com.google.common.util.concurrent.AbstractTransformFuture Maven / Gradle / Ivy
Go to download
Show more of this group Show more artifacts with this name
Show all versions of guava Show documentation
Show all versions of guava Show documentation
Guava is a suite of core and expanded libraries that include
utility classes, google's collections, io classes, and much
much more.
/*
* Copyright (C) 2006 The Guava Authors
*
* 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.common.util.concurrent;
import static com.google.common.base.Preconditions.checkNotNull;
import static com.google.common.util.concurrent.Futures.getDone;
import static com.google.common.util.concurrent.MoreExecutors.rejectionPropagatingExecutor;
import static com.google.common.util.concurrent.Platform.restoreInterruptIfIsInterruptedException;
import com.google.common.annotations.GwtCompatible;
import com.google.common.base.Function;
import com.google.errorprone.annotations.ForOverride;
import com.google.errorprone.annotations.concurrent.LazyInit;
import java.util.concurrent.CancellationException;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.Executor;
import javax.annotation.CheckForNull;
import org.checkerframework.checker.nullness.qual.Nullable;
/** Implementations of {@code Futures.transform*}. */
@GwtCompatible
@ElementTypesAreNonnullByDefault
@SuppressWarnings("nullness") // TODO(b/147136275): Remove once our checker understands & and |.
abstract class AbstractTransformFuture<
I extends @Nullable Object, O extends @Nullable Object, F, T extends @Nullable Object>
extends FluentFuture.TrustedFuture implements Runnable {
static ListenableFuture create(
ListenableFuture input,
AsyncFunction function,
Executor executor) {
checkNotNull(executor);
AsyncTransformFuture output = new AsyncTransformFuture<>(input, function);
input.addListener(output, rejectionPropagatingExecutor(executor, output));
return output;
}
static ListenableFuture create(
ListenableFuture input, Function function, Executor executor) {
checkNotNull(function);
TransformFuture output = new TransformFuture<>(input, function);
input.addListener(output, rejectionPropagatingExecutor(executor, output));
return output;
}
/*
* In certain circumstances, this field might theoretically not be visible to an afterDone() call
* triggered by cancel(). For details, see the comments on the fields of TimeoutFuture.
*/
@CheckForNull @LazyInit ListenableFuture inputFuture;
@CheckForNull @LazyInit F function;
AbstractTransformFuture(ListenableFuture inputFuture, F function) {
this.inputFuture = checkNotNull(inputFuture);
this.function = checkNotNull(function);
}
@Override
@SuppressWarnings("CatchingUnchecked") // sneaky checked exception
public final void run() {
ListenableFuture localInputFuture = inputFuture;
F localFunction = function;
if (isCancelled() | localInputFuture == null | localFunction == null) {
return;
}
inputFuture = null;
if (localInputFuture.isCancelled()) {
@SuppressWarnings("unchecked")
boolean unused =
setFuture((ListenableFuture) localInputFuture); // Respects cancellation cause setting
return;
}
/*
* Any of the setException() calls below can fail if the output Future is cancelled between now
* and then. This means that we're silently swallowing an exception -- maybe even an Error. But
* this is no worse than what FutureTask does in that situation. Additionally, because the
* Future was cancelled, its listeners have been run, so its consumers will not hang.
*
* Contrast this to the situation we have if setResult() throws, a situation described below.
*/
I sourceResult;
try {
sourceResult = getDone(localInputFuture);
} catch (CancellationException e) {
// TODO(user): verify future behavior - unify logic with getFutureValue in AbstractFuture. This
// code should be unreachable with correctly implemented Futures.
// Cancel this future and return.
// At this point, inputFuture is cancelled and outputFuture doesn't exist, so the value of
// mayInterruptIfRunning is irrelevant.
cancel(false);
return;
} catch (ExecutionException e) {
// Set the cause of the exception as this future's exception.
setException(e.getCause());
return;
} catch (Exception e) { // sneaky checked exception
// Bug in inputFuture.get(). Propagate to the output Future so that its consumers don't hang.
setException(e);
return;
} catch (Error e) {
/*
* StackOverflowError, OutOfMemoryError (e.g., from allocating ExecutionException), or
* something. Try to treat it like a RuntimeException. If we overflow the stack again, the
* resulting Error will propagate upward up to the root call to set().
*/
setException(e);
return;
}
T transformResult;
try {
transformResult = doTransform(localFunction, sourceResult);
} catch (Throwable t) {
restoreInterruptIfIsInterruptedException(t);
// This exception is irrelevant in this thread, but useful for the client.
setException(t);
return;
} finally {
function = null;
}
/*
* If set()/setValue() throws an Error, we let it propagate. Why? The most likely Error is a
* StackOverflowError (from deep transform(..., directExecutor()) nesting), and calling
* setException(stackOverflowError) would fail:
*
* - If the stack overflowed before set()/setValue() could even store the result in the output
* Future, then a call setException() would likely also overflow.
*
* - If the stack overflowed after set()/setValue() stored its result, then a call to
* setException() will be a no-op because the Future is already done.
*
* Both scenarios are bad: The output Future might never complete, or, if it does complete, it
* might not run some of its listeners. The likely result is that the app will hang. (And of
* course stack overflows are bad news in general. For example, we may have overflowed in the
* middle of defining a class. If so, that class will never be loadable in this process.) The
* best we can do (since logging may overflow the stack) is to let the error propagate. Because
* it is an Error, it won't be caught and logged by AbstractFuture.executeListener. Instead, it
* can propagate through many layers of AbstractTransformFuture up to the root call to set().
*
* https://github.com/google/guava/issues/2254
*
* Other kinds of Errors are possible:
*
* - OutOfMemoryError from allocations in setFuture(): The calculus here is similar to
* StackOverflowError: We can't reliably call setException(error).
*
* - Any kind of Error from a listener. Even if we could distinguish that case (by exposing some
* extra state from AbstractFuture), our options are limited: A call to setException() would be
* a no-op. We could log, but if that's what we really want, we should modify
* AbstractFuture.executeListener to do so, since that method would have the ability to continue
* to execute other listeners.
*
* What about RuntimeException? If there is a bug in set()/setValue() that produces one, it will
* propagate, too, but only as far as AbstractFuture.executeListener, which will catch and log
* it.
*/
setResult(transformResult);
}
/** Template method for subtypes to actually run the transform. */
@ForOverride
@ParametricNullness
abstract T doTransform(F function, @ParametricNullness I result) throws Exception;
/** Template method for subtypes to actually set the result. */
@ForOverride
abstract void setResult(@ParametricNullness T result);
@Override
protected final void afterDone() {
maybePropagateCancellationTo(inputFuture);
this.inputFuture = null;
this.function = null;
}
@Override
@CheckForNull
protected String pendingToString() {
ListenableFuture localInputFuture = inputFuture;
F localFunction = function;
String superString = super.pendingToString();
String resultString = "";
if (localInputFuture != null) {
resultString = "inputFuture=[" + localInputFuture + "], ";
}
if (localFunction != null) {
return resultString + "function=[" + localFunction + "]";
} else if (superString != null) {
return resultString + superString;
}
return null;
}
/**
* An {@link AbstractTransformFuture} that delegates to an {@link AsyncFunction} and {@link
* #setFuture(ListenableFuture)}.
*/
private static final class AsyncTransformFuture<
I extends @Nullable Object, O extends @Nullable Object>
extends AbstractTransformFuture<
I, O, AsyncFunction, ListenableFuture> {
AsyncTransformFuture(
ListenableFuture inputFuture, AsyncFunction function) {
super(inputFuture, function);
}
@Override
ListenableFuture doTransform(
AsyncFunction function, @ParametricNullness I input)
throws Exception {
ListenableFuture outputFuture = function.apply(input);
checkNotNull(
outputFuture,
"AsyncFunction.apply returned null instead of a Future. "
+ "Did you mean to return immediateFuture(null)? %s",
function);
return outputFuture;
}
@Override
void setResult(ListenableFuture result) {
setFuture(result);
}
}
/**
* An {@link AbstractTransformFuture} that delegates to a {@link Function} and {@link
* #set(Object)}.
*/
private static final class TransformFuture
extends AbstractTransformFuture, O> {
TransformFuture(
ListenableFuture inputFuture, Function function) {
super(inputFuture, function);
}
@Override
@ParametricNullness
O doTransform(Function function, @ParametricNullness I input) {
return function.apply(input);
}
@Override
void setResult(@ParametricNullness O result) {
set(result);
}
}
}