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@jasennett
Created November 20, 2017 15:57
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DisposableSingleCache
import java.util.concurrent.atomic.AtomicBoolean;
import java.util.concurrent.atomic.AtomicInteger;
import java.util.concurrent.atomic.AtomicReference;
import io.reactivex.Single;
import io.reactivex.SingleObserver;
import io.reactivex.SingleSource;
import io.reactivex.disposables.Disposable;
public final class DisposableSingleCache<T> extends Single<T> implements SingleObserver<T>, Disposable
{
@SuppressWarnings("rawtypes")
static final CacheDisposable[] EMPTY = new CacheDisposable[0];
@SuppressWarnings("rawtypes")
static final CacheDisposable[] TERMINATED = new CacheDisposable[0];
@SuppressWarnings("rawtypes")
static final CacheDisposable[] DISPOSED = new CacheDisposable[0];
final SingleSource<? extends T> source;
final AtomicInteger wip;
final AtomicReference<CacheDisposable<T>[]> observers;
T value;
Throwable error;
private Disposable sourceDisposable;
private final Object disposeLock;
@SuppressWarnings("unchecked")
public DisposableSingleCache(SingleSource<? extends T> source) {
this.source = source;
this.wip = new AtomicInteger();
this.observers = new AtomicReference<CacheDisposable<T>[]>(EMPTY);
this.disposeLock = new Object();
}
@SuppressWarnings("unchecked")
@Override
public void dispose() {
CacheDisposable<T>[] previousObservers;
synchronized (disposeLock) {
for(;;) {
previousObservers = observers.get();
if (previousObservers == TERMINATED) {
break;
} else {
if (observers.compareAndSet(previousObservers, DISPOSED)) {
break;
}
}
}
}
if (previousObservers != DISPOSED && previousObservers != TERMINATED) {
if (sourceDisposable != null) {
sourceDisposable.dispose();
}
for (CacheDisposable<T> d : previousObservers) {
d.dispose();
}
}
}
@Override
public boolean isDisposed() {
return observers.get() == DISPOSED;
}
@Override
protected void subscribeActual(final SingleObserver<? super T> s) {
CacheDisposable<T> d = new CacheDisposable<T>(s, this);
s.onSubscribe(d);
if (add(d)) {
if (d.isDisposed()) {
remove(d);
}
} else {
if (observers.get() == DISPOSED) {
s.onError(new IllegalStateException("Source disposable already disposed"));
} else {
Throwable ex = error;
if (ex != null) {
s.onError(ex);
} else {
s.onSuccess(value);
}
}
return;
}
if (wip.getAndIncrement() == 0) {
source.subscribe(this);
}
}
boolean add(CacheDisposable<T> observer) {
for (;;) {
CacheDisposable<T>[] a = observers.get();
if (a == TERMINATED || a == DISPOSED) {
return false;
}
int n = a.length;
@SuppressWarnings("unchecked")
CacheDisposable<T>[] b = new CacheDisposable[n + 1];
System.arraycopy(a, 0, b, 0, n);
b[n] = observer;
if (observers.compareAndSet(a, b)) {
return true;
}
}
}
@SuppressWarnings("unchecked")
void remove(CacheDisposable<T> observer) {
for (;;) {
CacheDisposable<T>[] a = observers.get();
int n = a.length;
if (n == 0) {
return;
}
int j = -1;
for (int i = 0; i < n; i++) {
if (a[i] == observer) {
j = i;
break;
}
}
if (j < 0) {
return;
}
CacheDisposable<T>[] b;
if (n == 1) {
b = EMPTY;
} else {
b = new CacheDisposable[n - 1];
System.arraycopy(a, 0, b, 0, j);
System.arraycopy(a, j + 1, b, j, n - j - 1);
}
if (observers.compareAndSet(a, b)) {
return;
}
}
}
@Override
public void onSubscribe(Disposable d) {
boolean isDisposed;
synchronized (disposeLock) {
isDisposed = observers.get() == DISPOSED;
if (!isDisposed && observers.get() != TERMINATED) {
sourceDisposable = d;
}
}
if (isDisposed) {
d.dispose();
}
}
@SuppressWarnings("unchecked")
@Override
public void onSuccess(T value) {
this.value = value;
for (CacheDisposable<T> d : observers.getAndSet(TERMINATED)) {
if (!d.isDisposed()) {
d.actual.onSuccess(value);
}
}
}
@SuppressWarnings("unchecked")
@Override
public void onError(Throwable e) {
this.error = e;
for (CacheDisposable<T> d : observers.getAndSet(TERMINATED)) {
if (!d.isDisposed()) {
d.actual.onError(e);
}
}
}
static final class CacheDisposable<T>
extends AtomicBoolean
implements Disposable {
final SingleObserver<? super T> actual;
final DisposableSingleCache<T> parent;
CacheDisposable(SingleObserver<? super T> actual, DisposableSingleCache<T> parent) {
this.actual = actual;
this.parent = parent;
}
@Override
public boolean isDisposed() {
return get();
}
@Override
public void dispose() {
if (compareAndSet(false, true)) {
parent.remove(this);
}
}
}
}
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