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Scan backpressure and first emission fix #3171

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merged 1 commit into from
Aug 28, 2015
Merged

Scan backpressure and first emission fix #3171

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340 changes: 271 additions & 69 deletions src/main/java/rx/internal/operators/OperatorScan.java
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Original file line number Diff line number Diff line change
Expand Up @@ -15,15 +15,14 @@
*/
package rx.internal.operators;

import java.util.concurrent.atomic.AtomicBoolean;
import java.util.Queue;

import rx.*;
import rx.Observable.Operator;
import rx.Producer;
import rx.Subscriber;
import rx.exceptions.Exceptions;
import rx.exceptions.OnErrorThrowable;
import rx.functions.Func0;
import rx.functions.Func2;
import rx.exceptions.*;
import rx.functions.*;
import rx.internal.util.atomic.SpscLinkedAtomicQueue;
import rx.internal.util.unsafe.*;

/**
* Returns an Observable that applies a function to the first item emitted by a source Observable, then feeds
Expand Down Expand Up @@ -87,87 +86,290 @@ public OperatorScan(final Func2<R, ? super T, R> accumulator) {

@Override
public Subscriber<? super T> call(final Subscriber<? super R> child) {
return new Subscriber<T>(child) {
private final R initialValue = initialValueFactory.call();
final R initialValue = initialValueFactory.call();

if (initialValue == NO_INITIAL_VALUE) {
return new Subscriber<T>(child) {
boolean once;
R value;
@SuppressWarnings("unchecked")
@Override
public void onNext(T t) {
R v;
if (!once) {
once = true;
v = (R)t;
} else {
v = value;
try {
v = accumulator.call(v, t);
} catch (Throwable e) {
Exceptions.throwIfFatal(e);
child.onError(OnErrorThrowable.addValueAsLastCause(e, t));
return;
}
}
value = v;
child.onNext(v);
}
@Override
public void onError(Throwable e) {
child.onError(e);
}
@Override
public void onCompleted() {
child.onCompleted();
}
};
}

final InitialProducer<R> ip = new InitialProducer<R>(initialValue, child);

Subscriber<T> parent = new Subscriber<T>() {
private R value = initialValue;
boolean initialized = false;

@SuppressWarnings("unchecked")
@Override
public void onNext(T currentValue) {
emitInitialValueIfNeeded(child);

if (this.value == NO_INITIAL_VALUE) {
// if there is NO_INITIAL_VALUE then we know it is type T for both so cast T to R
this.value = (R) currentValue;
} else {
try {
this.value = accumulator.call(this.value, currentValue);
} catch (Throwable e) {
Exceptions.throwIfFatal(e);
child.onError(OnErrorThrowable.addValueAsLastCause(e, currentValue));
return;
}
R v = value;
try {
v = accumulator.call(v, currentValue);
} catch (Throwable e) {
Exceptions.throwIfFatal(e);
onError(OnErrorThrowable.addValueAsLastCause(e, currentValue));
return;
}
child.onNext(this.value);
value = v;
ip.onNext(v);
}

@Override
public void onError(Throwable e) {
child.onError(e);
ip.onError(e);
}

@Override
public void onCompleted() {
emitInitialValueIfNeeded(child);
child.onCompleted();
}

private void emitInitialValueIfNeeded(final Subscriber<? super R> child) {
if (!initialized) {
initialized = true;
// we emit first time through if we have an initial value
if (initialValue != NO_INITIAL_VALUE) {
child.onNext(initialValue);
}
}
ip.onCompleted();
}

/**
* We want to adjust the requested value by subtracting 1 if we have an initial value
*/
@Override
public void setProducer(final Producer producer) {
child.setProducer(new Producer() {

final AtomicBoolean once = new AtomicBoolean();

final AtomicBoolean excessive = new AtomicBoolean();

@Override
public void request(long n) {
if (once.compareAndSet(false, true)) {
if (initialValue == NO_INITIAL_VALUE || n == Long.MAX_VALUE) {
producer.request(n);
} else if (n == 1) {
excessive.set(true);
producer.request(1); // request at least 1
} else {
// n != Long.MAX_VALUE && n != 1
producer.request(n - 1);
}
} else {
// pass-thru after first time
if (n > 1 // avoid to request 0
&& excessive.compareAndSet(true, false) && n != Long.MAX_VALUE) {
producer.request(n - 1);
} else {
producer.request(n);
}
ip.setProducer(producer);
}
};

child.add(parent);
child.setProducer(ip);
return parent;
}

static final class InitialProducer<R> implements Producer, Observer<R> {
final Subscriber<? super R> child;
final Queue<Object> queue;

boolean emitting;
/** Missed a terminal event. */
boolean missed;
/** Missed a request. */
long missedRequested;
/** Missed a producer. */
Producer missedProducer;
/** The current requested amount. */
long requested;
/** The current producer. */
Producer producer;

volatile boolean done;
Throwable error;

public InitialProducer(R initialValue, Subscriber<? super R> child) {
this.child = child;
Queue<Object> q;
// TODO switch to the linked-array based queue once available
if (UnsafeAccess.isUnsafeAvailable()) {
q = new SpscLinkedQueue<Object>(); // new SpscUnboundedArrayQueue<R>(8);
} else {
q = new SpscLinkedAtomicQueue<Object>(); // new SpscUnboundedAtomicArrayQueue<R>(8);
}
this.queue = q;
q.offer(initialValue);
}

@Override
public void request(long n) {
if (n < 0L) {
throw new IllegalArgumentException("n >= required but it was " + n);
} else
if (n != 0L) {
synchronized (this) {
if (emitting) {
long mr = missedRequested;
long mu = mr + n;
if (mu < 0L) {
mu = Long.MAX_VALUE;
}
missedRequested = mu;
return;
}
});
emitting = true;
}

long r = requested;
long u = r + n;
if (u < 0L) {
u = Long.MAX_VALUE;
}
requested = u;

Producer p = producer;
if (p != null) {
p.request(n);
}

emitLoop();
}
};
}

@Override
public void onNext(R t) {
queue.offer(NotificationLite.instance().next(t));
emit();
}

boolean checkTerminated(boolean d, boolean empty, Subscriber<? super R> child) {
if (child.isUnsubscribed()) {
return true;
}
if (d) {
Throwable err = error;
if (err != null) {
child.onError(err);
return true;
} else
if (empty) {
child.onCompleted();
return true;
}
}
return false;
}

@Override
public void onError(Throwable e) {
error = e;
done = true;
emit();
}

@Override
public void onCompleted() {
done = true;
emit();
}

public void setProducer(Producer p) {
if (p == null) {
throw new NullPointerException();
}
synchronized (this) {
if (emitting) {
missedProducer = p;
return;
}
emitting = true;
}
producer = p;
long r = requested;
if (r != 0L) {
p.request(r);
}
emitLoop();
}

void emit() {
synchronized (this) {
if (emitting) {
missed = true;
return;
}
emitting = true;
}
emitLoop();
}

void emitLoop() {
final Subscriber<? super R> child = this.child;
final Queue<Object> queue = this.queue;
final NotificationLite<R> nl = NotificationLite.instance();
long r = requested;
for (;;) {
boolean max = r == Long.MAX_VALUE;
boolean d = done;
boolean empty = queue.isEmpty();
if (checkTerminated(d, empty, child)) {
return;
}
while (r != 0L) {
d = done;
Object o = queue.poll();
empty = o == null;
if (checkTerminated(d, empty, child)) {
return;
}
if (empty) {
break;
}
R v = nl.getValue(o);
try {
child.onNext(v);
} catch (Throwable e) {
Exceptions.throwIfFatal(e);
child.onError(OnErrorThrowable.addValueAsLastCause(e, v));
return;
}
if (!max) {
r--;
}
}
if (!max) {
requested = r;
}

Producer p;
long mr;
synchronized (this) {
p = missedProducer;
mr = missedRequested;
if (!missed && p == null && mr == 0L) {
emitting = false;
return;
}
missed = false;
missedProducer = null;
missedRequested = 0L;
}

if (mr != 0L && !max) {
long u = r + mr;
if (u < 0L) {
u = Long.MAX_VALUE;
}
requested = u;
r = u;
}

if (p != null) {
producer = p;
if (r != 0L) {
p.request(r);
}
} else {
p = producer;
if (p != null && mr != 0L) {
p.request(mr);
}
}
}
}
}
}
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