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Added latch to async SyncOnSubscrbeTest #3285

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Merged
merged 1 commit into from
Sep 4, 2015
Merged

Added latch to async SyncOnSubscrbeTest #3285

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74 changes: 41 additions & 33 deletions src/main/java/rx/observables/SyncOnSubscribe.java
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Original file line number Diff line number Diff line change
Expand Up @@ -16,7 +16,6 @@

package rx.observables;

import java.util.concurrent.atomic.AtomicIntegerFieldUpdater;
import java.util.concurrent.atomic.AtomicLong;

import rx.Observable.OnSubscribe;
Expand Down Expand Up @@ -321,14 +320,9 @@ private static class SubscriptionProducer<S, T>
private final SyncOnSubscribe<S, T> parent;
private boolean onNextCalled;
private boolean hasTerminated;

private S state;

volatile int isUnsubscribed;
@SuppressWarnings("rawtypes")
static final AtomicIntegerFieldUpdater<SubscriptionProducer> IS_UNSUBSCRIBED =
AtomicIntegerFieldUpdater.newUpdater(SubscriptionProducer.class, "isUnsubscribed");

private SubscriptionProducer(final Subscriber<? super T> subscriber, SyncOnSubscribe<S, T> parent, S state) {
this.actualSubscriber = subscriber;
this.parent = parent;
Expand All @@ -337,14 +331,39 @@ private SubscriptionProducer(final Subscriber<? super T> subscriber, SyncOnSubsc

@Override
public boolean isUnsubscribed() {
return isUnsubscribed != 0;
return get() < 0L;
}

@Override
public void unsubscribe() {
IS_UNSUBSCRIBED.compareAndSet(this, 0, 1);
if (get() == 0L)
parent.onUnsubscribe(state);
while(true) {
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There is a much simpler way of fixing this: undo all these latest changes and request 1!

if (BackpressureUtils.getAndAddRequest(this, 1) == 0) {
    parent.onUnsubscribe(state);
}

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It's interesting. If there is currently a thread processing over the request count loop (i.e. processing nextIteration()) then won't this have to block the unsubscribing thread? The unsubscribing thread would have to poll over this until it got access. I'm not seeing how this would force a thread currently iterating to terminate. If you read through the concurrency I think you will see that it's not really all that complicated and I believe it sufficiently covers the possible race conditions.

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There is no blocking. My suggestion follows the queue-drain approach where you queue the terminal flag and drain it in the emission loop. Since the loop first checks for the terminal flag there won't be any wrong emissions and the loop quits. If unsubscribe increments from zero, there isn't and won't be any emission loop after that and the resource can be freed.

There is no need for your complicated solution.

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I'm not seeing where you are suggesting setting a terminal flag. You are more than welcome to open your own pull request to demonstrate your fix. My pull request does set a flag for the draining thread to signal when it needs to unsubscribe.

long requestCount = get();
if (compareAndSet(0L, -1L)) {
doUnsubscribe();
return;
}
else if (compareAndSet(requestCount, -2L))
// the loop is iterating concurrently
// need to check if requestCount == -1
// and unsub if so after loop iteration
return;
}
}

private boolean tryUnsubscribe() {
// only one thread at a time can iterate over request count
// therefore the requestCount atomic cannot be decrement concurrently here
// safe to set to -1 atomically (since this check can only be done by 1 thread)
if (hasTerminated || get() < -1) {
set(-1);
doUnsubscribe();
return true;
}
return false;
}

private void doUnsubscribe() {
parent.onUnsubscribe(state);
}

@Override
Expand All @@ -358,71 +377,60 @@ public void request(long n) {
}
}

void fastpath() {
private void fastpath() {
final SyncOnSubscribe<S, T> p = parent;
Subscriber<? super T> a = actualSubscriber;

if (isUnsubscribed()) {
p.onUnsubscribe(state);
return;
}

for (;;) {
try {
onNextCalled = false;
nextIteration(p);
} catch (Throwable ex) {
handleThrownError(p, a, state, ex);
handleThrownError(a, ex);
return;
}
if (hasTerminated || isUnsubscribed()) {
p.onUnsubscribe(state);
if (tryUnsubscribe()) {
return;
}
}
}

private void handleThrownError(final SyncOnSubscribe<S, T> p, Subscriber<? super T> a, S st, Throwable ex) {
private void handleThrownError(Subscriber<? super T> a, Throwable ex) {
if (hasTerminated) {
RxJavaPlugins.getInstance().getErrorHandler().handleError(ex);
} else {
hasTerminated = true;
a.onError(ex);
p.onUnsubscribe(st);
unsubscribe();
}
}

void slowPath(long n) {
private void slowPath(long n) {
final SyncOnSubscribe<S, T> p = parent;
Subscriber<? super T> a = actualSubscriber;
long numRequested = n;
for (;;) {
if (isUnsubscribed()) {
p.onUnsubscribe(state);
return;
}
long numRemaining = numRequested;
do {
try {
onNextCalled = false;
nextIteration(p);
} catch (Throwable ex) {
handleThrownError(p, a, state, ex);
handleThrownError(a, ex);
return;
}
if (hasTerminated || isUnsubscribed()) {
p.onUnsubscribe(state);
if (tryUnsubscribe()) {
return;
}
if (onNextCalled)
numRemaining--;
} while (numRemaining != 0L);

numRequested = addAndGet(-numRequested);
if (numRequested == 0L) {
if (numRequested <= 0L)
break;
}
}
// catches cases where unsubscribe is called before decrementing atomic request count
tryUnsubscribe();
}

private void nextIteration(final SyncOnSubscribe<S, T> parent) {
Expand Down
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