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Use lock free strategy for several Subscription implementations #568

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merged 9 commits into from
Dec 8, 2013
Merged

Use lock free strategy for several Subscription implementations #568

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d1706bc
Use lock free strategy
jloisel Dec 5, 2013
c728d77
Make unsubscribe + reference modification an atomic operation
jloisel Dec 5, 2013
9897ca8
Lock free strategy using a sentinel (Thanks to akarnokd)
jloisel Dec 5, 2013
d7bd826
Code simplification
jloisel Dec 5, 2013
dba41f0
Simplify code; Junits
jloisel Dec 5, 2013
ec9bd2c
fix: getSubscription should not expose internal sentinel subscription
jloisel Dec 5, 2013
39b9787
JUnit setting subscription concurrently
jloisel Dec 5, 2013
61aea25
Return null on getSubscription() when previously unsubscribed to match
jloisel Dec 6, 2013
078b687
use non-locking state machine based on atomic reference
jloisel Dec 8, 2013
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63 changes: 23 additions & 40 deletions rxjava-core/src/main/java/rx/subscriptions/SerialSubscription.java
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Original file line number Diff line number Diff line change
Expand Up @@ -15,6 +15,11 @@
*/
package rx.subscriptions;

import static rx.subscriptions.Subscriptions.empty;

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

import rx.Subscription;

/**
Expand All @@ -24,47 +29,25 @@
* @see <a href="http://msdn.microsoft.com/en-us/library/system.reactive.disposables.serialdisposable(v=vs.103).aspx">Rx.Net equivalent SerialDisposable</a>
*/
public class SerialSubscription implements Subscription {
private boolean unsubscribed;
private Subscription subscription;
private final Object gate = new Object();
private final AtomicBoolean unsubscribed = new AtomicBoolean();
private final AtomicReference<Subscription> reference = new AtomicReference<Subscription>(empty());

@Override
public void unsubscribe() {
Subscription toUnsubscribe = null;
synchronized (gate) {
if (!unsubscribed) {
if (subscription != null) {
toUnsubscribe = subscription;
subscription = null;
}
unsubscribed = true;
}
}
if (toUnsubscribe != null) {
toUnsubscribe.unsubscribe();
}
}
@Override
public void unsubscribe() {
if (unsubscribed.compareAndSet(false, true)) {
reference.getAndSet(empty()).unsubscribe();
}
}

public Subscription getSubscription() {
synchronized (gate) {
return subscription;
}
}
public void setSubscription(final Subscription subscription) {
if (unsubscribed.get()) {
subscription.unsubscribe();
} else {
reference.getAndSet(subscription == null ? empty() : subscription).unsubscribe();
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Why need to check subscription == null? I think subscription should not be null.

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Assume that we have two threads, one is calling unsubscribe, another is calling setSubscription. If the order is line 43 37 38 46, the subscription sent to setSubscription will not be unsubscribed.

}
}

public void setSubscription(Subscription subscription) {
Subscription toUnsubscribe = null;
synchronized (gate) {
if (!unsubscribed) {
if (this.subscription != null) {
toUnsubscribe = this.subscription;
}
this.subscription = subscription;
} else {
toUnsubscribe = subscription;
}
}
if (toUnsubscribe != null) {
toUnsubscribe.unsubscribe();
}
}
public Subscription getSubscription() {
return reference.get();
}
}
147 changes: 97 additions & 50 deletions rxjava-core/src/test/java/rx/subscriptions/SerialSubscriptionTests.java
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Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -15,7 +15,13 @@
*/
package rx.subscriptions;

import static org.mockito.Mockito.*;
import static org.junit.Assert.fail;
import static org.mockito.Mockito.mock;
import static org.mockito.Mockito.verify;

import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.CountDownLatch;

import org.junit.Before;
import org.junit.Test;
Expand All @@ -24,53 +30,94 @@
import rx.Subscription;

public class SerialSubscriptionTests {
private SerialSubscription serialSubscription;

@Before
public void setUp() {
MockitoAnnotations.initMocks(this);

serialSubscription = new SerialSubscription();
}

@Test
public void unsubscribingWithoutUnderlyingDoesNothing() {
serialSubscription.unsubscribe();
}

@Test
public void unsubscribingWithSingleUnderlyingUnsubscribes() {
Subscription underlying = mock(Subscription.class);
serialSubscription.setSubscription(underlying);
underlying.unsubscribe();
verify(underlying).unsubscribe();
}

@Test
public void replacingFirstUnderlyingCausesUnsubscription() {
Subscription first = mock(Subscription.class);
serialSubscription.setSubscription(first);
Subscription second = mock(Subscription.class);
serialSubscription.setSubscription(second);
verify(first).unsubscribe();
}

@Test
public void whenUnsubscribingSecondUnderlyingUnsubscribed() {
Subscription first = mock(Subscription.class);
serialSubscription.setSubscription(first);
Subscription second = mock(Subscription.class);
serialSubscription.setSubscription(second);
serialSubscription.unsubscribe();
verify(second).unsubscribe();
}

@Test
public void settingUnderlyingWhenUnsubscribedCausesImmediateUnsubscription()
{
serialSubscription.unsubscribe();
Subscription underlying = mock(Subscription.class);
serialSubscription.setSubscription(underlying);
verify(underlying).unsubscribe();
}
private SerialSubscription serialSubscription;

@Before
public void setUp() {
MockitoAnnotations.initMocks(this);

serialSubscription = new SerialSubscription();
}

@Test
public void unsubscribingWithoutUnderlyingDoesNothing() {
serialSubscription.unsubscribe();
}

@Test
public void unsubscribingWithSingleUnderlyingUnsubscribes() {
Subscription underlying = mock(Subscription.class);
serialSubscription.setSubscription(underlying);
underlying.unsubscribe();
verify(underlying).unsubscribe();
}

@Test
public void replacingFirstUnderlyingCausesUnsubscription() {
Subscription first = mock(Subscription.class);
serialSubscription.setSubscription(first);
Subscription second = mock(Subscription.class);
serialSubscription.setSubscription(second);
verify(first).unsubscribe();
}

@Test
public void whenUnsubscribingSecondUnderlyingUnsubscribed() {
Subscription first = mock(Subscription.class);
serialSubscription.setSubscription(first);
Subscription second = mock(Subscription.class);
serialSubscription.setSubscription(second);
serialSubscription.unsubscribe();
verify(second).unsubscribe();
}

@Test
public void settingUnderlyingWhenUnsubscribedCausesImmediateUnsubscription() {
serialSubscription.unsubscribe();
Subscription underlying = mock(Subscription.class);
serialSubscription.setSubscription(underlying);
verify(underlying).unsubscribe();
}

@Test(timeout = 1000)
public void settingUnderlyingWhenUnsubscribedCausesImmediateUnsubscriptionConcurrently()
throws InterruptedException {
final Subscription firstSet = mock(Subscription.class);
serialSubscription.setSubscription(firstSet);

final CountDownLatch start = new CountDownLatch(1);

final int count = 10;
final CountDownLatch end = new CountDownLatch(count);

final List<Thread> threads = new ArrayList<Thread>();
for (int i = 0 ; i < count ; i++) {
final Thread t = new Thread() {
@Override
public void run() {
try {
start.await();
serialSubscription.unsubscribe();
} catch (InterruptedException e) {
fail(e.getMessage());
} finally {
end.countDown();
}
}
};
t.start();
threads.add(t);
}

final Subscription underlying = mock(Subscription.class);
start.countDown();
serialSubscription.setSubscription(underlying);
end.await();
verify(firstSet).unsubscribe();
verify(underlying).unsubscribe();

for (final Thread t : threads) {
t.interrupt();
}
}
}