
	// synchronizing on the request lock means this blocks until the asynchronous request
	// for the partition view has been completed
	// by then the subpartition view is visible or the channel is released
	synchronized (requestLock) {
		checkState(!isReleased, "released");
		checkState(subpartitionView != null, "Queried for a buffer before requesting the subpartition.");
		return subpartitionView;
	}
}
 

public TestingResultPartitionManager(ResultSubpartitionView subpartitionView) {
	this.subpartitionView = subpartitionView;
}
 

/**
 * Tests {@link PartitionRequestQueue#enqueueAvailableReader(NetworkSequenceViewReader)},
 * verifying the reader would be enqueued in the pipeline iff it has both available credits and buffers.
 */
@Test
public void testEnqueueReaderByNotifyingBufferAndCredit() throws Exception {
	// setup
	final ResultSubpartitionView view = new DefaultBufferResultSubpartitionView(10);

	ResultPartitionProvider partitionProvider =
		(partitionId, index, availabilityListener) -> view;

	final InputChannelID receiverId = new InputChannelID();
	final PartitionRequestQueue queue = new PartitionRequestQueue();
	final CreditBasedSequenceNumberingViewReader reader = new CreditBasedSequenceNumberingViewReader(receiverId, 0, queue);
	final EmbeddedChannel channel = new EmbeddedChannel(queue);

	reader.requestSubpartitionView(partitionProvider, new ResultPartitionID(), 0);
	queue.notifyReaderCreated(reader);

	// block the channel so that we see an intermediate state in the test
	ByteBuf channelBlockingBuffer = blockChannel(channel);
	assertNull(channel.readOutbound());

	// Notify available buffers to trigger enqueue the reader
	final int notifyNumBuffers = 5;
	for (int i = 0; i < notifyNumBuffers; i++) {
		reader.notifyDataAvailable();
	}

	channel.runPendingTasks();

	// the reader is not enqueued in the pipeline because no credits are available
	// -> it should still have the same number of pending buffers
	assertEquals(0, queue.getAvailableReaders().size());
	assertTrue(reader.hasBuffersAvailable());
	assertFalse(reader.isRegisteredAsAvailable());
	assertEquals(0, reader.getNumCreditsAvailable());

	// Notify available credits to trigger enqueue the reader again
	final int notifyNumCredits = 3;
	for (int i = 1; i <= notifyNumCredits; i++) {
		queue.addCreditOrResumeConsumption(receiverId, viewReader -> viewReader.addCredit(1));

		// the reader is enqueued in the pipeline because it has both available buffers and credits
		// since the channel is blocked though, we will not process anything and only enqueue the
		// reader once
		assertTrue(reader.isRegisteredAsAvailable());
		assertThat(queue.getAvailableReaders(), contains(reader)); // contains only (this) one!
		assertEquals(i, reader.getNumCreditsAvailable());
		assertTrue(reader.hasBuffersAvailable());
	}

	// Flush the buffer to make the channel writable again and see the final results
	channel.flush();
	assertSame(channelBlockingBuffer, channel.readOutbound());

	assertEquals(0, queue.getAvailableReaders().size());
	assertEquals(0, reader.getNumCreditsAvailable());
	assertTrue(reader.hasBuffersAvailable());
	assertFalse(reader.isRegisteredAsAvailable());
	for (int i = 1; i <= notifyNumCredits; i++) {
		assertThat(channel.readOutbound(), instanceOf(NettyMessage.BufferResponse.class));
	}
	assertNull(channel.readOutbound());
}