/*
* 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.checkArgument;
import static com.google.common.base.Preconditions.checkNotNull;
import static com.google.common.base.Preconditions.checkState;
import static com.google.common.util.concurrent.MoreExecutors.sameThreadExecutor;
import static com.google.common.util.concurrent.Uninterruptibles.getUninterruptibly;
import static com.google.common.util.concurrent.Uninterruptibles.putUninterruptibly;
import static com.google.common.util.concurrent.Uninterruptibles.takeUninterruptibly;
import static java.lang.Thread.currentThread;
import static java.util.Arrays.asList;
import com.google.common.annotations.Beta;
import com.google.common.base.Function;
import com.google.common.base.Preconditions;
import com.google.common.collect.ImmutableList;
import com.google.common.collect.Lists;
import com.google.common.collect.Ordering;
import java.lang.reflect.Constructor;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.UndeclaredThrowableException;
import java.util.Arrays;
import java.util.List;
import java.util.concurrent.BlockingQueue;
import java.util.concurrent.CancellationException;
import java.util.concurrent.CountDownLatch;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.Executor;
import java.util.concurrent.Future;
import java.util.concurrent.LinkedBlockingQueue;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.TimeoutException;
import java.util.concurrent.atomic.AtomicInteger;
import javax.annotation.Nullable;
/**
* Static utility methods pertaining to the {@link Future} interface.
*
* <p>Many of these methods use the {@link ListenableFuture} API; consult the
* Guava User Guide article on <a href=
* "http://code.google.com/p/guava-libraries/wiki/ListenableFutureExplained">
* {@code ListenableFuture}</a>.
*
* @author Kevin Bourrillion
* @author Nishant Thakkar
* @author Sven Mawson
* @since 1.0
*/
@Beta
public final class Futures {
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.
*
* <p>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)
*/
public static <V, X extends Exception> CheckedFuture<V, X> makeChecked(
ListenableFuture<V> future, Function<Exception, X> mapper) {
return new MappingCheckedFuture<V, X>(checkNotNull(future), mapper);
}
/**
* 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}.
*/
public static <V> ListenableFuture<V> immediateFuture(@Nullable V value) {
SettableFuture<V> future = SettableFuture.create();
future.set(value);
return future;
}
/**
* Returns a {@code CheckedFuture} which has its value set immediately upon
* construction.
*
* <p>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.
*/
public static <V, X extends Exception> CheckedFuture<V, X>
immediateCheckedFuture(@Nullable V value) {
SettableFuture<V> future = SettableFuture.create();
future.set(value);
return Futures.makeChecked(future, new Function<Exception, X>() {
@Override
public X apply(Exception e) {
throw new AssertionError("impossible");
}
});
}
/**
* Returns a {@code ListenableFuture} which has an exception set immediately
* upon construction.
*
* <p>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}.
*
* @throws Error if the throwable is an {@link Error}.
*/
public static <V> ListenableFuture<V> immediateFailedFuture(
Throwable throwable) {
checkNotNull(throwable);
SettableFuture<V> future = SettableFuture.create();
future.setException(throwable);
return future;
}
/**
* Returns a {@code CheckedFuture} which has an exception set immediately upon
* construction.
*
* <p>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}, and calling {@code checkedGet()} will throw the
* provided exception itself.
*
* @throws Error if the throwable is an {@link Error}.
*/
public static <V, X extends Exception> CheckedFuture<V, X>
immediateFailedCheckedFuture(final X exception) {
checkNotNull(exception);
return makeChecked(Futures.<V>immediateFailedFuture(exception),
new Function<Exception, X>() {
@Override
public X apply(Exception e) {
return exception;
}
});
}
/**
* 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:
*
* <pre> {@code
* ListenableFuture<RowKey> rowKeyFuture = indexService.lookUp(query);
* AsyncFunction<RowKey, QueryResult> queryFunction =
* new AsyncFunction<RowKey, QueryResult>() {
* public ListenableFuture<QueryResult> apply(RowKey rowKey) {
* return dataService.read(rowKey);
* }
* };
* ListenableFuture<QueryResult> queryFuture =
* transform(rowKeyFuture, queryFunction);
* }</pre>
*
* Note: If the derived {@code Future} is slow or heavyweight to create
* (whether the {@code Future} itself is slow or heavyweight to complete is
* irrelevant), consider {@linkplain #transform(ListenableFuture,
* AsyncFunction, Executor) supplying an executor}. If you do not supply an
* executor, {@code transform} will use {@link
* MoreExecutors#sameThreadExecutor sameThreadExecutor}, which carries some
* caveats for heavier operations. For example, the call to {@code
* function.apply} may run on an unpredictable or undesirable thread:
*
* <ul>
* <li>If the input {@code Future} is done at the time {@code transform} is
* called, {@code transform} will call {@code function.apply} inline.
* <li>If the input {@code Future} is not yet done, {@code transform} will
* schedule {@code function.apply} to be run by the thread that completes the
* input {@code Future}, which may be an internal system thread such as an
* RPC network thread.
* </ul>
*
* Also note that, regardless of which thread executes {@code
* function.apply}, all other registered but unexecuted listeners are
* prevented from running during its execution, even if those listeners are
* to run in other executors.
*
* <p>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 11.0
*/
public static <I, O> ListenableFuture<O> transform(ListenableFuture<I> input,
AsyncFunction<? super I, ? extends O> function) {
return transform(input, function, MoreExecutors.sameThreadExecutor());
}
/**
* 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:
*
* <pre> {@code
* ListenableFuture<RowKey> rowKeyFuture = indexService.lookUp(query);
* AsyncFunction<RowKey, QueryResult> queryFunction =
* new AsyncFunction<RowKey, QueryResult>() {
* public ListenableFuture<QueryResult> apply(RowKey rowKey) {
* return dataService.read(rowKey);
* }
* };
* ListenableFuture<QueryResult> queryFuture =
* transform(rowKeyFuture, queryFunction, executor);
* }</pre>
*
* <p>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.
*
* <p>When the execution of {@code function.apply} is fast and lightweight
* (though the {@code Future} it returns need not meet these criteria),
* consider {@linkplain #transform(ListenableFuture, AsyncFunction) omitting
* the executor} or explicitly specifying {@code sameThreadExecutor}.
* However, be aware of the caveats documented in the link above.
*
* @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 11.0
*/
public static <I, O> ListenableFuture<O> transform(ListenableFuture<I> input,
AsyncFunction<? super I, ? extends O> function,
Executor executor) {
ChainingListenableFuture<I, O> output =
new ChainingListenableFuture<I, O>(function, input);
input.addListener(output, executor);
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:
*
* <pre> {@code
* ListenableFuture<QueryResult> queryFuture = ...;
* Function<QueryResult, List<Row>> rowsFunction =
* new Function<QueryResult, List<Row>>() {
* public List<Row> apply(QueryResult queryResult) {
* return queryResult.getRows();
* }
* };
* ListenableFuture<List<Row>> rowsFuture =
* transform(queryFuture, rowsFunction);
* }</pre>
*
* Note: If the transformation is slow or heavyweight, consider {@linkplain
* #transform(ListenableFuture, Function, Executor) supplying an executor}.
* If you do not supply an executor, {@code transform} will use {@link
* MoreExecutors#sameThreadExecutor sameThreadExecutor}, which carries some
* caveats for heavier operations. For example, the call to {@code
* function.apply} may run on an unpredictable or undesirable thread:
*
* <ul>
* <li>If the input {@code Future} is done at the time {@code transform} is
* called, {@code transform} will call {@code function.apply} inline.
* <li>If the input {@code Future} is not yet done, {@code transform} will
* schedule {@code function.apply} to be run by the thread that completes the
* input {@code Future}, which may be an internal system thread such as an
* RPC network thread.
* </ul>
*
* Also note that, regardless of which thread executes {@code
* function.apply}, all other registered but unexecuted listeners are
* prevented from running during its execution, even if those listeners are
* to run in other executors.
*
* <p>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.
*
* <p>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 <I, O> ListenableFuture<O> transform(ListenableFuture<I> input,
final Function<? super I, ? extends O> function) {
return transform(input, function, MoreExecutors.sameThreadExecutor());
}
/**
* 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:
*
* <pre> {@code
* ListenableFuture<QueryResult> queryFuture = ...;
* Function<QueryResult, List<Row>> rowsFunction =
* new Function<QueryResult, List<Row>>() {
* public List<Row> apply(QueryResult queryResult) {
* return queryResult.getRows();
* }
* };
* ListenableFuture<List<Row>> rowsFuture =
* transform(queryFuture, rowsFunction, executor);
* }</pre>
*
* <p>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.
*
* <p>An example use of this method is to convert a serializable object
* returned from an RPC into a POJO.
*
* <p>When the transformation is fast and lightweight, consider {@linkplain
* #transform(ListenableFuture, Function) omitting the executor} or
* explicitly specifying {@code sameThreadExecutor}. However, be aware of the
* caveats documented in the link above.
*
* @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 <I, O> ListenableFuture<O> transform(ListenableFuture<I> input,
final Function<? super I, ? extends O> function, Executor executor) {
checkNotNull(function);
AsyncFunction<I, O> wrapperFunction
= new AsyncFunction<I, O>() {
@Override public ListenableFuture<O> apply(I input) {
O output = function.apply(input);
return immediateFuture(output);
}
};
return transform(input, wrapperFunction, executor);
}
/**
* 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.
*
* <p>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.
*
* <p>Note that calls to {@linkplain Future#get(long, TimeUnit) timed get}
* only apply the timeout to the execution of the underlying {@code Future},
* <em>not</em> to the execution of the transformation function.
*
* <p>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
*/
@Beta
public static <I, O> Future<O> lazyTransform(final Future<I> input,
final Function<? super I, ? extends O> function) {
checkNotNull(input);
checkNotNull(function);
return new Future<O>() {
@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.
*
* <p>If the function throws any checked exceptions, they should be wrapped
* in a {@code UndeclaredThrowableException} so that this class can get
* access to the cause.
*/
private static class ChainingListenableFuture<I, O>
extends AbstractFuture<O> implements Runnable {
private AsyncFunction<? super I, ? extends O> function;
private ListenableFuture<? extends I> inputFuture;
private volatile ListenableFuture<? extends O> outputFuture;
private final BlockingQueue<Boolean> mayInterruptIfRunningChannel =
new LinkedBlockingQueue<Boolean>(1);
private final CountDownLatch outputCreated = new CountDownLatch(1);
private ChainingListenableFuture(
AsyncFunction<? super I, ? extends O> function,
ListenableFuture<? extends I> inputFuture) {
this.function = checkNotNull(function);
this.inputFuture = checkNotNull(inputFuture);
}
@Override
public boolean cancel(boolean mayInterruptIfRunning) {
/*
* Our additional cancellation work needs to occur even if
* !mayInterruptIfRunning, so we can't move it into interruptTask().
*/
if (super.cancel(mayInterruptIfRunning)) {
// This should never block since only one thread is allowed to cancel
// this Future.
putUninterruptibly(mayInterruptIfRunningChannel, mayInterruptIfRunning);
cancel(inputFuture, mayInterruptIfRunning);
cancel(outputFuture, mayInterruptIfRunning);
return true;
}
return false;
}
private void cancel(@Nullable Future<?> future,
boolean mayInterruptIfRunning) {
if (future != null) {
future.cancel(mayInterruptIfRunning);
}
}
@Override
public void run() {
try {
I sourceResult;
try {
sourceResult = getUninterruptibly(inputFuture);
} 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;
}
final ListenableFuture<? extends O> outputFuture = this.outputFuture =
function.apply(sourceResult);
if (isCancelled()) {
// Handles the case where cancel was called while the function was
// being applied.
// There is a gap in cancel(boolean) between calling sync.cancel()
// and storing the value of mayInterruptIfRunning, so this thread
// needs to block, waiting for that value.
outputFuture.cancel(
takeUninterruptibly(mayInterruptIfRunningChannel));
this.outputFuture = null;
return;
}
outputFuture.addListener(new Runnable() {
@Override
public void run() {
try {
// Here it would have been nice to have had an
// UninterruptibleListenableFuture, but we don't want to start a
// combinatorial explosion of interfaces, so we have to make do.
set(getUninterruptibly(outputFuture));
} catch (CancellationException e) {
// Cancel this future and return.
// At this point, inputFuture and outputFuture are done, 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());
} finally {
// Don't pin inputs beyond completion
ChainingListenableFuture.this.outputFuture = null;
}
}
}, MoreExecutors.sameThreadExecutor());
} catch (UndeclaredThrowableException e) {
// Set the cause of the exception as this future's exception
setException(e.getCause());
} catch (Exception e) {
// This exception is irrelevant in this thread, but useful for the
// client
setException(e);
} catch (Error e) {
// Propagate errors up ASAP - our superclass will rethrow the error
setException(e);
} finally {
// Don't pin inputs beyond completion
function = null;
inputFuture = null;
// Allow our get routines to examine outputFuture now.
outputCreated.countDown();
}
}
}
/**
* 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:
*
* <pre> {@code
* SettableFuture<ListenableFuture<String>> nested = SettableFuture.create();
* ListenableFuture<String> dereferenced = dereference(nested);
* }</pre>
*
* <p>This call has the same cancellation and execution semantics as {@link
* #transform(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 thread that called
* {@code dereference}.
*
* @param nested The nested future to transform.
* @return A future that holds result of the inner future.
* @since 13.0
*/
@Beta
@SuppressWarnings({"rawtypes", "unchecked"})
public static <V> ListenableFuture<V> dereference(
ListenableFuture<? extends ListenableFuture<? extends V>> nested) {
return Futures.transform((ListenableFuture) nested, (AsyncFunction) DEREFERENCER);
}
/**
* Helper {@code Function} for {@link #dereference}.
*/
private static final AsyncFunction<ListenableFuture<Object>, Object> DEREFERENCER =
new AsyncFunction<ListenableFuture<Object>, Object>() {
@Override public ListenableFuture<Object> apply(ListenableFuture<Object> 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.
*
* <p>The list of results is in the same order as the input list.
*
* <p>Canceling this future does not cancel any of the component futures;
* however, 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
public static <V> ListenableFuture<List<V>> allAsList(
ListenableFuture<? extends V>... futures) {
return new ListFuture<V>(ImmutableList.copyOf(futures), true,
MoreExecutors.sameThreadExecutor());
}
/**
* 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.
*
* <p>The list of results is in the same order as the input list.
*
* <p>Canceling this future does not cancel any of the component futures;
* however, 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
public static <V> ListenableFuture<List<V>> allAsList(
Iterable<? extends ListenableFuture<? extends V>> futures) {
return new ListFuture<V>(ImmutableList.copyOf(futures), true,
MoreExecutors.sameThreadExecutor());
}
/**
* 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}).
*
* @param futures futures to combine
* @return a future that provides a list of the results of the component
* futures
* @since 10.0
*/
@Beta
public static <V> ListenableFuture<List<V>> successfulAsList(
ListenableFuture<? extends V>... futures) {
return new ListFuture<V>(ImmutableList.copyOf(futures), false,
MoreExecutors.sameThreadExecutor());
}
/**
* 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}).
*
* @param futures futures to combine
* @return a future that provides a list of the results of the component
* futures
* @since 10.0
*/
@Beta
public static <V> ListenableFuture<List<V>> successfulAsList(
Iterable<? extends ListenableFuture<? extends V>> futures) {
return new ListFuture<V>(ImmutableList.copyOf(futures), false,
MoreExecutors.sameThreadExecutor());
}
/**
* 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.
*
* <p>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: <pre> {@code
* ListenableFuture<QueryResult> future = ...;
* addCallback(future,
* new FutureCallback<QueryResult> {
* public void onSuccess(QueryResult result) {
* storeInCache(result);
* }
* public void onFailure(Throwable t) {
* reportError(t);
* }
* });}</pre>
*
* Note: If the callback is slow or heavyweight, consider {@linkplain
* #addCallback(ListenableFuture, FutureCallback, Executor) supplying an
* executor}. If you do not supply an executor, {@code addCallback} will use
* {@link MoreExecutors#sameThreadExecutor sameThreadExecutor}, which carries
* some caveats for heavier operations. For example, the callback may run on
* an unpredictable or undesirable thread:
*
* <ul>
* <li>If the input {@code Future} is done at the time {@code addCallback} is
* called, {@code addCallback} will execute the callback inline.
* <li>If the input {@code Future} is not yet done, {@code addCallback} will
* schedule the callback to be run by the thread that completes the input
* {@code Future}, which may be an internal system thread such as an RPC
* network thread.
* </ul>
*
* Also note that, regardless of which thread executes the callback, all
* other registered but unexecuted listeners are prevented from running
* during its execution, even if those listeners are to run in other
* executors.
*
* <p>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 <V> void addCallback(ListenableFuture<V> future,
FutureCallback<? super V> callback) {
addCallback(future, callback, MoreExecutors.sameThreadExecutor());
}
/**
* 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.
*
* <p>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: <pre> {@code
* ListenableFuture<QueryResult> future = ...;
* Executor e = ...
* addCallback(future, e,
* new FutureCallback<QueryResult> {
* public void onSuccess(QueryResult result) {
* storeInCache(result);
* }
* public void onFailure(Throwable t) {
* reportError(t);
* }
* });}</pre>
*
* When the callback is fast and lightweight, consider {@linkplain
* #addCallback(ListenableFuture, FutureCallback) omitting the executor} or
* explicitly specifying {@code sameThreadExecutor}. However, be aware of the
* caveats documented in the link above.
*
* <p>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 <V> void addCallback(final ListenableFuture<V> future,
final FutureCallback<? super V> callback, Executor executor) {
Preconditions.checkNotNull(callback);
Runnable callbackListener = new Runnable() {
@Override
public void run() {
try {
// TODO(user): (Before Guava release), validate that this
// is the thing for IE.
V value = getUninterruptibly(future);
callback.onSuccess(value);
} catch (ExecutionException e) {
callback.onFailure(e.getCause());
} catch (RuntimeException e) {
callback.onFailure(e);
} catch (Error e) {
callback.onFailure(e);
}
}
};
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.
*
* <p>Exceptions from {@code Future.get} are treated as follows:
* <ul>
* <li>Any {@link ExecutionException} has its <i>cause</i> 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}.
* <li>Any {@link InterruptedException} is wrapped in an {@code X} (after
* restoring the interrupt).
* <li>Any {@link CancellationException} is propagated untouched, as is any
* other {@link RuntimeException} (though {@code get} implementations are
* discouraged from throwing such exceptions).
* </ul>
*
* 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.
*
* <p>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 10.0
*/
@Beta
public static <V, X extends Exception> V get(
Future<V> future, Class<X> exceptionClass) throws X {
checkNotNull(future);
checkArgument(!RuntimeException.class.isAssignableFrom(exceptionClass),
"Futures.get exception type (%s) must not be a RuntimeException",
exceptionClass);
try {
return future.get();
} catch (InterruptedException e) {
currentThread().interrupt();
throw newWithCause(exceptionClass, e);
} catch (ExecutionException e) {
wrapAndThrowExceptionOrError(e.getCause(), exceptionClass);
throw new AssertionError();
}
}
/**
* 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.
*
* <p>Exceptions from {@code Future.get} are treated as follows:
* <ul>
* <li>Any {@link ExecutionException} has its <i>cause</i> 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}.
* <li>Any {@link InterruptedException} is wrapped in an {@code X} (after
* restoring the interrupt).
* <li>Any {@link TimeoutException} is wrapped in an {@code X}.
* <li>Any {@link CancellationException} is propagated untouched, as is any
* other {@link RuntimeException} (though {@code get} implementations are
* discouraged from throwing such exceptions).
* </ul>
*
* 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.
*
* <p>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 10.0
*/
@Beta
public static <V, X extends Exception> V get(
Future<V> future, long timeout, TimeUnit unit, Class<X> exceptionClass)
throws X {
checkNotNull(future);
checkNotNull(unit);
checkArgument(!RuntimeException.class.isAssignableFrom(exceptionClass),
"Futures.get exception type (%s) must not be a RuntimeException",
exceptionClass);
try {
return future.get(timeout, unit);
} catch (InterruptedException e) {
currentThread().interrupt();
throw newWithCause(exceptionClass, e);
} catch (TimeoutException e) {
throw newWithCause(exceptionClass, e);
} catch (ExecutionException e) {
wrapAndThrowExceptionOrError(e.getCause(), exceptionClass);
throw new AssertionError();
}
}
private static <X extends Exception> void wrapAndThrowExceptionOrError(
Throwable cause, Class<X> exceptionClass) throws X {
if (cause instanceof Error) {
throw new ExecutionError((Error) cause);
}
if (cause instanceof RuntimeException) {
throw new UncheckedExecutionException(cause);
}
throw newWithCause(exceptionClass, cause);
}
/**
* 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}.
*
* <p>Exceptions from {@code Future.get} are treated as follows:
* <ul>
* <li>Any {@link ExecutionException} has its <i>cause</i> wrapped in an
* {@link UncheckedExecutionException} (if the cause is an {@code
* Exception}) or {@link ExecutionError} (if the cause is an {@code
* Error}).
* <li>Any {@link InterruptedException} causes a retry of the {@code get}
* call. The interrupt is restored before {@code getUnchecked} returns.
* <li>Any {@link CancellationException} is propagated untouched. So is any
* other {@link RuntimeException} ({@code get} implementations are
* discouraged from throwing such exceptions).
* </ul>
*
* 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}.
*
* <p>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
*/
@Beta
public static <V> V getUnchecked(Future<V> future) {
checkNotNull(future);
try {
return getUninterruptibly(future);
} catch (ExecutionException e) {
wrapAndThrowUnchecked(e.getCause());
throw new AssertionError();
}
}
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);
}
/*
* TODO(user): FutureChecker interface for these to be static methods on? If
* so, refer to it in the (static-method) Futures.get documentation
*/
/*
* 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.
*/
private static <X extends Exception> X newWithCause(
Class<X> exceptionClass, Throwable cause) {
// getConstructors() guarantees this as long as we don't modify the array.
@SuppressWarnings("unchecked")
List<Constructor<X>> constructors =
(List) Arrays.asList(exceptionClass.getConstructors());
for (Constructor<X> constructor : preferringStrings(constructors)) {
@Nullable X instance = newFromConstructor(constructor, cause);
if (instance != null) {
if (instance.getCause() == null) {
instance.initCause(cause);
}
return instance;
}
}
throw new IllegalArgumentException(
"No appropriate constructor for exception of type " + exceptionClass
+ " in response to chained exception", cause);
}
private static <X extends Exception> List<Constructor<X>>
preferringStrings(List<Constructor<X>> constructors) {
return WITH_STRING_PARAM_FIRST.sortedCopy(constructors);
}
private static final Ordering<Constructor<?>> WITH_STRING_PARAM_FIRST =
Ordering.natural().onResultOf(new Function<Constructor<?>, Boolean>() {
@Override public Boolean apply(Constructor<?> input) {
return asList(input.getParameterTypes()).contains(String.class);
}
}).reverse();
@Nullable private static <X> X newFromConstructor(
Constructor<X> constructor, Throwable cause) {
Class<?>[] paramTypes = constructor.getParameterTypes();
Object[] params = new Object[paramTypes.length];
for (int i = 0; i < paramTypes.length; i++) {
Class<?> paramType = paramTypes[i];
if (paramType.equals(String.class)) {
params[i] = cause.toString();
} else if (paramType.equals(Throwable.class)) {
params[i] = cause;
} else {
return null;
}
}
try {
return constructor.newInstance(params);
} catch (IllegalArgumentException e) {
return null;
} catch (InstantiationException e) {
return null;
} catch (IllegalAccessException e) {
return null;
} catch (InvocationTargetException e) {
return null;
}
}
/**
* Class that implements {@link #allAsList} and {@link #successfulAsList}.
* The idea is to create a (null-filled) List and register a listener with
* each component future to fill out the value in the List when that future
* completes.
*/
private static class ListFuture<V> extends AbstractFuture<List<V>> {
ImmutableList<? extends ListenableFuture<? extends V>> futures;
final boolean allMustSucceed;
final AtomicInteger remaining;
List<V> values;
/**
* Constructor.
*
* @param futures all the futures to build the list from
* @param allMustSucceed whether a single failure or cancellation should
* propagate to this future
* @param listenerExecutor used to run listeners on all the passed in
* futures.
*/
ListFuture(
final ImmutableList<? extends ListenableFuture<? extends V>> futures,
final boolean allMustSucceed, final Executor listenerExecutor) {
this.futures = futures;
this.values = Lists.newArrayListWithCapacity(futures.size());
this.allMustSucceed = allMustSucceed;
this.remaining = new AtomicInteger(futures.size());
init(listenerExecutor);
}
private void init(final Executor listenerExecutor) {
// First, schedule cleanup to execute when the Future is done.
addListener(new Runnable() {
@Override
public void run() {
// By now the values array has either been set as the Future's value,
// or (in case of failure) is no longer useful.
ListFuture.this.values = null;
// Let go of the memory held by other futures
ListFuture.this.futures = null;
}
}, MoreExecutors.sameThreadExecutor());
// Now begin the "real" initialization.
// Corner case: List is empty.
if (futures.isEmpty()) {
set(Lists.newArrayList(values));
return;
}
// Populate the results list with null initially.
for (int i = 0; i < futures.size(); ++i) {
values.add(null);
}
// Register a listener on each Future in the list to update
// the state of this future.
// Note that if all the futures on the list are done prior to completing
// this loop, the last call to addListener() will callback to
// setOneValue(), transitively call our cleanup listener, and set
// this.futures to null.
// We store a reference to futures to avoid the NPE.
ImmutableList<? extends ListenableFuture<? extends V>> localFutures = futures;
for (int i = 0; i < localFutures.size(); i++) {
final ListenableFuture<? extends V> listenable = localFutures.get(i);
final int index = i;
listenable.addListener(new Runnable() {
@Override
public void run() {
setOneValue(index, listenable);
}
}, listenerExecutor);
}
}
/**
* Sets the value at the given index to that of the given future.
*/
private void setOneValue(int index, Future<? extends V> future) {
List<V> localValues = values;
if (isDone() || localValues == null) {
// Some other future failed or has been cancelled, causing this one to
// also be cancelled or have an exception set. This should only happen
// if allMustSucceed is true.
checkState(allMustSucceed,
"Future was done before all dependencies completed");
return;
}
try {
checkState(future.isDone(),
"Tried to set value from future which is not done");
localValues.set(index, getUninterruptibly(future));
} catch (CancellationException e) {
if (allMustSucceed) {
// Set ourselves as cancelled. Let the input futures keep running
// as some of them may be used elsewhere.
// (Currently we don't override interruptTask, so
// mayInterruptIfRunning==false isn't technically necessary.)
cancel(false);
}
} catch (ExecutionException e) {
if (allMustSucceed) {
// As soon as the first one fails, throw the exception up.
// The result of all other inputs is then ignored.
setException(e.getCause());
}
} catch (RuntimeException e) {
if (allMustSucceed) {
setException(e);
}
} catch (Error e) {
// Propagate errors up ASAP - our superclass will rethrow the error
setException(e);
} finally {
int newRemaining = remaining.decrementAndGet();
checkState(newRemaining >= 0, "Less than 0 remaining futures");
if (newRemaining == 0) {
localValues = values;
if (localValues != null) {
set(Lists.newArrayList(localValues));
} else {
checkState(isDone());
}
}
}
}
}
/**
* A checked future that uses a function to map from exceptions to the
* appropriate checked type.
*/
private static class MappingCheckedFuture<V, X extends Exception> extends
AbstractCheckedFuture<V, X> {
final Function<Exception, X> mapper;
MappingCheckedFuture(ListenableFuture<V> delegate,
Function<Exception, X> mapper) {
super(delegate);
this.mapper = checkNotNull(mapper);
}
@Override
protected X mapException(Exception e) {
return mapper.apply(e);
}
}
}