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Multi discrepancies #2413

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merged 3 commits into from Oct 7, 2020
Merged

Multi discrepancies #2413

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b9c346f
Multi discrepancies
danielkec Oct 6, 2020
693ad01
Review issues
danielkec Oct 6, 2020
d3cb64c
Revert concat array changes
danielkec Oct 7, 2020
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118 changes: 41 additions & 77 deletions common/reactive/src/main/java/io/helidon/common/reactive/DeferredScalarSubscription.java
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Expand Up @@ -23,6 +23,7 @@

/**
* Buffers a single item and emits it to the downstream when it requests.
*
* @param <T> the item type buffered
*/
class DeferredScalarSubscription<T> extends AtomicInteger implements Flow.Subscription {
Expand All @@ -31,91 +32,66 @@ class DeferredScalarSubscription<T> extends AtomicInteger implements Flow.Subscr

private T value;

static final int NO_VALUE_NO_REQUEST = 0;
static final int NO_VALUE_HAS_REQUEST = 1;
static final int HAS_VALUE_NO_REQUEST = 2;
static final int HAS_VALUE_HAS_REQUEST = 3;
static final int COMPLETE = 4;
static final int CANCELED = 5;
static final int REQUEST_ARRIVED = 1;
static final int VALUE_ARRIVED = 2;
static final int DONE = REQUEST_ARRIVED | VALUE_ARRIVED;


DeferredScalarSubscription(Flow.Subscriber<? super T> downstream) {
this.downstream = downstream;
}

@Override
public void cancel() {
if (getAndSet(CANCELED) != CANCELED) {
if (getAndSet(DONE) != DONE) {
value = null;
}
}

@Override
public final void request(long n) {
if (n <= 0L) {
if (getAndSet(CANCELED) != CANCELED) {
if (getAndSet(DONE) != DONE) {
value = null;
downstream.onError(
new IllegalArgumentException("Rule §3.9 violated: non-positive requests are forbidden"));
}
} else {
for (;;) {
int state = get();
if (state == HAS_VALUE_NO_REQUEST) {
T v = value;
value = null;
if (compareAndSet(HAS_VALUE_NO_REQUEST, HAS_VALUE_HAS_REQUEST)) {
downstream.onNext(v);
if (compareAndSet(HAS_VALUE_HAS_REQUEST, COMPLETE)) {
downstream.onComplete();
}
break;
}
} else if (state == NO_VALUE_NO_REQUEST) {
if (compareAndSet(NO_VALUE_NO_REQUEST, NO_VALUE_HAS_REQUEST)) {
break;
}
} else {
// state == COMPLETE
// state == HAS_VALUE_HAS_REQUEST
// state == NO_VALUE_HAS_REQUEST
// state == CANCELED
break;
}
}
return;
}

int state;
T v;
do {
state = get();
v = value;
} while (!compareAndSet(state, state | REQUEST_ARRIVED));

if (state == VALUE_ARRIVED) {
value = null;
downstream.onNext(v);
downstream.onComplete();
}
}

/**
* Signal the only item if possible or save it for later when there
* is a request for it.
* <p>
* This method should be called at most once and from only one thread.
* This method should be called at most once and from only one thread.
* </p>
*
* @param item the item to signal and then complete the downstream
*/
public final void complete(T item) {
for (;;) {
int state = get();
if (state == NO_VALUE_HAS_REQUEST) {
if (compareAndSet(NO_VALUE_HAS_REQUEST, HAS_VALUE_HAS_REQUEST)) {
downstream.onNext(item);
if (compareAndSet(HAS_VALUE_HAS_REQUEST, COMPLETE)) {
downstream.onComplete();
}
break;
}
} else if (state == NO_VALUE_NO_REQUEST) {
value = item;
if (compareAndSet(NO_VALUE_NO_REQUEST, HAS_VALUE_NO_REQUEST)) {
break;
}
value = null;
} else {
// state == COMPLETE
// state == HAS_VALUE_NO_REQUEST
// state == HAS_VALUE_HAS_REQUEST
// state == CANCELED
break;
}
value = item; // assert: even if the race occurs, we will deliver one of the items with which complete()
// has been invoked - we support only the case with a single invocation of complete()
int state = getAndUpdate(n -> n | VALUE_ARRIVED);
if (state == REQUEST_ARRIVED) {
value = null;
downstream.onNext(item);
downstream.onComplete();
} else if (state == DONE) {
value = null;
}
}

Expand All @@ -128,6 +104,7 @@ protected final void subscribeSelf() {

/**
* Returns the downstream reference.
*
* @return the downstream reference
*/
protected final Flow.Subscriber<? super T> downstream() {
Expand All @@ -138,34 +115,21 @@ protected final Flow.Subscriber<? super T> downstream() {
* Complete the downstream without emitting any items.
*/
public final void complete() {
for (;;) {
int state = get();
if (state == NO_VALUE_NO_REQUEST || state == NO_VALUE_HAS_REQUEST) {
if (compareAndSet(state, COMPLETE)) {
downstream.onComplete();
return;
}
} else {
break;
}
int state = get();
if (((state & VALUE_ARRIVED) != VALUE_ARRIVED) && compareAndSet(state, DONE)){
downstream.onComplete();
}
}

/**
* Signal error to the downstream without emitting any items.
*
* @param throwable the error to signal
*/
public final void error(Throwable throwable) {
for (;;) {
int state = get();
if (state == NO_VALUE_NO_REQUEST || state == NO_VALUE_HAS_REQUEST) {
if (compareAndSet(state, COMPLETE)) {
downstream.onError(throwable);
return;
}
} else {
break;
}
if (getAndSet(DONE) != DONE) {
value = null;
downstream.onError(throwable);
}
}

Expand Down
3 changes: 2 additions & 1 deletion common/reactive/src/main/java/io/helidon/common/reactive/MultiConcatArray.java
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Expand Up @@ -39,7 +39,7 @@ public void subscribe(Flow.Subscriber<? super T> subscriber) {
}

static final class ConcatArraySubscriber<T> extends SubscriptionArbiter
implements Flow.Subscriber<T> {
implements Flow.Subscriber<T> {

private final Flow.Subscriber<? super T> downstream;

Expand Down Expand Up @@ -98,6 +98,7 @@ public void nextSource() {
@Override
public void request(long n) {
if (n <= 0) {
cancel();
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This is not sufficient for the problem that has been discovered. We'll have to address it better.

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@olotenko To be clear, your point is that the sequence onError onNext is still possible as cancellation is only a best-effort task.

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Yes, you can view this as the best effort so far. But like I mentioned offline, there is another issue that needs addressing, so we may just as well postpone touching this class.

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I see, sounds like for a future PR.

downstream.onError(new IllegalArgumentException("Rule §3.9 violated: non-positive requests are forbidden"));
} else {
super.request(n);
Expand Down
27 changes: 21 additions & 6 deletions common/reactive/src/test/java/io/helidon/common/reactive/MultiConcatArrayTest.java
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Expand Up @@ -15,14 +15,14 @@
*/
package io.helidon.common.reactive;

import org.junit.jupiter.api.Test;

import java.io.IOException;
import java.util.Arrays;
import java.util.concurrent.CompletableFuture;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.TimeoutException;

import static org.hamcrest.MatcherAssert.assertThat;
import static org.hamcrest.core.Is.is;
import static org.hamcrest.core.IsInstanceOf.instanceOf;
import org.junit.jupiter.api.Test;

public class MultiConcatArrayTest {

Expand All @@ -31,11 +31,26 @@ public void errors() {
TestSubscriber<Object> ts = new TestSubscriber<>(Long.MAX_VALUE);

Multi.concatArray(Multi.singleton(1), Multi.error(new IOException()), Multi.singleton(2))
.subscribe(ts);
.subscribe(ts);

ts.assertFailure(IOException.class, 1);
}

@Test
public void cancelOnNegativeNumberTest() throws InterruptedException, TimeoutException, ExecutionException {
TestSubscriber<Integer> ts = new TestSubscriber<>();

CompletableFuture<Void> cancelled = new CompletableFuture<>();

Multi.concatArray(Multi.just(1, 2).onCancel(() -> cancelled.complete(null)), Multi.just(3, 4))
.subscribe(ts);
ts.request(1);
ts.getSubcription().request(-1);

cancelled.get(200, TimeUnit.MILLISECONDS);
ts.assertFailure(IllegalArgumentException.class, 1);
}

@Test
public void millionSources() {
@SuppressWarnings("unchecked")
Expand Down