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/*
* Copyright (C) 2012 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 jersey.repackaged.com.google.common.util.concurrent;
import static jersey.repackaged.com.google.common.base.Preconditions.checkNotNull;
import javax.annotation.Nullable;
/**
* A settable future that can be set asynchronously via {@link #setFuture}.
* A similar effect could be accomplished by adding a listener to the delegate
* future that sets a normal settable future after the delegate is complete.
* This approach gains us the ability to keep track of whether a delegate has
* been set (i.e. so that we can prevent collisions from setting it twice and
* can know before the computation is done whether it has been set), as well
* as improved cancellation semantics (i.e. if either future is cancelled,
* then the other one is too). This class is thread-safe.
*
* @param The result type returned by the Future's {@code get} method.
*
* @author Stephen Hicks
*/
final class AsyncSettableFuture extends ForwardingListenableFuture {
/** Creates a new asynchronously-settable future. */
public static AsyncSettableFuture create() {
return new AsyncSettableFuture();
}
private final NestedFuture nested = new NestedFuture();
private final ListenableFuture dereferenced = Futures.dereference(nested);
private AsyncSettableFuture() {}
@Override protected ListenableFuture delegate() {
return dereferenced;
}
/**
* Sets this future to forward to the given future. Returns {@code true}
* if the future was able to be set (i.e. it hasn't been set already).
*/
public boolean setFuture(ListenableFuture future) {
return nested.setFuture(checkNotNull(future));
}
/**
* Convenience method that calls {@link #setFuture} on a {@link
* Futures#immediateFuture}. Returns {@code true} if the future
* was able to be set (i.e. it hasn't been set already).
*/
public boolean setValue(@Nullable V value) {
return setFuture(Futures.immediateFuture(value));
}
/**
* Convenience method that calls {@link #setFuture} on a {@link
* Futures#immediateFailedFuture}. Returns {@code true} if the
* future was able to be set (i.e. it hasn't been set already).
*/
public boolean setException(Throwable exception) {
return setFuture(Futures.immediateFailedFuture(exception));
}
/**
* Returns {@code true} if this future has been (possibly asynchronously) set.
* Note that a {@code false} result in no way gaurantees that a later call
* to, e.g., {@link #setFuture} will succeed, since another thread could
* make the call in between. This is somewhat analogous to {@link #isDone},
* but since setting and completing are not the same event, it is useful to
* have this method broken out.
*/
public boolean isSet() {
return nested.isDone();
}
private static final class NestedFuture extends AbstractFuture> {
boolean setFuture(ListenableFuture value) {
boolean result = set(value);
if (isCancelled()) {
value.cancel(wasInterrupted());
}
return result;
}
}
}