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// Copyright 2016 The Bazel Authors. All rights reserved.
//
// 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 com.google.devtools.build.lib.query2.engine;
import com.google.devtools.build.lib.concurrent.MoreFutures;
import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.ForkJoinPool;
import java.util.concurrent.ForkJoinTask;
/** Several utilities to aid in writing {@link QueryExpression#parEval} implementations. */
public class ParallelQueryUtils {
/**
* Encapsulation of a subtask of parallel evaluation of a {@link QueryExpression}. See
* {@link #executeQueryTasksAndWaitInterruptibly}.
*/
public interface QueryTask {
void execute() throws QueryException, InterruptedException;
}
/**
* Executes the given {@link QueryTask}s using the given {@link ForkJoinPool} and interruptibly
* waits for their completion. Throws the first {@link QueryException} or
* {@link InterruptedException} encountered during parallel execution.
*/
public static void executeQueryTasksAndWaitInterruptibly(
List<QueryTask> queryTasks,
ForkJoinPool forkJoinPool) throws QueryException, InterruptedException {
ArrayList<QueryTaskForkJoinTask> forkJoinTasks = new ArrayList<>(queryTasks.size());
for (QueryTask queryTask : queryTasks) {
QueryTaskForkJoinTask forkJoinTask = adaptAsForkJoinTask(queryTask);
forkJoinTasks.add(forkJoinTask);
forkJoinPool.submit(forkJoinTask);
}
try {
MoreFutures.waitForAllInterruptiblyFailFast(forkJoinTasks);
} catch (ExecutionException e) {
throw rethrowCause(e);
}
}
private static QueryTaskForkJoinTask adaptAsForkJoinTask(QueryTask queryTask) {
return new QueryTaskForkJoinTask(queryTask);
}
private static RuntimeException rethrowCause(ExecutionException e)
throws QueryException, InterruptedException {
Throwable cause = e.getCause();
if (cause instanceof ParallelRuntimeException) {
((ParallelRuntimeException) cause).rethrow();
}
throw new IllegalStateException(e);
}
// ForkJoinTask#adapt(Callable) wraps thrown checked exceptions as RuntimeExceptions. We avoid
// having to think about that messiness (which is inconsistent with other Future implementations)
// by having our own ForkJoinTask subclass and managing checked exceptions ourselves.
private static class QueryTaskForkJoinTask extends ForkJoinTask<Void> {
private final QueryTask queryTask;
private QueryTaskForkJoinTask(QueryTask queryTask) {
this.queryTask = queryTask;
}
@Override
public Void getRawResult() {
return null;
}
@Override
protected void setRawResult(Void value) {
}
@Override
protected boolean exec() {
try {
queryTask.execute();
} catch (QueryException queryException) {
throw new ParallelRuntimeQueryException(queryException);
} catch (InterruptedException interruptedException) {
throw new ParallelInterruptedQueryException(interruptedException);
}
return true;
}
}
private abstract static class ParallelRuntimeException extends RuntimeException {
abstract void rethrow() throws QueryException, InterruptedException;
}
private static class ParallelRuntimeQueryException extends ParallelRuntimeException {
private final QueryException queryException;
private ParallelRuntimeQueryException(QueryException queryException) {
this.queryException = queryException;
}
@Override
void rethrow() throws QueryException, InterruptedException {
throw queryException;
}
}
private static class ParallelInterruptedQueryException extends ParallelRuntimeException {
private final InterruptedException interruptedException;
private ParallelInterruptedQueryException(InterruptedException interruptedException) {
this.interruptedException = interruptedException;
}
@Override
void rethrow() throws QueryException, InterruptedException {
throw interruptedException;
}
}
}
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