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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.internal.subscriptions;
import java.util.concurrent.atomic.*;
import org.reactivestreams.Subscription;
import hu.akarnokd.rxjava2.disposables.Disposable;
import hu.akarnokd.rxjava2.internal.util.BackpressureHelper;
/**
* A subscription implementation that arbitrates exactly one other Subscription and can
* hold a single disposable resource.
*
* All methods are thread-safe.
*/
public final class AsyncSubscription extends AtomicLong implements Subscription, Disposable {
/** */
private static final long serialVersionUID = 7028635084060361255L;
volatile Subscription actual;
static final AtomicReferenceFieldUpdater ACTUAL =
AtomicReferenceFieldUpdater.newUpdater(AsyncSubscription.class, Subscription.class, "actual");
volatile Disposable resource;
static final AtomicReferenceFieldUpdater RESOURCE =
AtomicReferenceFieldUpdater.newUpdater(AsyncSubscription.class, Disposable.class, "resource");
static final Subscription CANCELLED = new Subscription() {
@Override
public void request(long n) {
}
@Override
public void cancel() {
}
@Override
public String toString() {
return "AsyncSubscription.CANCELLED";
}
};
static final Disposable DISPOSED = new Disposable() {
@Override
public void dispose() {
}
@Override
public String toString() {
return "AsyncSubscription.DISPOSED";
};
};
public AsyncSubscription() {
}
public AsyncSubscription(Disposable resource) {
RESOURCE.lazySet(this, resource);
}
@Override
public void request(long n) {
Subscription s = actual;
if (s != null) {
s.request(n);
} else {
if (SubscriptionHelper.validateRequest(n)) {
return;
}
BackpressureHelper.add(this, n);
s = actual;
if (s != null) {
long mr = getAndSet(0L);
if (mr != 0L) {
s.request(mr);
}
}
}
}
@Override
public void cancel() {
Subscription s = actual;
if (s != CANCELLED) {
s = ACTUAL.getAndSet(this, CANCELLED);
if (s != CANCELLED && s != null) {
s.cancel();
}
}
Disposable d = resource;
if (d != DISPOSED) {
d = RESOURCE.getAndSet(this, DISPOSED);
if (d != CANCELLED && d != null) {
d.dispose();
}
}
}
@Override
public void dispose() {
cancel();
}
/**
* Sets a new resource and disposes the currently held resource.
* @param r the new resource to set
* @return false if this AyncSubscription has been cancelled/disposed
* @see #replaceResource(Disposable)
*/
public boolean setResource(Disposable r) {
for (;;) {
Disposable d = resource;
if (d == DISPOSED) {
if (r != null) {
r.dispose();
}
return false;
}
if (RESOURCE.compareAndSet(this, d, r)) {
if (d != null) {
d.dispose();
}
return true;
}
}
}
/**
* Replaces the currently held resource with the given new one without disposing the old.
* @param r the new resource to set
* @return false if this AsyncSubscription has been cancelled/disposed
*/
public boolean replaceResource(Disposable r) {
for (;;) {
Disposable d = resource;
if (d == DISPOSED) {
if (r != null) {
r.dispose();
}
return false;
}
if (RESOURCE.compareAndSet(this, d, r)) {
return true;
}
}
}
/**
* Sets the given subscription if there isn't any subscription held.
* @param s the first and only subscription to set
* @return false if this AsyncSubscription has been cancelled/disposed
*/
public boolean setSubscription(Subscription s) {
for (;;) {
Subscription a = actual;
if (a == CANCELLED) {
s.cancel();
return false;
}
if (a != null) {
s.cancel();
SubscriptionHelper.reportSubscriptionSet();
return true;
}
if (ACTUAL.compareAndSet(this, null, s)) {
long mr = getAndSet(0L);
if (mr != 0L) {
s.request(mr);
}
return true;
}
}
}
}