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/*******************************************************************************
* Copyright (c) Contributors to the Eclipse Foundation
*
* 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.
*
* SPDX-License-Identifier: Apache-2.0
*******************************************************************************/
package org.osgi.util.promise;
import static java.util.Objects.requireNonNull;
import java.util.concurrent.CompletableFuture;
import java.util.concurrent.CompletionStage;
import java.util.concurrent.ConcurrentLinkedQueue;
import java.util.concurrent.RejectedExecutionException;
import java.util.concurrent.ScheduledFuture;
import java.util.concurrent.TimeUnit;
import org.osgi.util.function.Consumer;
import org.osgi.util.function.Function;
import org.osgi.util.function.Predicate;
/**
* Abstract Promise implementation.
*
* This class is not used directly by clients. Clients should use
* {@link PromiseFactory} to create a {@link Promise}.
*
* @param The result type associated with the Promise.
* @ThreadSafe
* @author $Id: 47302e4cee8df3450be43cd8850bc188e25b4828 $
*/
abstract class PromiseImpl implements Promise {
/**
* The factory to use for callbacks and scheduled operations.
*/
private final PromiseFactory factory;
/**
* A ConcurrentLinkedQueue to hold the callbacks for this Promise, so no
* additional synchronization is required to write to or read from the
* queue.
*/
private final ConcurrentLinkedQueue callbacks;
/**
* Initialize this Promise.
*
* @param factory The factory to use for callbacks and scheduled
* operations.
*/
PromiseImpl(PromiseFactory factory) {
this.factory = requireNonNull(factory);
callbacks = new ConcurrentLinkedQueue<>();
}
/**
* Return a new {@link DeferredPromiseImpl} using the {@link PromiseFactory}
* of this PromiseImpl.
*
* @return A new DeferredPromiseImpl.
* @since 1.1
*/
DeferredPromiseImpl deferred() {
return new DeferredPromiseImpl<>(factory);
}
/**
* Return a new {@link ResolvedPromiseImpl} using the {@link PromiseFactory}
* of this PromiseImpl.
*
* @param v Value for the ResolvedPromiseImpl.
* @return A new ResolvedPromiseImpl.
* @since 1.1
*/
ResolvedPromiseImpl resolved(V v) {
return new ResolvedPromiseImpl<>(v, factory);
}
/**
* Return a new {@link FailedPromiseImpl} using the {@link PromiseFactory}
* of this PromiseImpl.
*
* @param f Failure for the FailedPromiseImpl.
* @return A new FailedPromiseImpl.
* @since 1.1
*/
FailedPromiseImpl failed(Throwable f) {
return new FailedPromiseImpl<>(f, factory);
}
/**
* Marker interface for internal callbacks which do not call user code and
* should be run on the current thread for an already resolved promise. Such
* internal callbacks should be directly called to resolve a
* DeferredPromiseImpl so that its {@link DeferredPromiseImpl#orDone()}
* method can convert it to a resolved {@link PromiseImpl} type for
* efficiency.
*
* @since 1.2
*/
interface InlineCallback {
// Internal callback that should be called inline for a resolved
// promise.
}
/**
* {@inheritDoc}
*/
@Override
public Promise onResolve(Runnable callback) {
requireNonNull(callback);
if (isDone() && ((callback instanceof InlineCallback)
|| factory.allowCurrentThread())) {
try {
callback.run();
} catch (Throwable t) {
uncaughtException(t);
}
} else {
callbacks.offer(callback);
notifyCallbacks(); // call any registered callbacks
}
return this;
}
/**
* Call any registered callbacks if this Promise is resolved.
*/
void notifyCallbacks() {
if (!isDone()) {
return; // return if not resolved
}
/*
* Note: multiple threads can be in this method removing callbacks from
* the queue and executing them, so the order in which callbacks are
* executed cannot be specified.
*/
for (Runnable callback; (callback = callbacks.poll()) != null;) {
execute(callback);
}
}
/**
* Execute a operation on the executor.
*
* @since 1.2
*/
void execute(Runnable operation) {
try {
try {
factory.executor().execute(operation);
} catch (RejectedExecutionException e) {
operation.run();
}
} catch (Throwable t) {
uncaughtException(t);
}
}
/**
* Schedule a operation on the scheduled executor.
*
* @since 1.1
*/
ScheduledFuture< ? > schedule(Runnable operation, long delay,
TimeUnit unit) {
try {
try {
return factory.scheduledExecutor().schedule(operation, delay,
unit);
} catch (RejectedExecutionException e) {
execute(operation);
}
} catch (Throwable t) {
uncaughtException(t);
}
return null;
}
/**
* Handle an uncaught exception from a Runnable.
*
* @param t The uncaught exception.
* @since 1.1
*/
static void uncaughtException(Throwable t) {
try {
Thread thread = Thread.currentThread();
thread.getUncaughtExceptionHandler().uncaughtException(thread, t);
} catch (Throwable ignored) {
// we ignore this
}
}
/**
* {@inheritDoc}
*/
@Override
public Promise onSuccess(Consumer< ? super T> success) {
return onResolve(new OnSuccess(success));
}
/**
* A callback used for the {@link #onSuccess(Consumer)} method.
*
* @Immutable
* @since 1.1
*/
private final class OnSuccess implements Runnable, Result {
private final Consumer< ? super T> success;
OnSuccess(Consumer< ? super T> success) {
this.success = requireNonNull(success);
}
@Override
public void run() {
result(this);
}
@Override
public void accept(T v, Throwable f) {
if (f == null) {
try {
success.accept(v);
} catch (Throwable e) {
uncaughtException(e);
}
}
}
}
/**
* {@inheritDoc}
*/
@Override
public Promise onFailure(Consumer< ? super Throwable> failure) {
return onResolve(new OnFailure(failure));
}
/**
* A callback used for the {@link #onFailure(Consumer)} method.
*
* @Immutable
* @since 1.1
*/
private final class OnFailure implements Runnable, Result {
private final Consumer< ? super Throwable> failure;
OnFailure(Consumer< ? super Throwable> failure) {
this.failure = requireNonNull(failure);
}
@Override
public void run() {
result(this);
}
@Override
public void accept(T v, Throwable f) {
if (f != null) {
try {
failure.accept(f);
} catch (Throwable e) {
uncaughtException(e);
}
}
}
}
/**
* {@inheritDoc}
*/
@Override
public Promise then(Success success, Failure failure) {
DeferredPromiseImpl chained = deferred();
onResolve(chained.new Then<>(this, success, failure));
return chained.orDone();
}
/**
* {@inheritDoc}
*/
@Override
public Promise then(Success success) {
return then(success, null);
}
/**
* {@inheritDoc}
*/
@Override
public Promise thenAccept(Consumer< ? super T> consumer) {
DeferredPromiseImpl chained = deferred();
onResolve(chained.new ThenAccept(this, consumer));
return chained.orDone();
}
/**
* {@inheritDoc}
*/
@Override
public Promise filter(Predicate predicate) {
DeferredPromiseImpl chained = deferred();
onResolve(chained.new Filter(this, predicate));
return chained.orDone();
}
/**
* {@inheritDoc}
*/
@Override
public Promise map(Function mapper) {
DeferredPromiseImpl chained = deferred();
onResolve(chained.new Map<>(this, mapper));
return chained.orDone();
}
/**
* {@inheritDoc}
*/
@Override
public Promise flatMap(Function> mapper) {
DeferredPromiseImpl chained = deferred();
onResolve(chained.new FlatMap<>(this, mapper));
return chained.orDone();
}
/**
* {@inheritDoc}
*/
@Override
public Promise recover(Function, ? extends T> recovery) {
DeferredPromiseImpl chained = deferred();
onResolve(chained.new Recover(this, recovery));
return chained.orDone();
}
/**
* {@inheritDoc}
*/
@Override
public Promise recoverWith(Function, Promise> recovery) {
DeferredPromiseImpl chained = deferred();
onResolve(chained.new RecoverWith(this, recovery));
return chained.orDone();
}
/**
* {@inheritDoc}
*/
@Override
public Promise fallbackTo(Promise fallback) {
DeferredPromiseImpl chained = deferred();
onResolve(chained.new FallbackTo(this, fallback));
return chained.orDone();
}
/**
* {@inheritDoc}
*/
@Override
public Promise timeout(long millis) {
DeferredPromiseImpl chained = deferred();
onResolve(chained.new Timeout(this, millis));
return chained.orDone();
}
/**
* {@inheritDoc}
*/
@Override
public Promise delay(long millis) {
DeferredPromiseImpl chained = deferred();
onResolve(chained.new Delay(this, millis));
return chained.orDone();
}
/**
* {@inheritDoc}
*/
@Override
public CompletionStage toCompletionStage() {
CompletableFuture completableFuture = new CompletableFuture<>();
onResolve(new ToCompletionStage(completableFuture));
return completableFuture;
}
/**
* A callback used for the {@link #toCompletionStage()} method.
*
* @Immutable
* @since 1.2
*/
private final class ToCompletionStage implements Runnable, Result {
private final CompletableFuture completableFuture;
ToCompletionStage(CompletableFuture completableFuture) {
this.completableFuture = requireNonNull(completableFuture);
}
@Override
public void run() {
result(this);
}
@Override
public void accept(T v, Throwable f) {
if (f == null) {
completableFuture.complete(v);
} else {
completableFuture.completeExceptionally(f);
}
}
}
/**
* A consumer of the result of a Promise.
*
* @since 1.2
*/
interface Result {
void accept(R value, Throwable fail);
}
/**
* Accept the result of this PromiseImpl.
*
* @since 1.2
*/
abstract void result(Result< ? super T> consumer);
/**
* Accept the result of the specified Promise.
*
* @since 1.2
*/
static void result(Promise< ? extends R> promise,
Result< ? super R> consumer) {
if (promise instanceof PromiseImpl) {
PromiseImpl< ? extends R> impl = (PromiseImpl< ? extends R>) promise;
impl.result(consumer);
return;
}
if (!promise.isDone()) {
consumer.accept(null, new AssertionError("promise not resolved"));
return;
}
R value;
Throwable fail;
final boolean interrupted = Thread.interrupted();
try {
fail = promise.getFailure();
value = (fail == null) ? promise.getValue() : null;
} catch (Throwable e) {
fail = e; // propagate new exception
value = null;
} finally {
if (interrupted) { // restore interrupt status
Thread.currentThread().interrupt();
}
}
consumer.accept(value, fail);
}
}