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/*
* 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.runtime.taskexecutor;
import org.apache.flink.api.common.time.Time;
import org.apache.flink.runtime.concurrent.ScheduledExecutor;
import javax.annotation.Nonnegative;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import java.util.Optional;
import java.util.concurrent.CompletableFuture;
import static java.util.Objects.requireNonNull;
import static org.apache.flink.util.Preconditions.checkArgument;
import static org.apache.flink.util.Preconditions.checkNotNull;
/**
* Samples the stack traces of tasks for back pressure tracking.
*
* @see org.apache.flink.runtime.rest.handler.legacy.backpressure.BackPressureStatsTracker
*/
class StackTraceSampleService {
private final ScheduledExecutor scheduledExecutor;
StackTraceSampleService(final ScheduledExecutor scheduledExecutor) {
this.scheduledExecutor = requireNonNull(scheduledExecutor, "scheduledExecutor must not be null");
}
/**
* Returns a future that completes with a given number of stack trace samples of a task thread.
*
* @param task The task to be sampled from.
* @param numSamples The number of samples.
* @param delayBetweenSamples The time to wait between taking samples.
* @param maxStackTraceDepth The maximum depth of the returned stack traces.
* Negative means unlimited.
* @return A future containing the stack trace samples.
*/
public CompletableFuture> requestStackTraceSample(
final StackTraceSampleableTask task,
@Nonnegative final int numSamples,
final Time delayBetweenSamples,
final int maxStackTraceDepth) {
checkNotNull(task, "task must not be null");
checkArgument(numSamples > 0, "numSamples must be positive");
checkNotNull(delayBetweenSamples, "delayBetweenSamples must not be null");
return requestStackTraceSample(
task,
numSamples,
delayBetweenSamples,
maxStackTraceDepth,
new ArrayList<>(numSamples),
new CompletableFuture<>());
}
private CompletableFuture> requestStackTraceSample(
final StackTraceSampleableTask task,
final int numSamples,
final Time delayBetweenSamples,
final int maxStackTraceDepth,
final List currentTraces,
final CompletableFuture> resultFuture) {
final Optional stackTrace = getStackTrace(task, maxStackTraceDepth);
if (stackTrace.isPresent()) {
currentTraces.add(stackTrace.get());
} else if (!currentTraces.isEmpty()) {
resultFuture.complete(currentTraces);
return resultFuture;
} else {
throw new IllegalStateException(String.format("Cannot sample task %s. " +
"The task is not running.",
task.getExecutionId()));
}
if (numSamples > 1) {
scheduledExecutor.schedule(() -> requestStackTraceSample(
task,
numSamples - 1,
delayBetweenSamples,
maxStackTraceDepth,
currentTraces,
resultFuture), delayBetweenSamples.getSize(), delayBetweenSamples.getUnit());
} else {
resultFuture.complete(currentTraces);
}
return resultFuture;
}
private Optional getStackTrace(final StackTraceSampleableTask task, final int maxStackTraceDepth) {
if (!task.isRunning()) {
return Optional.empty();
}
final StackTraceElement[] stackTrace = task.getStackTrace();
return Optional.of(truncateStackTrace(stackTrace, maxStackTraceDepth));
}
private StackTraceElement[] truncateStackTrace(final StackTraceElement[] stackTrace, final int maxStackTraceDepth) {
if (maxStackTraceDepth > 0) {
return Arrays.copyOfRange(stackTrace, 0, Math.min(maxStackTraceDepth, stackTrace.length));
}
return stackTrace;
}
}
