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/*
* Copyright (c) OSGi Alliance (2014). All Rights Reserved.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.osgi.util.promise;
import static org.osgi.util.promise.PromiseImpl.requireNonNull;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collection;
import java.util.List;
import java.util.concurrent.atomic.AtomicInteger;
/**
* Static helper methods for {@link Promise}s.
*
* @ThreadSafe
* @author $Id$
*/
public class Promises {
private Promises() {
// disallow object creation
}
/**
* Create a new Promise that has been resolved with the specified value.
*
* @param <T> The value type associated with the returned Promise.
* @param value The value of the resolved Promise.
* @return A new Promise that has been resolved with the specified value.
*/
public static <T> Promise<T> resolved(T value) {
return new PromiseImpl<T>(value, null);
}
/**
* Create a new Promise that has been resolved with the specified failure.
*
* @param <T> The value type associated with the returned Promise.
* @param failure The failure of the resolved Promise. Must not be
* {@code null}.
* @return A new Promise that has been resolved with the specified failure.
*/
public static <T> Promise<T> failed(Throwable failure) {
return new PromiseImpl<T>(null, requireNonNull(failure));
}
/**
* Create a new Promise that is a latch on the resolution of the specified
* Promises.
*
* <p>
* The new Promise acts as a gate and must be resolved after all of the
* specified Promises are resolved.
*
* @param <T> The value type of the List value associated with the returned
* Promise.
* @param <S> A subtype of the value type of the List value associated with
* the returned Promise.
* @param promises The Promises which must be resolved before the returned
* Promise must be resolved. Must not be {@code null} and all of the
* elements in the collection must not be {@code null}.
* @return A Promise that is resolved only when all the specified Promises
* are resolved. The returned Promise must be successfully resolved
* with a List of the values in the order of the specified Promises
* if all the specified Promises are successfully resolved. The List
* in the returned Promise is the property of the caller and is
* modifiable. The returned Promise must be resolved with a failure
* of {@link FailedPromisesException} if any of the specified
* Promises are resolved with a failure. The failure
* {@link FailedPromisesException} must contain all of the specified
* Promises which resolved with a failure.
*/
public static <T, S extends T> Promise<List<T>> all(Collection<Promise<S>> promises) {
if (promises.isEmpty()) {
List<T> result = new ArrayList<T>();
return resolved(result);
}
/* make a copy and capture the ordering */
List<Promise<? extends T>> list = new ArrayList<Promise<? extends T>>(promises);
PromiseImpl<List<T>> chained = new PromiseImpl<List<T>>();
All<T> all = new All<T>(chained, list);
for (Promise<? extends T> promise : list) {
promise.onResolve(all);
}
return chained;
}
/**
* Create a new Promise that is a latch on the resolution of the specified
* Promises.
*
* <p>
* The new Promise acts as a gate and must be resolved after all of the
* specified Promises are resolved.
*
* @param <T> The value type associated with the specified Promises.
* @param promises The Promises which must be resolved before the returned
* Promise must be resolved. Must not be {@code null} and all of the
* arguments must not be {@code null}.
* @return A Promise that is resolved only when all the specified Promises
* are resolved. The returned Promise must be successfully resolved
* with a List of the values in the order of the specified Promises
* if all the specified Promises are successfully resolved. The List
* in the returned Promise is the property of the caller and is
* modifiable. The returned Promise must be resolved with a failure
* of {@link FailedPromisesException} if any of the specified
* Promises are resolved with a failure. The failure
* {@link FailedPromisesException} must contain all of the specified
* Promises which resolved with a failure.
*/
public static <T> Promise<List<T>> all(Promise<? extends T>... promises) {
@SuppressWarnings("unchecked")
List<Promise<T>> list = Arrays.asList((Promise<T>[]) promises);
return all(list);
}
/**
* A callback used to resolve a Promise when the specified list of Promises
* are resolved for the {@link Promises#all(Collection)} method.
*
* @ThreadSafe
*/
private static final class All<T> implements Runnable {
private final PromiseImpl<List<T>> chained;
private final List<Promise<? extends T>> promises;
private final AtomicInteger promiseCount;
All(PromiseImpl<List<T>> chained, List<Promise<? extends T>> promises) {
this.chained = chained;
this.promises = promises;
this.promiseCount = new AtomicInteger(promises.size());
}
public void run() {
if (promiseCount.decrementAndGet() != 0) {
return;
}
List<T> result = new ArrayList<T>(promises.size());
List<Promise<?>> failed = new ArrayList<Promise<?>>(promises.size());
Throwable cause = null;
for (Promise<? extends T> promise : promises) {
Throwable failure;
T value;
try {
failure = promise.getFailure();
value = (failure != null) ? null : promise.getValue();
} catch (Throwable e) {
chained.resolve(null, e);
return;
}
if (failure != null) {
failed.add(promise);
if (cause == null) {
cause = failure;
}
} else {
result.add(value);
}
}
if (failed.isEmpty()) {
chained.resolve(result, null);
} else {
chained.resolve(null, new FailedPromisesException(failed, cause));
}
}
}
}
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