A multiplexed output can either be immediate or deferred. Watermark updates on an immediate + * output will potentially directly affect the combined watermark state, which will be forwarded to + * the underlying output immediately. Watermark updates on a deferred output will only update an + * internal state but not directly update the combined watermark state. Only when {@link + * #onPeriodicEmit()} is called will the deferred updates be combined and forwarded to the + * underlying output. + * + *
For registering a new multiplexed output, you must first call {@link #registerNewOutput()} + * and then call {@link #getImmediateOutput(int)} or {@link #getDeferredOutput(int)} with the output + * ID you get from that. You can get both an immediate and deferred output for a given output ID, + * you can also call the getters multiple times. + * + *
WARNING:This class is not thread safe.
+ */
+@Internal
+public class WatermarkOutputMultiplexer {
+
+ /**
+ * The {@link WatermarkOutput} that we use to emit our multiplexed watermark updates. We assume
+ * that outside code holds a coordinating lock so we don't lock in this class when accessing
+ * this {@link WatermarkOutput}.
+ */
+ private final WatermarkOutput underlyingOutput;
+
+ /** The id to use for the next registered output. */
+ private int nextOutputId = 0;
+
+ /** The combined watermark over the per-output watermarks. */
+ private long combinedWatermark = Long.MIN_VALUE;
+
+ /**
+ * Map view, to allow finding them when requesting the {@link WatermarkOutput} for a given id.
+ */
+ private final Map >See {@link WatermarkOutputMultiplexer} for a description of immediate and deferred
+ * outputs.
+ */
+ public WatermarkOutput getImmediateOutput(int outputId) {
+ Preconditions.checkArgument(
+ watermarkPerOutputId.containsKey(outputId),
+ "no output registered under id " + outputId);
+
+ OutputState outputState = watermarkPerOutputId.get(outputId);
+ return new ImmediateOutput(outputState);
+ }
+
+ /**
+ * Returns a deferred {@link WatermarkOutput} for the given output ID.
+ *
+ * >See {@link WatermarkOutputMultiplexer} for a description of immediate and deferred
+ * outputs.
+ */
+ public WatermarkOutput getDeferredOutput(int outputId) {
+ Preconditions.checkArgument(
+ watermarkPerOutputId.containsKey(outputId),
+ "no output registered under id " + outputId);
+
+ OutputState outputState = watermarkPerOutputId.get(outputId);
+ return new DeferredOutput(outputState);
+ }
+
+ /**
+ * Tells the {@link WatermarkOutputMultiplexer} to combine all outstanding deferred watermark
+ * updates and possibly emit a new update to the underlying {@link WatermarkOutput}.
+ */
+ public void onPeriodicEmit() {
+ updateCombinedWatermark();
+ }
+
+ /**
+ * Checks whether we need to update the combined watermark. Should be called when a newly
+ * emitted per-output watermark is higher than the max so far or if we need to combined the
+ * deferred per-output updates.
+ */
+ private void updateCombinedWatermark() {
+ long minimumOverAllOutputs = Long.MAX_VALUE;
+
+ boolean hasOutputs = false;
+ boolean allIdle = true;
+ for (OutputState outputState : watermarkOutputs) {
+ if (!outputState.isIdle()) {
+ minimumOverAllOutputs = Math.min(minimumOverAllOutputs, outputState.getWatermark());
+ allIdle = false;
+ }
+ hasOutputs = true;
+ }
+
+ // if we don't have any outputs minimumOverAllOutputs is not valid, it's still
+ // at its initial Long.MAX_VALUE state and we must not emit that
+ if (!hasOutputs) {
+ return;
+ }
+
+ if (allIdle) {
+ underlyingOutput.markIdle();
+ } else if (minimumOverAllOutputs > combinedWatermark) {
+ combinedWatermark = minimumOverAllOutputs;
+ underlyingOutput.emitWatermark(new Watermark(minimumOverAllOutputs));
+ }
+ }
+
+ /**
+ * Per-output watermark state.
+ */
+ private static class OutputState {
+ private volatile long watermark = Long.MIN_VALUE;
+ private volatile boolean idle = false;
+
+ /**
+ * Returns the current watermark timestamp. This will throw {@link IllegalStateException} if
+ * the output is currently idle.
+ */
+ public long getWatermark() {
+ checkState(!idle, "Output is idle.");
+ return watermark;
+ }
+
+ /**
+ * Returns true if the watermark was advanced, that is if the new watermark is larger than
+ * the previous one.
+ *
+ * Setting a watermark will clear the idleness flag.
+ */
+ public boolean setWatermark(long watermark) {
+ this.idle = false;
+ if (watermark > this.watermark) {
+ this.watermark = watermark;
+ return true;
+ } else {
+ return false;
+ }
+ }
+
+ public boolean isIdle() {
+ return idle;
+ }
+
+ public void setIdle(boolean idle) {
+ this.idle = idle;
+ }
+ }
+
+ /**
+ * Updating the state of an immediate output can possible lead to a combined watermark update to
+ * the underlying {@link WatermarkOutput}.
+ */
+ private class ImmediateOutput implements WatermarkOutput {
+
+ private final OutputState state;
+
+ public ImmediateOutput(OutputState state) {
+ this.state = state;
+ }
+
+ @Override
+ public void emitWatermark(Watermark watermark) {
+ long timestamp = watermark.getTimestamp();
+ boolean wasUpdated = state.setWatermark(timestamp);
+
+ // if it's higher than the max watermark so far we might have to update the
+ // combined watermark
+ if (wasUpdated && timestamp > combinedWatermark) {
+ updateCombinedWatermark();
+ }
+ }
+
+ @Override
+ public void markIdle() {
+ state.setIdle(true);
+
+ // this can always lead to an advancing watermark. We don't know if this output
+ // was holding back the watermark or not.
+ updateCombinedWatermark();
+ }
+ }
+
+ /**
+ * Updating the state of a deferred output will never lead to a combined watermark update. Only
+ * when {@link WatermarkOutputMultiplexer#onPeriodicEmit()} is called will the deferred updates
+ * be combined into a potential combined update of the underlying {@link WatermarkOutput}.
+ */
+ private static class DeferredOutput implements WatermarkOutput {
+
+ private final OutputState state;
+
+ public DeferredOutput(OutputState state) {
+ this.state = state;
+ }
+
+ @Override
+ public void emitWatermark(Watermark watermark) {
+ state.setWatermark(watermark.getTimestamp());
+ }
+
+ @Override
+ public void markIdle() {
+ state.setIdle(true);
+ }
+ }
+}
diff --git a/flink-core/src/test/java/org/apache/flink/api/common/eventtime/WatermarkOutputMultiplexerTest.java b/flink-core/src/test/java/org/apache/flink/api/common/eventtime/WatermarkOutputMultiplexerTest.java
new file mode 100644
index 0000000000000000000000000000000000000000..224bf482f709d77fd46891f1278e1238b388d965
--- /dev/null
+++ b/flink-core/src/test/java/org/apache/flink/api/common/eventtime/WatermarkOutputMultiplexerTest.java
@@ -0,0 +1,318 @@
+/*
+ * 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.flink.api.common.eventtime;
+
+import org.junit.Test;
+
+import static org.apache.flink.api.common.eventtime.WatermarkMatchers.watermark;
+import static org.hamcrest.CoreMatchers.is;
+import static org.hamcrest.CoreMatchers.nullValue;
+import static org.junit.Assert.assertThat;
+
+/**
+ * Tests for the {@link WatermarkOutputMultiplexer}.
+ */
+public class WatermarkOutputMultiplexerTest {
+
+ @Test
+ public void singleImmediateWatermark() {
+ TestingWatermarkOutput underlyingWatermarkOutput = createTestingWatermarkOutput();
+ WatermarkOutputMultiplexer multiplexer =
+ new WatermarkOutputMultiplexer(underlyingWatermarkOutput);
+
+ WatermarkOutput watermarkOutput = createImmediateOutput(multiplexer);
+
+ watermarkOutput.emitWatermark(new Watermark(0));
+
+ assertThat(underlyingWatermarkOutput.lastWatermark(), is(watermark(0)));
+ assertThat(underlyingWatermarkOutput.isIdle(), is(false));
+ }
+
+ @Test
+ public void singleImmediateIdleness() {
+ TestingWatermarkOutput underlyingWatermarkOutput = createTestingWatermarkOutput();
+ WatermarkOutputMultiplexer multiplexer =
+ new WatermarkOutputMultiplexer(underlyingWatermarkOutput);
+
+ WatermarkOutput watermarkOutput = createImmediateOutput(multiplexer);
+
+ watermarkOutput.markIdle();
+
+ assertThat(underlyingWatermarkOutput.lastWatermark(), nullValue());
+ assertThat(underlyingWatermarkOutput.isIdle(), is(true));
+ }
+
+ @Test
+ public void singleImmediateWatermarkAfterIdleness() {
+ TestingWatermarkOutput underlyingWatermarkOutput = createTestingWatermarkOutput();
+ WatermarkOutputMultiplexer multiplexer =
+ new WatermarkOutputMultiplexer(underlyingWatermarkOutput);
+
+ WatermarkOutput watermarkOutput = createImmediateOutput(multiplexer);
+
+ watermarkOutput.markIdle();
+ assertThat(underlyingWatermarkOutput.isIdle(), is(true));
+
+ watermarkOutput.emitWatermark(new Watermark(0));
+
+ assertThat(underlyingWatermarkOutput.lastWatermark(), is(watermark(0)));
+ assertThat(underlyingWatermarkOutput.isIdle(), is(false));
+ }
+
+ @Test
+ public void multipleImmediateWatermark() {
+ TestingWatermarkOutput underlyingWatermarkOutput = createTestingWatermarkOutput();
+ WatermarkOutputMultiplexer multiplexer =
+ new WatermarkOutputMultiplexer(underlyingWatermarkOutput);
+
+ WatermarkOutput watermarkOutput1 = createImmediateOutput(multiplexer);
+ WatermarkOutput watermarkOutput2 = createImmediateOutput(multiplexer);
+ WatermarkOutput watermarkOutput3 = createImmediateOutput(multiplexer);
+
+ watermarkOutput1.emitWatermark(new Watermark(2));
+ watermarkOutput2.emitWatermark(new Watermark(5));
+ watermarkOutput3.markIdle();
+
+ assertThat(underlyingWatermarkOutput.lastWatermark(), is(watermark(2)));
+ assertThat(underlyingWatermarkOutput.isIdle(), is(false));
+ }
+
+ @Test
+ public void whenImmediateOutputBecomesIdleWatermarkAdvances() {
+ TestingWatermarkOutput underlyingWatermarkOutput = createTestingWatermarkOutput();
+ WatermarkOutputMultiplexer multiplexer =
+ new WatermarkOutputMultiplexer(underlyingWatermarkOutput);
+
+ WatermarkOutput watermarkOutput1 = createImmediateOutput(multiplexer);
+ WatermarkOutput watermarkOutput2 = createImmediateOutput(multiplexer);
+
+ watermarkOutput1.emitWatermark(new Watermark(2));
+ watermarkOutput2.emitWatermark(new Watermark(5));
+
+ assertThat(underlyingWatermarkOutput.lastWatermark(), is(watermark(2)));
+
+ watermarkOutput1.markIdle();
+
+ assertThat(underlyingWatermarkOutput.lastWatermark(), is(watermark(5)));
+ }
+
+ @Test
+ public void combinedWatermarkDoesNotRegressWhenIdleOutputRegresses() {
+ TestingWatermarkOutput underlyingWatermarkOutput = createTestingWatermarkOutput();
+ WatermarkOutputMultiplexer multiplexer =
+ new WatermarkOutputMultiplexer(underlyingWatermarkOutput);
+
+ WatermarkOutput watermarkOutput1 = createImmediateOutput(multiplexer);
+ WatermarkOutput watermarkOutput2 = createImmediateOutput(multiplexer);
+
+ watermarkOutput1.emitWatermark(new Watermark(2));
+ watermarkOutput2.emitWatermark(new Watermark(5));
+ watermarkOutput1.markIdle();
+
+ assertThat(underlyingWatermarkOutput.lastWatermark(), is(watermark(5)));
+
+ watermarkOutput1.emitWatermark(new Watermark(3));
+
+ assertThat(underlyingWatermarkOutput.lastWatermark(), is(watermark(5)));
+ }
+
+ /**
+ * This test makes sure that we don't output any update if there are zero outputs. Due to how
+ * aggregation of deferred updates in the KafkaConsumer works we had a bug there that caused a
+ * Long.MAX_VALUE watermark to be emitted in case of zero partitions.
+ */
+ @Test
+ public void noCombinedDeferredUpdateWhenWeHaveZeroOutputs() {
+ TestingWatermarkOutput underlyingWatermarkOutput = createTestingWatermarkOutput();
+ WatermarkOutputMultiplexer multiplexer =
+ new WatermarkOutputMultiplexer(underlyingWatermarkOutput);
+
+ multiplexer.onPeriodicEmit();
+
+ assertThat(underlyingWatermarkOutput.lastWatermark(), is(nullValue()));
+ }
+
+ @Test
+ public void deferredOutputDoesNotImmediatelyAdvanceWatermark() {
+ TestingWatermarkOutput underlyingWatermarkOutput = createTestingWatermarkOutput();
+ WatermarkOutputMultiplexer multiplexer =
+ new WatermarkOutputMultiplexer(underlyingWatermarkOutput);
+
+ WatermarkOutput watermarkOutput1 = createDeferredOutput(multiplexer);
+ WatermarkOutput watermarkOutput2 = createDeferredOutput(multiplexer);
+
+ watermarkOutput1.emitWatermark(new Watermark(0));
+ watermarkOutput2.emitWatermark(new Watermark(1));
+
+ assertThat(underlyingWatermarkOutput.lastWatermark(), nullValue());
+
+ multiplexer.onPeriodicEmit();
+
+ assertThat(underlyingWatermarkOutput.lastWatermark(), is(watermark(0)));
+ }
+
+ @Test
+ public void singleDeferredWatermark() {
+ TestingWatermarkOutput underlyingWatermarkOutput = createTestingWatermarkOutput();
+ WatermarkOutputMultiplexer multiplexer =
+ new WatermarkOutputMultiplexer(underlyingWatermarkOutput);
+
+ WatermarkOutput watermarkOutput = createDeferredOutput(multiplexer);
+
+ watermarkOutput.emitWatermark(new Watermark(0));
+ multiplexer.onPeriodicEmit();
+
+ assertThat(underlyingWatermarkOutput.lastWatermark(), is(watermark(0)));
+ assertThat(underlyingWatermarkOutput.isIdle(), is(false));
+ }
+
+ @Test
+ public void singleDeferredIdleness() {
+ TestingWatermarkOutput underlyingWatermarkOutput = createTestingWatermarkOutput();
+ WatermarkOutputMultiplexer multiplexer =
+ new WatermarkOutputMultiplexer(underlyingWatermarkOutput);
+
+ WatermarkOutput watermarkOutput = createDeferredOutput(multiplexer);
+
+ watermarkOutput.markIdle();
+ multiplexer.onPeriodicEmit();
+
+ assertThat(underlyingWatermarkOutput.lastWatermark(), nullValue());
+ assertThat(underlyingWatermarkOutput.isIdle(), is(true));
+ }
+
+ @Test
+ public void singleDeferredWatermarkAfterIdleness() {
+ TestingWatermarkOutput underlyingWatermarkOutput = createTestingWatermarkOutput();
+ WatermarkOutputMultiplexer multiplexer =
+ new WatermarkOutputMultiplexer(underlyingWatermarkOutput);
+
+ WatermarkOutput watermarkOutput = createDeferredOutput(multiplexer);
+
+ watermarkOutput.markIdle();
+ multiplexer.onPeriodicEmit();
+
+ assertThat(underlyingWatermarkOutput.isIdle(), is(true));
+
+ watermarkOutput.emitWatermark(new Watermark(0));
+ multiplexer.onPeriodicEmit();
+
+ assertThat(underlyingWatermarkOutput.lastWatermark(), is(watermark(0)));
+ assertThat(underlyingWatermarkOutput.isIdle(), is(false));
+ }
+
+ @Test
+ public void multipleDeferredWatermark() {
+ TestingWatermarkOutput underlyingWatermarkOutput = createTestingWatermarkOutput();
+ WatermarkOutputMultiplexer multiplexer =
+ new WatermarkOutputMultiplexer(underlyingWatermarkOutput);
+
+ WatermarkOutput watermarkOutput1 = createDeferredOutput(multiplexer);
+ WatermarkOutput watermarkOutput2 = createDeferredOutput(multiplexer);
+ WatermarkOutput watermarkOutput3 = createDeferredOutput(multiplexer);
+
+ watermarkOutput1.emitWatermark(new Watermark(2));
+ watermarkOutput2.emitWatermark(new Watermark(5));
+ watermarkOutput3.markIdle();
+
+ multiplexer.onPeriodicEmit();
+
+ assertThat(underlyingWatermarkOutput.lastWatermark(), is(watermark(2)));
+ assertThat(underlyingWatermarkOutput.isIdle(), is(false));
+ }
+
+ @Test
+ public void immediateUpdatesTakeDeferredUpdatesIntoAccount() {
+ TestingWatermarkOutput underlyingWatermarkOutput = createTestingWatermarkOutput();
+ WatermarkOutputMultiplexer multiplexer =
+ new WatermarkOutputMultiplexer(underlyingWatermarkOutput);
+
+ WatermarkOutput immediateOutput = createImmediateOutput(multiplexer);
+ WatermarkOutput deferredOutput = createDeferredOutput(multiplexer);
+
+ deferredOutput.emitWatermark(new Watermark(5));
+
+ assertThat(underlyingWatermarkOutput.lastWatermark(), is(nullValue()));
+
+ immediateOutput.emitWatermark(new Watermark(2));
+
+ assertThat(underlyingWatermarkOutput.lastWatermark(), is(watermark(2)));
+ }
+
+ @Test
+ public void immediateUpdateOnSameOutputAsDeferredUpdateDoesNotRegress() {
+ TestingWatermarkOutput underlyingWatermarkOutput = createTestingWatermarkOutput();
+ WatermarkOutputMultiplexer multiplexer =
+ new WatermarkOutputMultiplexer(underlyingWatermarkOutput);
+
+ int outputId = multiplexer.registerNewOutput();
+ WatermarkOutput immediateOutput = multiplexer.getImmediateOutput(outputId);
+ WatermarkOutput deferredOutput = multiplexer.getDeferredOutput(outputId);
+
+ deferredOutput.emitWatermark(new Watermark(5));
+ multiplexer.onPeriodicEmit();
+
+ assertThat(underlyingWatermarkOutput.lastWatermark(), is(watermark(5)));
+
+ immediateOutput.emitWatermark(new Watermark(2));
+
+ assertThat(underlyingWatermarkOutput.lastWatermark(), is(watermark(5)));
+
+ multiplexer.onPeriodicEmit();
+ assertThat(underlyingWatermarkOutput.lastWatermark(), is(watermark(5)));
+ }
+
+ @Test
+ public void lowerImmediateUpdateOnSameOutputDoesNotEmitCombinedUpdate() {
+ TestingWatermarkOutput underlyingWatermarkOutput = createTestingWatermarkOutput();
+ WatermarkOutputMultiplexer multiplexer =
+ new WatermarkOutputMultiplexer(underlyingWatermarkOutput);
+
+ int outputId = multiplexer.registerNewOutput();
+ WatermarkOutput immediateOutput = multiplexer.getImmediateOutput(outputId);
+ WatermarkOutput deferredOutput = multiplexer.getDeferredOutput(outputId);
+
+ deferredOutput.emitWatermark(new Watermark(5));
+ immediateOutput.emitWatermark(new Watermark(2));
+
+ assertThat(underlyingWatermarkOutput.lastWatermark(), is(nullValue()));
+ }
+
+ /**
+ * Convenience method so we don't have to go through the output ID dance when we only want an
+ * immediate output for a given output ID.
+ */
+ private static WatermarkOutput createImmediateOutput(WatermarkOutputMultiplexer multiplexer) {
+ int outputId = multiplexer.registerNewOutput();
+ return multiplexer.getImmediateOutput(outputId);
+ }
+
+ /**
+ * Convenience method so we don't have to go through the output ID dance when we only want an
+ * deferred output for a given output ID.
+ */
+ private static WatermarkOutput createDeferredOutput(WatermarkOutputMultiplexer multiplexer) {
+ int outputId = multiplexer.registerNewOutput();
+ return multiplexer.getDeferredOutput(outputId);
+ }
+
+ private static TestingWatermarkOutput createTestingWatermarkOutput() {
+ return new TestingWatermarkOutput();
+ }
+}