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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.skyframe;
import com.google.common.annotations.VisibleForTesting;
import com.google.common.collect.Sets;
import com.google.devtools.build.lib.concurrent.AbstractQueueVisitor;
import com.google.devtools.build.lib.concurrent.ErrorClassifier;
import com.google.devtools.build.lib.concurrent.ForkJoinQuiescingExecutor;
import com.google.devtools.build.lib.concurrent.QuiescingExecutor;
import com.google.devtools.build.skyframe.ParallelEvaluatorContext.RunnableMaker;
import java.util.Collection;
import java.util.Set;
import java.util.concurrent.CountDownLatch;
import java.util.concurrent.ForkJoinPool;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicBoolean;
/**
* Threadpool manager for {@link ParallelEvaluator}. Wraps a {@link QuiescingExecutor} and keeps
* track of pending nodes.
*/
class NodeEntryVisitor {
static final ErrorClassifier NODE_ENTRY_VISITOR_ERROR_CLASSIFIER =
new ErrorClassifier() {
@Override
protected ErrorClassification classifyException(Exception e) {
if (e instanceof SchedulerException) {
return ErrorClassification.CRITICAL;
}
if (e instanceof RuntimeException) {
// We treat non-SchedulerException RuntimeExceptions as more severe than
// SchedulerExceptions so that AbstractQueueVisitor will propagate instances of the
// former. They indicate actual Blaze bugs, rather than normal Skyframe evaluation
// control flow.
return ErrorClassification.CRITICAL_AND_LOG;
}
return ErrorClassification.NOT_CRITICAL;
}
};
private final QuiescingExecutor quiescingExecutor;
private final AtomicBoolean preventNewEvaluations = new AtomicBoolean(false);
private final Set<RuntimeException> crashes = Sets.newConcurrentHashSet();
private final DirtyTrackingProgressReceiver progressReceiver;
/**
* Function that allows this visitor to execute the appropriate {@link Runnable} when given a
* {@link SkyKey} to evaluate.
*/
private final RunnableMaker runnableMaker;
NodeEntryVisitor(
ForkJoinPool forkJoinPool,
DirtyTrackingProgressReceiver progressReceiver,
RunnableMaker runnableMaker) {
this.quiescingExecutor = ForkJoinQuiescingExecutor.newBuilder()
.withOwnershipOf(forkJoinPool)
.setErrorClassifier(NODE_ENTRY_VISITOR_ERROR_CLASSIFIER)
.build();
this.progressReceiver = progressReceiver;
this.runnableMaker = runnableMaker;
}
NodeEntryVisitor(
int threadCount,
DirtyTrackingProgressReceiver progressReceiver,
RunnableMaker runnableMaker) {
quiescingExecutor =
AbstractQueueVisitor.createWithPriorityQueue(
threadCount,
/*keepAliveTime=*/ 1,
TimeUnit.SECONDS,
/*failFastOnException*/ true,
"skyframe-evaluator",
NODE_ENTRY_VISITOR_ERROR_CLASSIFIER);
this.progressReceiver = progressReceiver;
this.runnableMaker = runnableMaker;
}
void waitForCompletion() throws InterruptedException {
quiescingExecutor.awaitQuiescence(/*interruptWorkers=*/ true);
}
/**
* Enqueue {@code key} for evaluation, at {@code evaluationPriority} if this visitor is using a
* priority queue.
*
* <p>{@code evaluationPriority} is used to minimize evaluation "sprawl": inefficiencies coming
* from incompletely evaluating many nodes, versus focusing on finishing the evaluation of nodes
* that have already started evaluating. Sprawl can be expensive because an incompletely evaluated
* node keeps state in Skyframe, and often in external caches, that uses memory.
*
* <p>In general, {@code evaluationPriority} should be maximal ({@link Integer#MAX_VALUE}) when
* restarting a node that has already started evaluation, and minimal when enqueueing a node that
* no other tasks depend on. Setting {@code evaluationPriority} to the same value for all children
* of a parent has good results experimentally, since it prioritizes batches of work that can be
* used together. Similarly, prioritizing deeper nodes (depth-first search of the evaluation
* graph) also has good results experimentally, since it minimizes sprawl.
*/
void enqueueEvaluation(SkyKey key, int evaluationPriority) {
if (preventNewEvaluations.get()) {
// If an error happens in nokeep_going mode, we still want to mark these nodes as inflight,
// otherwise cleanup will not happen properly.
progressReceiver.enqueueAfterError(key);
return;
}
progressReceiver.enqueueing(key);
quiescingExecutor.execute(runnableMaker.make(key, evaluationPriority));
}
/**
* Stop any new evaluations from being enqueued. Returns whether this was the first thread to
* request a halt.
*
* <p>If called from within node evaluation, the caller may use the return value to determine
* whether it is responsible for throwing an exception to halt evaluation at the executor level.
*/
boolean preventNewEvaluations() {
return preventNewEvaluations.compareAndSet(false, true);
}
void noteCrash(RuntimeException e) {
crashes.add(e);
}
Collection<RuntimeException> getCrashes() {
return crashes;
}
@VisibleForTesting
CountDownLatch getExceptionLatchForTestingOnly() {
return quiescingExecutor.getExceptionLatchForTestingOnly();
}
}
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