/*
* Original Guava code is copyright (C) 2015 The Guava Authors.
* Modifications from Guava are copyright (C) 2016 DiffPlug.
*
* 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.diffplug.common.util.concurrent;
import static com.diffplug.common.base.Preconditions.checkNotNull;
import static com.diffplug.common.util.concurrent.MoreExecutors.directExecutor;
import static com.diffplug.common.util.concurrent.Platform.isInstanceOfThrowableClass;
import static com.diffplug.common.util.concurrent.Uninterruptibles.getUninterruptibly;
import java.lang.reflect.UndeclaredThrowableException;
import java.util.Collections;
import java.util.List;
import java.util.Optional;
import java.util.concurrent.CancellationException;
import java.util.concurrent.ConcurrentLinkedQueue;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.Executor;
import java.util.concurrent.Future;
import java.util.concurrent.RejectedExecutionException;
import java.util.concurrent.ScheduledExecutorService;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.TimeoutException;
import java.util.function.Function;
import java.util.logging.Level;
import java.util.logging.Logger;
import javax.annotation.CheckReturnValue;
import javax.annotation.Nullable;
import com.diffplug.common.annotations.Beta;
import com.diffplug.common.annotations.GwtCompatible;
import com.diffplug.common.annotations.GwtIncompatible;
import com.diffplug.common.base.Preconditions;
import com.diffplug.common.collect.ImmutableCollection;
import com.diffplug.common.collect.ImmutableList;
import com.diffplug.common.collect.Lists;
import com.diffplug.common.collect.Queues;
/**
* Static utility methods pertaining to the {@link Future} interface.
*
* Many of these methods use the {@link ListenableFuture} API; consult the
* Guava User Guide article on
* {@code ListenableFuture} .
*
* @author Kevin Bourrillion
* @author Nishant Thakkar
* @author Sven Mawson
* @since 1.0
*/
@Beta
@GwtCompatible(emulated = true)
public final class Futures extends GwtFuturesCatchingSpecialization {
// A note on memory visibility.
// Many of the utilities in this class (transform, withFallback, withTimeout, asList, combine)
// have two requirements that significantly complicate their design.
// 1. Cancellation should propagate from the returned future to the input future(s).
// 2. The returned futures shouldn't unnecessarily 'pin' their inputs after completion.
//
// A consequence of these requirements is that the delegate futures cannot be stored in
// final fields.
//
// For simplicity the rest of this description will discuss Futures.catching since it is the
// simplest instance, though very similar descriptions apply to many other classes in this file.
//
// In the constructor of AbstractCatchingFuture, the delegate future is assigned to a field
// 'inputFuture'. That field is non-final and non-volatile. There are 2 places where the
// 'inputFuture' field is read and where we will have to consider visibility of the write
// operation in the constructor.
//
// 1. In the listener that performs the callback. In this case it is fine since inputFuture is
// assigned prior to calling addListener, and addListener happens-before any invocation of the
// listener. Notably, this means that 'volatile' is unnecessary to make 'inputFuture' visible
// to the listener.
//
// 2. In done() where we may propagate cancellation to the input. In this case it is _not_ fine.
// There is currently nothing that enforces that the write to inputFuture in the constructor is
// visible to done(). This is because there is no happens before edge between the write and a
// (hypothetical) unsafe read by our caller. Note: adding 'volatile' does not fix this issue,
// it would just add an edge such that if done() observed non-null, then it would also
// definitely observe all earlier writes, but we still have no guarantee that done() would see
// the inital write (just stronger guarantees if it does).
//
// See: http://cs.oswego.edu/pipermail/concurrency-interest/2015-January/013800.html
// For a (long) discussion about this specific issue and the general futility of life.
//
// For the time being we are OK with the problem discussed above since it requires a caller to
// introduce a very specific kind of data-race. And given the other operations performed by these
// methods that involve volatile read/write operations, in practice there is no issue. Also, the
// way in such a visibility issue would surface is most likely as a failure of cancel() to
// propagate to the input. Cancellation propagation is fundamentally racy so this is fine.
//
// Future versions of the JMM may revise safe construction semantics in such a way that we can
// safely publish these objects and we won't need this whole discussion.
// TODO(user,lukes): consider adding volatile to all these fields since in current known JVMs
// that should resolve the issue. This comes at the cost of adding more write barriers to the
// implementations.
private Futures() {}
/**
* Creates a {@link CheckedFuture} out of a normal {@link ListenableFuture} and a {@link Function}
* that maps from {@link Exception} instances into the appropriate checked type.
*
*
Warning: We recommend against using {@code CheckedFuture} in new projects. {@code
* CheckedFuture} is difficult to build libraries atop. {@code CheckedFuture} ports of methods
* like {@link Futures#transformAsync} have historically had bugs, and some of these bugs are
* necessary, unavoidable consequences of the {@code CheckedFuture} API. Additionally, {@code
* CheckedFuture} encourages users to take exceptions from one thread and rethrow them in another,
* producing confusing stack traces.
*
*
The given mapping function will be applied to an
* {@link InterruptedException}, a {@link CancellationException}, or an
* {@link ExecutionException}.
* See {@link Future#get()} for details on the exceptions thrown.
*
* @since 9.0 (source-compatible since 1.0)
*/
@GwtIncompatible("TODO")
@CheckReturnValue
public static CheckedFuture makeChecked(
ListenableFuture future, Function mapper) {
return new MappingCheckedFuture(checkNotNull(future), mapper);
}
private abstract static class ImmediateFuture
implements ListenableFuture {
private static final Logger log = Logger.getLogger(ImmediateFuture.class.getName());
@Override
public void addListener(Runnable listener, Executor executor) {
checkNotNull(listener, "Runnable was null.");
checkNotNull(executor, "Executor was null.");
try {
executor.execute(listener);
} catch (RuntimeException e) {
// ListenableFuture's contract is that it will not throw unchecked
// exceptions, so log the bad runnable and/or executor and swallow it.
log.log(Level.SEVERE, "RuntimeException while executing runnable "
+ listener + " with executor " + executor, e);
}
}
@Override
public boolean cancel(boolean mayInterruptIfRunning) {
return false;
}
@Override
public abstract V get() throws ExecutionException;
@Override
public V get(long timeout, TimeUnit unit) throws ExecutionException {
checkNotNull(unit);
return get();
}
@Override
public boolean isCancelled() {
return false;
}
@Override
public boolean isDone() {
return true;
}
}
private static class ImmediateSuccessfulFuture extends ImmediateFuture {
static final ImmediateSuccessfulFuture NULL = new ImmediateSuccessfulFuture(null);
@Nullable
private final V value;
ImmediateSuccessfulFuture(@Nullable V value) {
this.value = value;
}
@Override
public V get() {
return value;
}
}
@GwtIncompatible("TODO")
private static class ImmediateSuccessfulCheckedFuture
extends ImmediateFutureimplements CheckedFuture {
@Nullable
private final V value;
ImmediateSuccessfulCheckedFuture(@Nullable V value) {
this.value = value;
}
@Override
public V get() {
return value;
}
@Override
public V checkedGet() {
return value;
}
@Override
public V checkedGet(long timeout, TimeUnit unit) {
checkNotNull(unit);
return value;
}
}
private static class ImmediateFailedFuture extends ImmediateFuture {
private final Throwable thrown;
ImmediateFailedFuture(Throwable thrown) {
this.thrown = thrown;
}
@Override
public V get() throws ExecutionException {
throw new ExecutionException(thrown);
}
}
@GwtIncompatible("TODO")
private static class ImmediateCancelledFuture extends ImmediateFuture {
private final CancellationException thrown;
ImmediateCancelledFuture() {
this.thrown = new CancellationException("Immediate cancelled future.");
}
@Override
public boolean isCancelled() {
return true;
}
@Override
public V get() {
throw AbstractFuture.cancellationExceptionWithCause(
"Task was cancelled.", thrown);
}
}
@GwtIncompatible("TODO")
private static class ImmediateFailedCheckedFuture
extends ImmediateFutureimplements CheckedFuture {
private final X thrown;
ImmediateFailedCheckedFuture(X thrown) {
this.thrown = thrown;
}
@Override
public V get() throws ExecutionException {
throw new ExecutionException(thrown);
}
@Override
public V checkedGet() throws X {
throw thrown;
}
@Override
public V checkedGet(long timeout, TimeUnit unit) throws X {
checkNotNull(unit);
throw thrown;
}
}
/**
* Creates a {@code ListenableFuture} which has its value set immediately upon
* construction. The getters just return the value. This {@code Future} can't
* be canceled or timed out and its {@code isDone()} method always returns
* {@code true}.
*/
@CheckReturnValue
public static ListenableFuture immediateFuture(@Nullable V value) {
if (value == null) {
// This cast is safe because null is assignable to V for all V (i.e. it is covariant)
@SuppressWarnings({"unchecked", "rawtypes"})
ListenableFuture typedNull = (ListenableFuture) ImmediateSuccessfulFuture.NULL;
return typedNull;
}
return new ImmediateSuccessfulFuture(value);
}
/**
* Returns a {@code CheckedFuture} which has its value set immediately upon
* construction.
*
* The returned {@code Future} can't be cancelled, and its {@code isDone()}
* method always returns {@code true}. Calling {@code get()} or {@code
* checkedGet()} will immediately return the provided value.
*/
@GwtIncompatible("TODO")
@CheckReturnValue
public static CheckedFuture immediateCheckedFuture(@Nullable V value) {
return new ImmediateSuccessfulCheckedFuture(value);
}
/**
* Returns a {@code ListenableFuture} which has an exception set immediately
* upon construction.
*
* The returned {@code Future} can't be cancelled, and its {@code isDone()}
* method always returns {@code true}. Calling {@code get()} will immediately
* throw the provided {@code Throwable} wrapped in an {@code
* ExecutionException}.
*/
@CheckReturnValue
public static ListenableFuture immediateFailedFuture(
Throwable throwable) {
checkNotNull(throwable);
return new ImmediateFailedFuture(throwable);
}
/**
* Creates a {@code ListenableFuture} which is cancelled immediately upon
* construction, so that {@code isCancelled()} always returns {@code true}.
*
* @since 14.0
*/
@GwtIncompatible("TODO")
@CheckReturnValue
public static ListenableFuture immediateCancelledFuture() {
return new ImmediateCancelledFuture();
}
/**
* Returns a {@code CheckedFuture} which has an exception set immediately upon
* construction.
*
* The returned {@code Future} can't be cancelled, and its {@code isDone()}
* method always returns {@code true}. Calling {@code get()} will immediately
* throw the provided {@code Exception} wrapped in an {@code
* ExecutionException}, and calling {@code checkedGet()} will throw the
* provided exception itself.
*/
@GwtIncompatible("TODO")
@CheckReturnValue
public static CheckedFuture immediateFailedCheckedFuture(X exception) {
checkNotNull(exception);
return new ImmediateFailedCheckedFuture(exception);
}
/**
* Returns a {@code Future} whose result is taken from the given primary {@code input} or, if the
* primary input fails with the given {@code exceptionType}, from the result provided by the
* {@code fallback}. {@link Function#apply} is not invoked until the primary input has failed, so
* if the primary input succeeds, it is never invoked. If, during the invocation of {@code
* fallback}, an exception is thrown, this exception is used as the result of the output {@code
* Future}.
*
* Usage example:
*
*
{@code
* ListenableFuture fetchCounterFuture = ...;
*
* // Falling back to a zero counter in case an exception happens when
* // processing the RPC to fetch counters.
* ListenableFuture faultTolerantFuture = Futures.catching(
* fetchCounterFuture, FetchException.class,
* new Function() {
* public Integer apply(FetchException e) {
* return 0;
* }
* });}
*
* This overload, which does not accept an executor, uses {@code directExecutor}, a dangerous
* choice in some cases. See the discussion in the {@link ListenableFuture#addListener
* ListenableFuture.addListener} documentation. The documentation's warnings about "lightweight
* listeners" refer here to the work done during {@code Function.apply}.
*
* @param input the primary input {@code Future}
* @param exceptionType the exception type that triggers use of {@code fallback}. To avoid hiding
* bugs and other unrecoverable errors, callers should prefer more specific types, avoiding
* {@code Throwable.class} in particular.
* @param fallback the {@link Function} implementation to be called if {@code input} fails with
* the expected exception type
* @since 19.0
*/
@GwtIncompatible("AVAILABLE but requires exceptionType to be Throwable.class")
@CheckReturnValue
public static ListenableFuture catching(
ListenableFuture input, Class exceptionType,
Function fallback) {
CatchingFuture future = new CatchingFuture(input, exceptionType, fallback);
input.addListener(future, directExecutor());
return future;
}
/**
* Returns a {@code Future} whose result is taken from the given primary {@code input} or, if the
* primary input fails with the given {@code exceptionType}, from the result provided by the
* {@code fallback}. {@link Function#apply} is not invoked until the primary input has failed, so
* if the primary input succeeds, it is never invoked. If, during the invocation of {@code
* fallback}, an exception is thrown, this exception is used as the result of the output {@code
* Future}.
*
* Usage example:
*
*
{@code
* ListenableFuture fetchCounterFuture = ...;
*
* // Falling back to a zero counter in case an exception happens when
* // processing the RPC to fetch counters.
* ListenableFuture faultTolerantFuture = Futures.catching(
* fetchCounterFuture, FetchException.class,
* new Function() {
* public Integer apply(FetchException e) {
* return 0;
* }
* }, directExecutor());}
*
* When selecting an executor, note that {@code directExecutor} is dangerous in some cases. See
* the discussion in the {@link ListenableFuture#addListener ListenableFuture.addListener}
* documentation. The documentation's warnings about "lightweight listeners" refer here to the
* work done during {@code Function.apply}.
*
* @param input the primary input {@code Future}
* @param exceptionType the exception type that triggers use of {@code fallback}. To avoid hiding
* bugs and other unrecoverable errors, callers should prefer more specific types, avoiding
* {@code Throwable.class} in particular.
* @param fallback the {@link Function} implementation to be called if {@code input} fails with
* the expected exception type
* @param executor the executor that runs {@code fallback} if {@code input} fails
* @since 19.0
*/
@GwtIncompatible("AVAILABLE but requires exceptionType to be Throwable.class")
@CheckReturnValue
public static ListenableFuture catching(
ListenableFuture input, Class exceptionType,
Function fallback, Executor executor) {
CatchingFuture future = new CatchingFuture(input, exceptionType, fallback);
input.addListener(future, rejectionPropagatingExecutor(executor, future));
return future;
}
/**
* Returns a {@code Future} whose result is taken from the given primary {@code input} or, if the
* primary input fails with the given {@code exceptionType}, from the result provided by the
* {@code fallback}. {@link AsyncFunction#apply} is not invoked until the primary input has
* failed, so if the primary input succeeds, it is never invoked. If, during the invocation of
* {@code fallback}, an exception is thrown, this exception is used as the result of the output
* {@code Future}.
*
* Usage examples:
*
*
{@code
* ListenableFuture fetchCounterFuture = ...;
*
* // Falling back to a zero counter in case an exception happens when
* // processing the RPC to fetch counters.
* ListenableFuture faultTolerantFuture = Futures.catchingAsync(
* fetchCounterFuture, FetchException.class,
* new AsyncFunction() {
* public ListenableFuture apply(FetchException e) {
* return immediateFuture(0);
* }
* });}
*
* The fallback can also choose to propagate the original exception when desired:
*
*
{@code
* ListenableFuture fetchCounterFuture = ...;
*
* // Falling back to a zero counter only in case the exception was a
* // TimeoutException.
* ListenableFuture faultTolerantFuture = Futures.catchingAsync(
* fetchCounterFuture, FetchException.class,
* new AsyncFunction() {
* public ListenableFuture apply(FetchException e)
* throws FetchException {
* if (omitDataOnFetchFailure) {
* return immediateFuture(0);
* }
* throw e;
* }
* });}
*
* This overload, which does not accept an executor, uses {@code directExecutor}, a dangerous
* choice in some cases. See the discussion in the {@link ListenableFuture#addListener
* ListenableFuture.addListener} documentation. The documentation's warnings about "lightweight
* listeners" refer here to the work done during {@code AsyncFunction.apply}, not to any work done
* to complete the returned {@code Future}.
*
* @param input the primary input {@code Future}
* @param exceptionType the exception type that triggers use of {@code fallback}. To avoid hiding
* bugs and other unrecoverable errors, callers should prefer more specific types, avoiding
* {@code Throwable.class} in particular.
* @param fallback the {@link AsyncFunction} implementation to be called if {@code input} fails
* with the expected exception type
* @since 19.0 (similar functionality in 14.0 as {@code withFallback})
*/
@GwtIncompatible("AVAILABLE but requires exceptionType to be Throwable.class")
// TODO(kak): @CheckReturnValue
public static ListenableFuture catchingAsync(
ListenableFuture input, Class exceptionType,
AsyncFunction fallback) {
AsyncCatchingFuture future = new AsyncCatchingFuture(input, exceptionType, fallback);
input.addListener(future, directExecutor());
return future;
}
/**
* Returns a {@code Future} whose result is taken from the given primary {@code input} or, if the
* primary input fails with the given {@code exceptionType}, from the result provided by the
* {@code fallback}. {@link AsyncFunction#apply} is not invoked until the primary input has
* failed, so if the primary input succeeds, it is never invoked. If, during the invocation of
* {@code fallback}, an exception is thrown, this exception is used as the result of the output
* {@code Future}.
*
* Usage examples:
*
*
{@code
* ListenableFuture fetchCounterFuture = ...;
*
* // Falling back to a zero counter in case an exception happens when
* // processing the RPC to fetch counters.
* ListenableFuture faultTolerantFuture = Futures.catchingAsync(
* fetchCounterFuture, FetchException.class,
* new AsyncFunction() {
* public ListenableFuture apply(FetchException e) {
* return immediateFuture(0);
* }
* }, directExecutor());}
*
* The fallback can also choose to propagate the original exception when desired:
*
*
{@code
* ListenableFuture fetchCounterFuture = ...;
*
* // Falling back to a zero counter only in case the exception was a
* // TimeoutException.
* ListenableFuture faultTolerantFuture = Futures.catchingAsync(
* fetchCounterFuture, FetchException.class,
* new AsyncFunction() {
* public ListenableFuture apply(FetchException e)
* throws FetchException {
* if (omitDataOnFetchFailure) {
* return immediateFuture(0);
* }
* throw e;
* }
* }, directExecutor());}
*
* When selecting an executor, note that {@code directExecutor} is dangerous in some cases. See
* the discussion in the {@link ListenableFuture#addListener ListenableFuture.addListener}
* documentation. The documentation's warnings about "lightweight listeners" refer here to the
* work done during {@code AsyncFunction.apply}, not to any work done to complete the returned
* {@code Future}.
*
* @param input the primary input {@code Future}
* @param exceptionType the exception type that triggers use of {@code fallback}. To avoid hiding
* bugs and other unrecoverable errors, callers should prefer more specific types, avoiding
* {@code Throwable.class} in particular.
* @param fallback the {@link AsyncFunction} implementation to be called if {@code input} fails
* with the expected exception type
* @param executor the executor that runs {@code fallback} if {@code input} fails
* @since 19.0 (similar functionality in 14.0 as {@code withFallback})
*/
@GwtIncompatible("AVAILABLE but requires exceptionType to be Throwable.class")
// TODO(kak): @CheckReturnValue
public static ListenableFuture catchingAsync(
ListenableFuture input, Class exceptionType,
AsyncFunction fallback, Executor executor) {
AsyncCatchingFuture future = new AsyncCatchingFuture(input, exceptionType, fallback);
input.addListener(future, rejectionPropagatingExecutor(executor, future));
return future;
}
private abstract static class AbstractCatchingFuture
extends AbstractFuture.TrustedFutureimplements Runnable {
@Nullable
ListenableFuture inputFuture;
@Nullable
Class exceptionType;
@Nullable
F fallback;
AbstractCatchingFuture(
ListenableFuture inputFuture, Class exceptionType, F fallback) {
this.inputFuture = checkNotNull(inputFuture);
this.exceptionType = checkNotNull(exceptionType);
this.fallback = checkNotNull(fallback);
}
@Override
public final void run() {
ListenableFuture localInputFuture = inputFuture;
Class localExceptionType = exceptionType;
F localFallback = fallback;
if (localInputFuture == null | localExceptionType == null | localFallback == null
| isCancelled()) {
return;
}
inputFuture = null;
exceptionType = null;
fallback = null;
Throwable throwable;
try {
set(getUninterruptibly(localInputFuture));
return;
} catch (ExecutionException e) {
throwable = e.getCause();
} catch (Throwable e) { // this includes cancellation exception
throwable = e;
}
try {
if (isInstanceOfThrowableClass(throwable, localExceptionType)) {
@SuppressWarnings("unchecked") // verified safe by isInstance
X castThrowable = (X) throwable;
doFallback(localFallback, castThrowable);
} else {
setException(throwable);
}
} catch (Throwable e) {
setException(e);
}
}
/** Template method for subtypes to actually run the fallback. */
abstract void doFallback(F fallback, X throwable) throws Exception;
@Override
final void done() {
maybePropagateCancellation(inputFuture);
this.inputFuture = null;
this.exceptionType = null;
this.fallback = null;
}
}
/**
* A {@link AbstractCatchingFuture} that delegates to an {@link AsyncFunction}
* and {@link #setFuture(ListenableFuture)} to implement {@link #doFallback}
*/
static final class AsyncCatchingFuture
extends AbstractCatchingFuture> {
AsyncCatchingFuture(ListenableFuture input, Class exceptionType,
AsyncFunction fallback) {
super(input, exceptionType, fallback);
}
@Override
void doFallback(
AsyncFunction fallback, X cause) throws Exception {
ListenableFuture replacement = fallback.apply(cause);
checkNotNull(replacement, "AsyncFunction.apply returned null instead of a Future. "
+ "Did you mean to return immediateFuture(null)?");
setFuture(replacement);
}
}
/**
* A {@link AbstractCatchingFuture} that delegates to a {@link Function}
* and {@link #set(Object)} to implement {@link #doFallback}
*/
static final class CatchingFuture
extends AbstractCatchingFuture> {
CatchingFuture(ListenableFuture input, Class exceptionType,
Function fallback) {
super(input, exceptionType, fallback);
}
@Override
void doFallback(Function fallback, X cause) throws Exception {
V replacement = fallback.apply(cause);
set(replacement);
}
}
/**
* Returns a future that delegates to another but will finish early (via a
* {@link TimeoutException} wrapped in an {@link ExecutionException}) if the
* specified duration expires.
*
* The delegate future is interrupted and cancelled if it times out.
*
* @param delegate The future to delegate to.
* @param time when to timeout the future
* @param unit the time unit of the time parameter
* @param scheduledExecutor The executor service to enforce the timeout.
*
* @since 19.0
*/
@GwtIncompatible("java.util.concurrent.ScheduledExecutorService")
@CheckReturnValue
public static ListenableFuture withTimeout(ListenableFuture delegate,
long time, TimeUnit unit, ScheduledExecutorService scheduledExecutor) {
TimeoutFuture result = new TimeoutFuture(delegate);
TimeoutFuture.Fire fire = new TimeoutFuture.Fire(result);
result.timer = scheduledExecutor.schedule(fire, time, unit);
delegate.addListener(fire, directExecutor());
return result;
}
/**
* Future that delegates to another but will finish early (via a {@link
* TimeoutException} wrapped in an {@link ExecutionException}) if the
* specified duration expires.
* The delegate future is interrupted and cancelled if it times out.
*/
private static final class TimeoutFuture extends AbstractFuture.TrustedFuture {
// Memory visibility of these fields.
// There are two cases to consider.
// 1. visibility of the writes to these fields to Fire.run
// The initial write to delegateRef is made definitely visible via the semantics of
// addListener/SES.schedule. The later racy write in cancel() is not guaranteed to be
// observed, however that is fine since the correctness is based on the atomic state in
// our base class.
// The initial write to timer is never definitely visible to Fire.run since it is assigned
// after SES.schedule is called. Therefore Fire.run has to check for null. However, it
// should be visible if Fire.run is called by delegate.addListener since addListener is
// called after the assignment to timer, and importantly this is the main situation in which
// we need to be able to see the write.
// 2. visibility of the writes to cancel
// Since these fields are non-final that means that TimeoutFuture is not being 'safely
// published', thus a motivated caller may be able to expose the reference to another thread
// that would then call cancel() and be unable to cancel the delegate.
// There are a number of ways to solve this, none of which are very pretty, and it is
// currently believed to be a purely theoretical problem (since the other actions should
// supply sufficient write-barriers).
@Nullable
ListenableFuture delegateRef;
@Nullable
Future timer;
TimeoutFuture(ListenableFuture delegate) {
this.delegateRef = Preconditions.checkNotNull(delegate);
}
/** A runnable that is called when the delegate or the timer completes. */
private static final class Fire implements Runnable {
@Nullable
TimeoutFuture timeoutFutureRef;
Fire(TimeoutFuture timeoutFuture) {
this.timeoutFutureRef = timeoutFuture;
}
@Override
public void run() {
// If either of these reads return null then we must be after a successful cancel
// or another call to this method.
TimeoutFuture timeoutFuture = timeoutFutureRef;
if (timeoutFuture == null) {
return;
}
ListenableFuture delegate = timeoutFuture.delegateRef;
if (delegate == null) {
return;
}
/*
* If we're about to complete the TimeoutFuture, we want to release our reference to it.
* Otherwise, we'll pin it (and its result) in memory until the timeout task is GCed. (The
* need to clear our reference to the TimeoutFuture is the reason we use a *static* nested
* class with a manual reference back to the "containing" class.)
*
* This has the nice-ish side effect of limiting reentrancy: run() calls
* timeoutFuture.setException() calls run(). That reentrancy would already be harmless,
* since timeoutFuture can be set (and delegate cancelled) only once. (And "set only once"
* is important for other reasons: run() can still be invoked concurrently in different
* threads, even with the above null checks.)
*/
timeoutFutureRef = null;
if (delegate.isDone()) {
timeoutFuture.setFuture(delegate);
} else {
try {
// TODO(lukes): this stack trace is particularly useless (all it does is point at the
// scheduledexecutorservice thread), consider eliminating it altogether?
timeoutFuture.setException(new TimeoutException("Future timed out: " + delegate));
} finally {
delegate.cancel(true);
}
}
}
}
@Override
void done() {
maybePropagateCancellation(delegateRef);
Future localTimer = timer;
// Try to cancel the timer as an optimization
// timer may be null if this call to run was by the timer task since there is no
// happens-before edge between the assignment to timer and an execution of the timer task.
if (localTimer != null) {
localTimer.cancel(false);
}
delegateRef = null;
timer = null;
}
}
/**
* Returns a new {@code ListenableFuture} whose result is asynchronously derived from the result
* of the given {@code Future}. More precisely, the returned {@code Future} takes its result from
* a {@code Future} produced by applying the given {@code AsyncFunction} to the result of the
* original {@code Future}. Example:
*
* {@code
* ListenableFuture rowKeyFuture = indexService.lookUp(query);
* AsyncFunction queryFunction =
* new AsyncFunction() {
* public ListenableFuture apply(RowKey rowKey) {
* return dataService.read(rowKey);
* }
* };
* ListenableFuture queryFuture =
* transformAsync(rowKeyFuture, queryFunction);}
*
* This overload, which does not accept an executor, uses {@code directExecutor}, a dangerous
* choice in some cases. See the discussion in the {@link ListenableFuture#addListener
* ListenableFuture.addListener} documentation. The documentation's warnings about "lightweight
* listeners" refer here to the work done during {@code AsyncFunction.apply}, not to any work done
* to complete the returned {@code Future}.
*
*
The returned {@code Future} attempts to keep its cancellation state in sync with that of the
* input future and that of the future returned by the function. That is, if the returned {@code
* Future} is cancelled, it will attempt to cancel the other two, and if either of the other two
* is cancelled, the returned {@code Future} will receive a callback in which it will attempt to
* cancel itself.
*
* @param input The future to transform
* @param function A function to transform the result of the input future to the result of the
* output future
* @return A future that holds result of the function (if the input succeeded) or the original
* input's failure (if not)
* @since 19.0 (in 11.0 as {@code transform})
*/
public static ListenableFuture transformAsync(
ListenableFuture input, AsyncFunction function) {
AsyncChainingFuture output = new AsyncChainingFuture(input, function);
input.addListener(output, directExecutor());
return output;
}
/**
* Returns a new {@code ListenableFuture} whose result is asynchronously derived from the result
* of the given {@code Future}. More precisely, the returned {@code Future} takes its result from
* a {@code Future} produced by applying the given {@code AsyncFunction} to the result of the
* original {@code Future}. Example:
*
* {@code
* ListenableFuture rowKeyFuture = indexService.lookUp(query);
* AsyncFunction queryFunction =
* new AsyncFunction() {
* public ListenableFuture apply(RowKey rowKey) {
* return dataService.read(rowKey);
* }
* };
* ListenableFuture queryFuture =
* transformAsync(rowKeyFuture, queryFunction, executor);}
*
* When selecting an executor, note that {@code directExecutor} is dangerous in some cases. See
* the discussion in the {@link ListenableFuture#addListener ListenableFuture.addListener}
* documentation. The documentation's warnings about "lightweight listeners" refer here to the
* work done during {@code AsyncFunction.apply}, not to any work done to complete the returned
* {@code Future}.
*
*
The returned {@code Future} attempts to keep its cancellation state in sync with that of the
* input future and that of the future returned by the chain function. That is, if the returned
* {@code Future} is cancelled, it will attempt to cancel the other two, and if either of the
* other two is cancelled, the returned {@code Future} will receive a callback in which it will
* attempt to cancel itself.
*
* @param input The future to transform
* @param function A function to transform the result of the input future to the result of the
* output future
* @param executor Executor to run the function in.
* @return A future that holds result of the function (if the input succeeded) or the original
* input's failure (if not)
* @since 19.0 (in 11.0 as {@code transform})
*/
public static ListenableFuture transformAsync(ListenableFuture input,
AsyncFunction function, Executor executor) {
checkNotNull(executor);
AsyncChainingFuture output = new AsyncChainingFuture(input, function);
input.addListener(output, rejectionPropagatingExecutor(executor, output));
return output;
}
/**
* Returns an Executor that will propagate {@link RejectedExecutionException} from the delegate
* executor to the given {@code future}.
*
* Note, the returned executor can only be used once.
*/
private static Executor rejectionPropagatingExecutor(
final Executor delegate, final AbstractFuture future) {
checkNotNull(delegate);
if (delegate == directExecutor()) {
// directExecutor() cannot throw RejectedExecutionException
return delegate;
}
return new Executor() {
volatile boolean thrownFromDelegate = true;
@Override
public void execute(final Runnable command) {
try {
delegate.execute(new Runnable() {
@Override
public void run() {
thrownFromDelegate = false;
command.run();
}
});
} catch (RejectedExecutionException e) {
if (thrownFromDelegate) {
// wrap exception?
future.setException(e);
}
// otherwise it must have been thrown from a transitive call and the delegate runnable
// should have handled it.
}
}
};
}
/**
* Returns a new {@code ListenableFuture} whose result is the product of
* applying the given {@code Function} to the result of the given {@code
* Future}. Example:
*
*
{@code
* ListenableFuture queryFuture = ...;
* Function> rowsFunction =
* new Function>() {
* public List apply(QueryResult queryResult) {
* return queryResult.getRows();
* }
* };
* ListenableFuture> rowsFuture =
* transform(queryFuture, rowsFunction);}
*
* This overload, which does not accept an executor, uses {@code
* directExecutor}, a dangerous choice in some cases. See the discussion in
* the {@link ListenableFuture#addListener ListenableFuture.addListener}
* documentation. The documentation's warnings about "lightweight listeners"
* refer here to the work done during {@code Function.apply}.
*
*
The returned {@code Future} attempts to keep its cancellation state in
* sync with that of the input future. That is, if the returned {@code Future}
* is cancelled, it will attempt to cancel the input, and if the input is
* cancelled, the returned {@code Future} will receive a callback in which it
* will attempt to cancel itself.
*
*
An example use of this method is to convert a serializable object
* returned from an RPC into a POJO.
*
* @param input The future to transform
* @param function A Function to transform the results of the provided future
* to the results of the returned future. This will be run in the thread
* that notifies input it is complete.
* @return A future that holds result of the transformation.
* @since 9.0 (in 1.0 as {@code compose})
*/
public static ListenableFuture transform(ListenableFuture input,
final Function function) {
checkNotNull(function);
ChainingFuture output = new ChainingFuture(input, function);
input.addListener(output, directExecutor());
return output;
}
/**
* Returns a new {@code ListenableFuture} whose result is the product of
* applying the given {@code Function} to the result of the given {@code
* Future}. Example:
*
* {@code
* ListenableFuture queryFuture = ...;
* Function> rowsFunction =
* new Function>() {
* public List apply(QueryResult queryResult) {
* return queryResult.getRows();
* }
* };
* ListenableFuture> rowsFuture =
* transform(queryFuture, rowsFunction, executor);}
*
* When selecting an executor, note that {@code directExecutor} is
* dangerous in some cases. See the discussion in the {@link
* ListenableFuture#addListener ListenableFuture.addListener} documentation.
* The documentation's warnings about "lightweight listeners" refer here to
* the work done during {@code Function.apply}.
*
*
The returned {@code Future} attempts to keep its cancellation state in
* sync with that of the input future. That is, if the returned {@code Future}
* is cancelled, it will attempt to cancel the input, and if the input is
* cancelled, the returned {@code Future} will receive a callback in which it
* will attempt to cancel itself.
*
*
An example use of this method is to convert a serializable object
* returned from an RPC into a POJO.
*
* @param input The future to transform
* @param function A Function to transform the results of the provided future
* to the results of the returned future.
* @param executor Executor to run the function in.
* @return A future that holds result of the transformation.
* @since 9.0 (in 2.0 as {@code compose})
*/
public static ListenableFuture transform(ListenableFuture input,
final Function function, Executor executor) {
checkNotNull(function);
ChainingFuture output = new ChainingFuture(input, function);
input.addListener(output, rejectionPropagatingExecutor(executor, output));
return output;
}
/**
* Like {@link #transform(ListenableFuture, Function)} except that the
* transformation {@code function} is invoked on each call to
* {@link Future#get() get()} on the returned future.
*
* The returned {@code Future} reflects the input's cancellation
* state directly, and any attempt to cancel the returned Future is likewise
* passed through to the input Future.
*
*
Note that calls to {@linkplain Future#get(long, TimeUnit) timed get}
* only apply the timeout to the execution of the underlying {@code Future},
* not to the execution of the transformation function.
*
*
The primary audience of this method is callers of {@code transform}
* who don't have a {@code ListenableFuture} available and
* do not mind repeated, lazy function evaluation.
*
* @param input The future to transform
* @param function A Function to transform the results of the provided future
* to the results of the returned future.
* @return A future that returns the result of the transformation.
* @since 10.0
*/
@GwtIncompatible("TODO")
@CheckReturnValue
public static Future lazyTransform(final Future input,
final Function function) {
checkNotNull(input);
checkNotNull(function);
return new Future() {
@Override
public boolean cancel(boolean mayInterruptIfRunning) {
return input.cancel(mayInterruptIfRunning);
}
@Override
public boolean isCancelled() {
return input.isCancelled();
}
@Override
public boolean isDone() {
return input.isDone();
}
@Override
public O get() throws InterruptedException, ExecutionException {
return applyTransformation(input.get());
}
@Override
public O get(long timeout, TimeUnit unit)
throws InterruptedException, ExecutionException, TimeoutException {
return applyTransformation(input.get(timeout, unit));
}
private O applyTransformation(I input) throws ExecutionException {
try {
return function.apply(input);
} catch (Throwable t) {
throw new ExecutionException(t);
}
}
};
}
/**
* An implementation of {@code ListenableFuture} that also implements
* {@code Runnable} so that it can be used to nest ListenableFutures.
* Once the passed-in {@code ListenableFuture} is complete, it calls the
* passed-in {@code Function} to generate the result.
*
* For historical reasons, this class has a special case in its exception
* handling: If the given {@code AsyncFunction} throws an {@code
* UndeclaredThrowableException}, {@code ChainingListenableFuture} unwraps it
* and uses its cause as the output future's exception, rather than
* using the {@code UndeclaredThrowableException} itself as it would for other
* exception types. The reason for this is that {@code Futures.transform} used
* to require a {@code Function}, whose {@code apply} method is not allowed to
* throw checked exceptions. Nowadays, {@code Futures.transform} has an
* overload that accepts an {@code AsyncFunction}, whose {@code apply} method
* is allowed to throw checked exception. Users who wish to throw
* checked exceptions should use that overload instead, and we
* should remove the {@code UndeclaredThrowableException} special case .
*/
private abstract static class AbstractChainingFuture
extends AbstractFuture.TrustedFutureimplements Runnable {
// In theory, this field might not be visible to a cancel() call in certain circumstances. For
// details, see the comments on the fields of TimeoutFuture.
@Nullable
ListenableFuture inputFuture;
@Nullable
F function;
AbstractChainingFuture(ListenableFuture inputFuture, F function) {
this.inputFuture = checkNotNull(inputFuture);
this.function = checkNotNull(function);
}
@Override
public final void run() {
try {
ListenableFuture localInputFuture = inputFuture;
F localFunction = function;
if (isCancelled() | localInputFuture == null | localFunction == null) {
return;
}
inputFuture = null;
function = null;
I sourceResult;
try {
sourceResult = getUninterruptibly(localInputFuture);
} catch (CancellationException e) {
// 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;
}
doTransform(localFunction, sourceResult);
} catch (UndeclaredThrowableException e) {
// Set the cause of the exception as this future's exception
setException(e.getCause());
} catch (Throwable t) {
// This exception is irrelevant in this thread, but useful for the
// client
setException(t);
}
}
/** Template method for subtypes to actually run the transform. */
abstract void doTransform(F function, I result) throws Exception;
@Override
final void done() {
maybePropagateCancellation(inputFuture);
this.inputFuture = null;
this.function = null;
}
}
/**
* A {@link AbstractChainingFuture} that delegates to an {@link AsyncFunction} and
* {@link #setFuture(ListenableFuture)} to implement {@link #doTransform}.
*/
private static final class AsyncChainingFuture
extends AbstractChainingFuture> {
AsyncChainingFuture(ListenableFuture inputFuture,
AsyncFunction function) {
super(inputFuture, function);
}
@Override
void doTransform(AsyncFunction function, 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)?");
setFuture(outputFuture);
}
}
/**
* A {@link AbstractChainingFuture} that delegates to a {@link Function} and
* {@link #set(Object)} to implement {@link #doTransform}.
*/
private static final class ChainingFuture
extends AbstractChainingFuture> {
ChainingFuture(ListenableFuture inputFuture,
Function function) {
super(inputFuture, function);
}
@Override
void doTransform(Function function, I input) {
// TODO(lukes): move the UndeclaredThrowable catch block here?
set(function.apply(input));
}
}
/**
* Returns a new {@code ListenableFuture} whose result is the product of
* calling {@code get()} on the {@code Future} nested within the given {@code
* Future}, effectively chaining the futures one after the other. Example:
*
* {@code
* SettableFuture> nested = SettableFuture.create();
* ListenableFuture dereferenced = dereference(nested);}
*
* This call has the same cancellation and execution semantics as {@link
* #transformAsync(ListenableFuture, AsyncFunction)}, in that the returned {@code
* Future} attempts to keep its cancellation state in sync with both the
* input {@code Future} and the nested {@code Future}. The transformation
* is very lightweight and therefore takes place in the same thread (either
* the thread that called {@code dereference}, or the thread in which the
* dereferenced future completes).
*
* @param nested The nested future to transform.
* @return A future that holds result of the inner future.
* @since 13.0
*/
@SuppressWarnings({"rawtypes", "unchecked"})
@CheckReturnValue
public static ListenableFuture dereference(
ListenableFuture> nested) {
return transformAsync((ListenableFuture) nested, (AsyncFunction) DEREFERENCER);
}
/**
* Helper {@code Function} for {@link #dereference}.
*/
private static final AsyncFunction, Object> DEREFERENCER = new AsyncFunction, Object>() {
@Override
public ListenableFuture apply(ListenableFuture input) {
return input;
}
};
/**
* Creates a new {@code ListenableFuture} whose value is a list containing the
* values of all its input futures, if all succeed. If any input fails, the
* returned future fails immediately.
*
* The list of results is in the same order as the input list.
*
*
Canceling this future will attempt to cancel all the component futures,
* and if any of the provided futures fails or is canceled, this one is,
* too.
*
* @param futures futures to combine
* @return a future that provides a list of the results of the component
* futures
* @since 10.0
*/
@Beta
@SafeVarargs
@CheckReturnValue
public static ListenableFuture> allAsList(
ListenableFuture... futures) {
return new ListFuture(ImmutableList.copyOf(futures), true);
}
/**
* Creates a new {@code ListenableFuture} whose value is a list containing the
* values of all its input futures, if all succeed. If any input fails, the
* returned future fails immediately.
*
* The list of results is in the same order as the input list.
*
*
Canceling this future will attempt to cancel all the component futures,
* and if any of the provided futures fails or is canceled, this one is,
* too.
*
* @param futures futures to combine
* @return a future that provides a list of the results of the component
* futures
* @since 10.0
*/
@Beta
@CheckReturnValue
public static ListenableFuture> allAsList(
Iterable> futures) {
return new ListFuture(ImmutableList.copyOf(futures), true);
}
/**
* Creates a new {@code ListenableFuture} whose result is set from the
* supplied future when it completes. Cancelling the supplied future
* will also cancel the returned future, but cancelling the returned
* future will have no effect on the supplied future.
*
* @since 15.0
*/
@GwtIncompatible("TODO")
@CheckReturnValue
public static ListenableFuture nonCancellationPropagating(
ListenableFuture future) {
return new NonCancellationPropagatingFuture(future);
}
/**
* A wrapped future that does not propagate cancellation to its delegate.
*/
@GwtIncompatible("TODO")
private static final class NonCancellationPropagatingFuture
extends AbstractFuture.TrustedFuture {
NonCancellationPropagatingFuture(final ListenableFuture delegate) {
delegate.addListener(new Runnable() {
@Override
public void run() {
// This prevents cancellation from propagating because we don't assign delegate until
// delegate is already done, so calling cancel() on it is a no-op.
setFuture(delegate);
}
}, directExecutor());
}
}
/**
* Creates a new {@code ListenableFuture} whose value is a list containing the
* values of all its successful input futures. The list of results is in the
* same order as the input list, and if any of the provided futures fails or
* is canceled, its corresponding position will contain {@code null} (which is
* indistinguishable from the future having a successful value of
* {@code null}).
*
* Canceling this future will attempt to cancel all the component futures.
*
* @param futures futures to combine
* @return a future that provides a list of the results of the component
* futures
* @since 10.0
*/
@Beta
@SafeVarargs
@CheckReturnValue
public static ListenableFuture> successfulAsList(
ListenableFuture... futures) {
return new ListFuture(ImmutableList.copyOf(futures), false);
}
/**
* Creates a new {@code ListenableFuture} whose value is a list containing the
* values of all its successful input futures. The list of results is in the
* same order as the input list, and if any of the provided futures fails or
* is canceled, its corresponding position will contain {@code null} (which is
* indistinguishable from the future having a successful value of
* {@code null}).
*
* Canceling this future will attempt to cancel all the component futures.
*
* @param futures futures to combine
* @return a future that provides a list of the results of the component
* futures
* @since 10.0
*/
@Beta
@CheckReturnValue
public static ListenableFuture> successfulAsList(
Iterable> futures) {
return new ListFuture(ImmutableList.copyOf(futures), false);
}
/**
* Returns a list of delegate futures that correspond to the futures received in the order
* that they complete. Delegate futures return the same value or throw the same exception
* as the corresponding input future returns/throws.
*
* Cancelling a delegate future has no effect on any input future, since the delegate future
* does not correspond to a specific input future until the appropriate number of input
* futures have completed. At that point, it is too late to cancel the input future.
* The input future's result, which cannot be stored into the cancelled delegate future,
* is ignored.
*
* @since 17.0
*/
@Beta
@GwtIncompatible("TODO")
@CheckReturnValue
public static ImmutableList> inCompletionOrder(
Iterable> futures) {
// A CLQ may be overkill here. We could save some pointers/memory by synchronizing on an
// ArrayDeque
final ConcurrentLinkedQueue> delegates = Queues.newConcurrentLinkedQueue();
ImmutableList.Builder> listBuilder = ImmutableList.builder();
// Using SerializingExecutor here will ensure that each CompletionOrderListener executes
// atomically and therefore that each returned future is guaranteed to be in completion order.
// N.B. there are some cases where the use of this executor could have possibly surprising
// effects when input futures finish at approximately the same time _and_ the output futures
// have directExecutor listeners. In this situation, the listeners may end up running on a
// different thread than if they were attached to the corresponding input future. We believe
// this to be a negligible cost since:
// 1. Using the directExecutor implies that your callback is safe to run on any thread.
// 2. This would likely only be noticeable if you were doing something expensive or blocking on
// a directExecutor listener on one of the output futures which is an antipattern anyway.
SerializingExecutor executor = new SerializingExecutor(directExecutor());
for (final ListenableFuture future : futures) {
SettableFuture delegate = SettableFuture.create();
// Must make sure to add the delegate to the queue first in case the future is already done
delegates.add(delegate);
future.addListener(new Runnable() {
@Override
public void run() {
delegates.remove().setFuture(future);
}
}, executor);
listBuilder.add(delegate);
}
return listBuilder.build();
}
/**
* Registers separate success and failure callbacks to be run when the {@code
* Future}'s computation is {@linkplain java.util.concurrent.Future#isDone()
* complete} or, if the computation is already complete, immediately.
*
* There is no guaranteed ordering of execution of callbacks, but any
* callback added through this method is guaranteed to be called once the
* computation is complete.
*
* Example:
{@code
* ListenableFuture future = ...;
* addCallback(future,
* new FutureCallback {
* public void onSuccess(QueryResult result) {
* storeInCache(result);
* }
* public void onFailure(Throwable t) {
* reportError(t);
* }
* });}
*
* This overload, which does not accept an executor, uses {@code
* directExecutor}, a dangerous choice in some cases. See the discussion in
* the {@link ListenableFuture#addListener ListenableFuture.addListener}
* documentation.
*
*
For a more general interface to attach a completion listener to a
* {@code Future}, see {@link ListenableFuture#addListener addListener}.
*
* @param future The future attach the callback to.
* @param callback The callback to invoke when {@code future} is completed.
* @since 10.0
*/
public static void addCallback(ListenableFuture future,
FutureCallback callback) {
addCallback(future, callback, directExecutor());
}
/**
* Registers separate success and failure callbacks to be run when the {@code
* Future}'s computation is {@linkplain java.util.concurrent.Future#isDone()
* complete} or, if the computation is already complete, immediately.
*
* The callback is run in {@code executor}.
* There is no guaranteed ordering of execution of callbacks, but any
* callback added through this method is guaranteed to be called once the
* computation is complete.
*
* Example:
{@code
* ListenableFuture future = ...;
* Executor e = ...
* addCallback(future,
* new FutureCallback {
* public void onSuccess(QueryResult result) {
* storeInCache(result);
* }
* public void onFailure(Throwable t) {
* reportError(t);
* }
* }, e);}
*
* When selecting an executor, note that {@code directExecutor} is
* dangerous in some cases. See the discussion in the {@link
* ListenableFuture#addListener ListenableFuture.addListener} documentation.
*
*
For a more general interface to attach a completion listener to a
* {@code Future}, see {@link ListenableFuture#addListener addListener}.
*
* @param future The future attach the callback to.
* @param callback The callback to invoke when {@code future} is completed.
* @param executor The executor to run {@code callback} when the future
* completes.
* @since 10.0
*/
public static void addCallback(final ListenableFuture future,
final FutureCallback callback, Executor executor) {
Preconditions.checkNotNull(callback);
Runnable callbackListener = new Runnable() {
@Override
public void run() {
final V value;
try {
// TODO(user): (Before Guava release), validate that this
// is the thing for IE.
value = getUninterruptibly(future);
} catch (ExecutionException e) {
callback.onFailure(e.getCause());
return;
} catch (RuntimeException e) {
callback.onFailure(e);
return;
} catch (Error e) {
callback.onFailure(e);
return;
}
callback.onSuccess(value);
}
};
future.addListener(callbackListener, executor);
}
/**
* Returns the result of {@link Future#get()}, converting most exceptions to a
* new instance of the given checked exception type. This reduces boilerplate
* for a common use of {@code Future} in which it is unnecessary to
* programmatically distinguish between exception types or to extract other
* information from the exception instance.
*
* Exceptions from {@code Future.get} are treated as follows:
*
* Any {@link ExecutionException} has its cause wrapped in an
* {@code X} if the cause is a checked exception, an {@link
* UncheckedExecutionException} if the cause is a {@code
* RuntimeException}, or an {@link ExecutionError} if the cause is an
* {@code Error}.
* Any {@link InterruptedException} is wrapped in an {@code X} (after
* restoring the interrupt).
* Any {@link CancellationException} is propagated untouched, as is any
* other {@link RuntimeException} (though {@code get} implementations are
* discouraged from throwing such exceptions).
*
*
* The overall principle is to continue to treat every checked exception as a
* checked exception, every unchecked exception as an unchecked exception, and
* every error as an error. In addition, the cause of any {@code
* ExecutionException} is wrapped in order to ensure that the new stack trace
* matches that of the current thread.
*
*
Instances of {@code exceptionClass} are created by choosing an arbitrary
* public constructor that accepts zero or more arguments, all of type {@code
* String} or {@code Throwable} (preferring constructors with at least one
* {@code String}) and calling the constructor via reflection. If the
* exception did not already have a cause, one is set by calling {@link
* Throwable#initCause(Throwable)} on it. If no such constructor exists, an
* {@code IllegalArgumentException} is thrown.
*
* @throws X if {@code get} throws any checked exception except for an {@code
* ExecutionException} whose cause is not itself a checked exception
* @throws UncheckedExecutionException if {@code get} throws an {@code
* ExecutionException} with a {@code RuntimeException} as its cause
* @throws ExecutionError if {@code get} throws an {@code ExecutionException}
* with an {@code Error} as its cause
* @throws CancellationException if {@code get} throws a {@code
* CancellationException}
* @throws IllegalArgumentException if {@code exceptionClass} extends {@code
* RuntimeException} or does not have a suitable constructor
* @since 19.0 (in 10.0 as {@code get})
*/
@GwtIncompatible("reflection")
public static V getChecked(
Future future, Class exceptionClass) throws X {
return FuturesGetChecked.getChecked(future, exceptionClass);
}
/**
* Returns the result of {@link Future#get(long, TimeUnit)}, converting most
* exceptions to a new instance of the given checked exception type. This
* reduces boilerplate for a common use of {@code Future} in which it is
* unnecessary to programmatically distinguish between exception types or to
* extract other information from the exception instance.
*
* Exceptions from {@code Future.get} are treated as follows:
*
* Any {@link ExecutionException} has its cause wrapped in an
* {@code X} if the cause is a checked exception, an {@link
* UncheckedExecutionException} if the cause is a {@code
* RuntimeException}, or an {@link ExecutionError} if the cause is an
* {@code Error}.
* Any {@link InterruptedException} is wrapped in an {@code X} (after
* restoring the interrupt).
* Any {@link TimeoutException} is wrapped in an {@code X}.
* Any {@link CancellationException} is propagated untouched, as is any
* other {@link RuntimeException} (though {@code get} implementations are
* discouraged from throwing such exceptions).
*
*
* The overall principle is to continue to treat every checked exception as a
* checked exception, every unchecked exception as an unchecked exception, and
* every error as an error. In addition, the cause of any {@code
* ExecutionException} is wrapped in order to ensure that the new stack trace
* matches that of the current thread.
*
*
Instances of {@code exceptionClass} are created by choosing an arbitrary
* public constructor that accepts zero or more arguments, all of type {@code
* String} or {@code Throwable} (preferring constructors with at least one
* {@code String}) and calling the constructor via reflection. If the
* exception did not already have a cause, one is set by calling {@link
* Throwable#initCause(Throwable)} on it. If no such constructor exists, an
* {@code IllegalArgumentException} is thrown.
*
* @throws X if {@code get} throws any checked exception except for an {@code
* ExecutionException} whose cause is not itself a checked exception
* @throws UncheckedExecutionException if {@code get} throws an {@code
* ExecutionException} with a {@code RuntimeException} as its cause
* @throws ExecutionError if {@code get} throws an {@code ExecutionException}
* with an {@code Error} as its cause
* @throws CancellationException if {@code get} throws a {@code
* CancellationException}
* @throws IllegalArgumentException if {@code exceptionClass} extends {@code
* RuntimeException} or does not have a suitable constructor
* @since 19.0 (in 10.0 as {@code get} and with different parameter order)
*/
@GwtIncompatible("reflection")
public static V getChecked(
Future future, Class exceptionClass, long timeout, TimeUnit unit)
throws X {
return FuturesGetChecked.getChecked(future, exceptionClass, timeout, unit);
}
/**
* Returns the result of calling {@link Future#get()} uninterruptibly on a
* task known not to throw a checked exception. This makes {@code Future} more
* suitable for lightweight, fast-running tasks that, barring bugs in the
* code, will not fail. This gives it exception-handling behavior similar to
* that of {@code ForkJoinTask.join}.
*
* Exceptions from {@code Future.get} are treated as follows:
*
* Any {@link ExecutionException} has its cause wrapped in an
* {@link UncheckedExecutionException} (if the cause is an {@code
* Exception}) or {@link ExecutionError} (if the cause is an {@code
* Error}).
* Any {@link InterruptedException} causes a retry of the {@code get}
* call. The interrupt is restored before {@code getUnchecked} returns.
* Any {@link CancellationException} is propagated untouched. So is any
* other {@link RuntimeException} ({@code get} implementations are
* discouraged from throwing such exceptions).
*
*
* The overall principle is to eliminate all checked exceptions: to loop to
* avoid {@code InterruptedException}, to pass through {@code
* CancellationException}, and to wrap any exception from the underlying
* computation in an {@code UncheckedExecutionException} or {@code
* ExecutionError}.
*
*
For an uninterruptible {@code get} that preserves other exceptions, see
* {@link Uninterruptibles#getUninterruptibly(Future)}.
*
* @throws UncheckedExecutionException if {@code get} throws an {@code
* ExecutionException} with an {@code Exception} as its cause
* @throws ExecutionError if {@code get} throws an {@code ExecutionException}
* with an {@code Error} as its cause
* @throws CancellationException if {@code get} throws a {@code
* CancellationException}
* @since 10.0
*/
@GwtIncompatible("TODO")
public static V getUnchecked(Future future) {
checkNotNull(future);
try {
return getUninterruptibly(future);
} catch (ExecutionException e) {
wrapAndThrowUnchecked(e.getCause());
throw new AssertionError();
}
}
@GwtIncompatible("TODO")
private static void wrapAndThrowUnchecked(Throwable cause) {
if (cause instanceof Error) {
throw new ExecutionError((Error) cause);
}
/*
* It's a non-Error, non-Exception Throwable. From my survey of such
* classes, I believe that most users intended to extend Exception, so we'll
* treat it like an Exception.
*/
throw new UncheckedExecutionException(cause);
}
/*
* Arguably we don't need a timed getUnchecked because any operation slow
* enough to require a timeout is heavyweight enough to throw a checked
* exception and therefore be inappropriate to use with getUnchecked. Further,
* it's not clear that converting the checked TimeoutException to a
* RuntimeException -- especially to an UncheckedExecutionException, since it
* wasn't thrown by the computation -- makes sense, and if we don't convert
* it, the user still has to write a try-catch block.
*
* If you think you would use this method, let us know. You might also also
* look into the Fork-Join framework:
* http://docs.oracle.com/javase/tutorial/essential/concurrency/forkjoin.html
*/
/** Used for {@link #allAsList} and {@link #successfulAsList}. */
private static final class ListFuture extends CollectionFuture> {
ListFuture(ImmutableCollection> futures,
boolean allMustSucceed) {
init(new ListFutureRunningState(futures, allMustSucceed));
}
private final class ListFutureRunningState extends CollectionFutureRunningState {
ListFutureRunningState(ImmutableCollection> futures,
boolean allMustSucceed) {
super(futures, allMustSucceed);
}
@Override
public List combine(List> values) {
List result = Lists.newArrayList();
for (Optional element : values) {
result.add(element != null ? element.orElse(null) : null);
}
return Collections.unmodifiableList(result);
}
}
}
/**
* A checked future that uses a function to map from exceptions to the
* appropriate checked type.
*/
@GwtIncompatible("TODO")
private static class MappingCheckedFuture extends
AbstractCheckedFuture {
final Function mapper;
MappingCheckedFuture(ListenableFuture delegate,
Function mapper) {
super(delegate);
this.mapper = checkNotNull(mapper);
}
@Override
protected X mapException(Exception e) {
return mapper.apply(e);
}
}
}
