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// Copyright 2014 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.base.Preconditions;
import javax.annotation.Nullable;
/**
* Base class of exceptions thrown by {@link SkyFunction#compute} on failure.
*
* SkyFunctions should declare a subclass {@code C} of {@link SkyFunctionException} whose
* constructors forward fine-grained exception types (e.g. {@code IOException}) to
* {@link SkyFunctionException}'s constructor, and they should also declare
* {@link SkyFunction#compute} to throw {@code C}. This way the type system checks that no
* unexpected exceptions are thrown by the {@link SkyFunction}.
*
* <p>We took this approach over using a generic exception class since Java disallows it because of
* type erasure
* (see http://docs.oracle.com/javase/tutorial/java/generics/restrictions.html#cannotCatch).
*
* <p> Note that there are restrictions on what Exception types are allowed to be wrapped in this
* manner. See {@link SkyFunctionException#validateExceptionType}.
*
* <p>Failures are explicitly either transient or persistent. The transience of the failure from
* {@link SkyFunction#compute} should be influenced only by the computations done, and not by the
* transience of the failures from computations requested via
* {@link SkyFunction.Environment#getValueOrThrow}.
*/
public abstract class SkyFunctionException extends Exception {
/** The transience of the error. */
public enum Transience {
/**
* An error that may or may not occur again if the computation were re-run. If a computation
* results in a transient error and is needed on a subsequent MemoizingEvaluator#evaluate call,
* it will be re-executed.
*/
TRANSIENT,
/**
* An error that is completely deterministic and persistent in terms of the computation's
* inputs. Persistent errors may be cached.
*/
PERSISTENT;
}
private final Transience transience;
@Nullable
private final SkyKey rootCause;
public SkyFunctionException(Exception cause, Transience transience) {
this(cause, transience, null);
}
/** Used to rethrow a child error that the parent cannot handle. */
public SkyFunctionException(Exception cause, SkyKey childKey) {
this(cause, Transience.PERSISTENT, childKey);
}
private SkyFunctionException(Exception cause, Transience transience, SkyKey rootCause) {
super(Preconditions.checkNotNull(cause));
SkyFunctionException.validateExceptionType(cause.getClass());
this.transience = transience;
this.rootCause = rootCause;
}
@Nullable
public final SkyKey getRootCauseSkyKey() {
return rootCause;
}
public final boolean isTransient() {
return transience == Transience.TRANSIENT;
}
/**
* Catastrophic failures halt the build even when in keepGoing mode.
*/
public boolean isCatastrophic() {
return false;
}
@Override
public synchronized Exception getCause() {
return (Exception) super.getCause();
}
static <E extends Exception> void validateExceptionType(Class<E> exceptionClass) {
if (exceptionClass.isAssignableFrom(RuntimeException.class)) {
throw new IllegalStateException(exceptionClass.getSimpleName() + " is a supertype of "
+ "RuntimeException. Don't do this since then you would potentially swallow all "
+ "RuntimeExceptions, even those from Skyframe");
}
if (RuntimeException.class.isAssignableFrom(exceptionClass)) {
throw new IllegalStateException(exceptionClass.getSimpleName() + " is a subtype of "
+ "RuntimeException. You should rewrite your code to use checked exceptions.");
}
if (InterruptedException.class.isAssignableFrom(exceptionClass)) {
throw new IllegalStateException(exceptionClass.getSimpleName() + " is a subtype of "
+ "InterruptedException. Don't do this; Skyframe handles interrupts separately from the "
+ "general SkyFunctionException mechanism.");
}
}
/** A {@link SkyFunctionException} with a definite root cause. */
public static class ReifiedSkyFunctionException extends SkyFunctionException {
private final boolean isCatastrophic;
public ReifiedSkyFunctionException(SkyFunctionException e, SkyKey key) {
this(e.getCause(), e.transience, key, e.getRootCauseSkyKey(), e.isCatastrophic());
}
protected ReifiedSkyFunctionException(
Exception cause,
Transience transience,
SkyKey key,
@Nullable SkyKey rootCauseSkyKey,
boolean isCatastrophic) {
super(cause, transience, rootCauseSkyKey == null ? key : rootCauseSkyKey);
this.isCatastrophic = isCatastrophic;
}
@Override
public boolean isCatastrophic() {
return isCatastrophic;
}
}
}
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