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2.x: fix scan(seed, f) to emit accumulated values asap #5090

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Feb 11, 2017
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2.x: fix scan(seed, f) to emit accumulated values asap #5090

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174 changes: 154 additions & 20 deletions src/main/java/io/reactivex/internal/operators/flowable/FlowableScanSeed.java
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Original file line number Diff line number Diff line change
Expand Up @@ -13,14 +13,17 @@
package io.reactivex.internal.operators.flowable;

import java.util.concurrent.Callable;
import java.util.concurrent.atomic.*;

import org.reactivestreams.*;

import io.reactivex.exceptions.Exceptions;
import io.reactivex.functions.BiFunction;
import io.reactivex.internal.functions.ObjectHelper;
import io.reactivex.internal.subscribers.SinglePostCompleteSubscriber;
import io.reactivex.internal.subscriptions.EmptySubscription;
import io.reactivex.internal.fuseable.SimplePlainQueue;
import io.reactivex.internal.queue.SpscArrayQueue;
import io.reactivex.internal.subscriptions.*;
import io.reactivex.internal.util.BackpressureHelper;
import io.reactivex.plugins.RxJavaPlugins;

public final class FlowableScanSeed<T, R> extends AbstractFlowableWithUpstream<T, R> {
Expand All @@ -45,20 +48,57 @@ protected void subscribeActual(Subscriber<? super R> s) {
return;
}

source.subscribe(new ScanSeedSubscriber<T, R>(s, accumulator, r));
source.subscribe(new ScanSeedSubscriber<T, R>(s, accumulator, r, bufferSize()));
}

static final class ScanSeedSubscriber<T, R> extends SinglePostCompleteSubscriber<T, R> {
static final class ScanSeedSubscriber<T, R>
extends AtomicInteger
implements Subscriber<T>, Subscription {
private static final long serialVersionUID = -1776795561228106469L;

final Subscriber<? super R> actual;

final BiFunction<R, ? super T, R> accumulator;

boolean done;
final SimplePlainQueue<R> queue;

final AtomicLong requested;

final int prefetch;

final int limit;

volatile boolean cancelled;

volatile boolean done;
Throwable error;

Subscription s;

R value;

ScanSeedSubscriber(Subscriber<? super R> actual, BiFunction<R, ? super T, R> accumulator, R value) {
super(actual);
int consumed;

ScanSeedSubscriber(Subscriber<? super R> actual, BiFunction<R, ? super T, R> accumulator, R value, int prefetch) {
this.actual = actual;
this.accumulator = accumulator;
this.value = value;
this.prefetch = prefetch;
this.limit = prefetch - (prefetch >> 2);
this.queue = new SpscArrayQueue<R>(prefetch);
this.queue.offer(value);
this.requested = new AtomicLong();
}

@Override
public void onSubscribe(Subscription s) {
if (SubscriptionHelper.validate(this.s, s)) {
this.s = s;

actual.onSubscribe(this);

s.request(prefetch - 1);
}
}

@Override
Expand All @@ -68,21 +108,18 @@ public void onNext(T t) {
}

R v = value;

R u;

try {
u = ObjectHelper.requireNonNull(accumulator.apply(v, t), "The accumulator returned a null value");
} catch (Throwable e) {
Exceptions.throwIfFatal(e);
v = ObjectHelper.requireNonNull(accumulator.apply(v, t), "The accumulator returned a null value");
} catch (Throwable ex) {
Exceptions.throwIfFatal(ex);
s.cancel();
onError(e);
onError(ex);
return;
}

value = u;
produced++;
actual.onNext(v);
value = v;
queue.offer(v);
drain();
}

@Override
Expand All @@ -91,9 +128,9 @@ public void onError(Throwable t) {
RxJavaPlugins.onError(t);
return;
}
error = t;
done = true;
value = null;
actual.onError(t);
drain();
}

@Override
Expand All @@ -102,7 +139,104 @@ public void onComplete() {
return;
}
done = true;
complete(value);
drain();
}

@Override
public void cancel() {
cancelled = true;
s.cancel();
if (getAndIncrement() == 0) {
queue.clear();
}
}

@Override
public void request(long n) {
if (SubscriptionHelper.validate(n)) {
BackpressureHelper.add(requested, n);
drain();
}
}

void drain() {
if (getAndIncrement() != 0) {
return;
}

int missed = 1;
Subscriber<? super R> a = actual;
SimplePlainQueue<R> q = queue;
int lim = limit;
int c = consumed;

for (;;) {

long r = requested.get();
long e = 0L;

while (e != r) {
if (cancelled) {
q.clear();
return;
}
boolean d = done;

if (d) {
Throwable ex = error;
if (ex != null) {
q.clear();
a.onError(ex);
return;
}
}

R v = q.poll();
boolean empty = v == null;

if (d && empty) {
a.onComplete();
return;
}

if (empty) {
break;
}

a.onNext(v);

e++;
if (++c == lim) {
c = 0;
s.request(lim);
}
}

if (e == r) {
if (done) {
Throwable ex = error;
if (ex != null) {
q.clear();
a.onError(ex);
return;
}
if (q.isEmpty()) {
a.onComplete();
return;
}
}
}

if (e != 0L) {
BackpressureHelper.produced(requested, e);
}

consumed = c;
missed = addAndGet(-missed);
if (missed == 0) {
break;
}
}
}
}
}
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