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/**
* Copyright 2015 David Karnok and Netflix, Inc.
*
* 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 hu.akarnokd.rxjava2.subscribers;
import java.util.concurrent.atomic.*;
import org.reactivestreams.*;
import hu.akarnokd.rxjava2.disposables.*;
import hu.akarnokd.rxjava2.internal.disposables.ListCompositeResource;
import hu.akarnokd.rxjava2.internal.functions.Objects;
import hu.akarnokd.rxjava2.internal.subscriptions.SubscriptionHelper;
import hu.akarnokd.rxjava2.internal.util.BackpressureHelper;
/**
* An abstract Subscriber implementation that allows asynchronous cancellation of its
* subscription.
*
* This implementation let's you chose if the AsyncObserver manages resources or not,
* thus saving memory on cases where there is no need for that.
*
*
All pre-implemented final methods are thread-safe.
*
* @param the value type
*/
public abstract class AsyncObserver implements Subscriber, Disposable {
/** The active subscription. */
private volatile Subscription s;
/** Updater of s. */
@SuppressWarnings("rawtypes")
private static final AtomicReferenceFieldUpdater S =
AtomicReferenceFieldUpdater.newUpdater(AsyncObserver.class, Subscription.class, "s");
/** The resource composite, can be null. */
private final ListCompositeResource resources;
/** Remembers the request(n) counts until a subscription arrives. */
@SuppressWarnings("unused")
private volatile long missedRequested;
/** The updater of missedRequested. */
@SuppressWarnings("rawtypes")
private static final AtomicLongFieldUpdater MISSED_REQUESTED =
AtomicLongFieldUpdater.newUpdater(AsyncObserver.class, "missedRequested");
/** The cancelled subscription indicator. */
private static final Subscription CANCELLED = new Subscription() {
@Override
public void request(long n) {
// deliberately no op
}
@Override
public void cancel() {
// deliberately no op
}
};
/**
* Constructs an AsyncObserver with resource support.
*/
public AsyncObserver() {
this(true);
}
/**
* Constructs an AsyncObserver and allows specifying if it should support resources or not.
* @param withResources true if resource support should be on.
*/
public AsyncObserver(boolean withResources) {
this.resources = withResources ? new ListCompositeResource(Disposables.consumeAndDispose()) : null;
}
/**
* Adds a resource to this AsyncObserver.
*
* Note that if the AsyncObserver doesn't manage resources, this method will
* throw an IllegalStateException. Use {@link #supportsResources()} to determine if
* this AsyncObserver manages resources or not.
*
* @param resource the resource to add
*
* @throws NullPointerException if resource is null
* @throws IllegalStateException if this AsyncObserver doesn't manage resources
* @see #supportsResources()
*/
public final void add(Disposable resource) {
Objects.requireNonNull(resource, "resource is null");
if (resources != null) {
add(resource);
} else {
resource.dispose();
throw new IllegalStateException("This AsyncObserver doesn't manage additional resources");
}
}
/**
* Returns true if this AsyncObserver supports resources added via the add() method.
* @return true if this AsyncObserver supports resources added via the add() method
* @see #add(Disposable)
*/
public final boolean supportsResources() {
return resources != null;
}
@Override
public final void onSubscribe(Subscription s) {
if (!S.compareAndSet(this, null, s)) {
s.cancel();
if (s != CANCELLED) {
SubscriptionHelper.reportSubscriptionSet();
}
return;
}
long mr = MISSED_REQUESTED.getAndSet(this, 0L);
if (mr != 0L) {
s.request(mr);
}
onStart();
}
/**
* Called once the upstream sets a Subscription on this AsyncObserver.
*
*
You can perform initialization at this moment. The default
* implementation requests Long.MAX_VALUE from upstream.
*/
protected void onStart() {
request(Long.MAX_VALUE);
}
/**
* Request the specified amount of elements from upstream.
*
*
This method can be called before the upstream calls onSubscribe().
* When the subscription happens, all missed requests are requested.
*
* @param n the request amount, must be positive
*/
protected final void request(long n) {
if (SubscriptionHelper.validateRequest(n)) {
return;
}
Subscription a = s;
if (a == null) {
BackpressureHelper.add(MISSED_REQUESTED, this, n);
a = s;
if (a != null) {
long mr = MISSED_REQUESTED.getAndSet(this, 0L);
if (mr != 0L) {
a.request(mr);
}
}
} else {
a.request(n);
}
}
/**
* Cancels the subscription (if any) and disposes the resources associated with
* this AsyncObserver (if any).
*
*
This method can be called before the upstream calls onSubscribe at which
* case the Subscription will be immediately cancelled.
*/
protected final void cancel() {
Subscription a = s;
if (a != CANCELLED) {
a = S.getAndSet(this, CANCELLED);
if (a != CANCELLED && a != null) {
a.cancel();
if (resources != null) {
resources.dispose();
}
}
}
}
@Override
public final void dispose() {
cancel();
}
/**
* Returns true if this AsyncObserver has been disposed/cancelled.
* @return true if this AsyncObserver has been disposed/cancelled
*/
public final boolean isDisposed() {
return s == CANCELLED;
}
}