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core: initialize round robin load balancer picker to random index #4462

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Merged
merged 1 commit into from
Aug 1, 2018
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core: initialize round robin load balancer picker to random index #4462

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15 changes: 12 additions & 3 deletions core/src/main/java/io/grpc/util/RoundRobinLoadBalancerFactory.java
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Original file line number Diff line number Diff line change
Expand Up @@ -49,6 +49,7 @@
import java.util.Map;
import java.util.NoSuchElementException;
import java.util.Queue;
import java.util.Random;
import java.util.Set;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.ConcurrentLinkedQueue;
Expand Down Expand Up @@ -110,12 +111,14 @@ static final class RoundRobinLoadBalancer extends LoadBalancer {
private final Helper helper;
private final Map<EquivalentAddressGroup, Subchannel> subchannels =
new HashMap<EquivalentAddressGroup, Subchannel>();
private final Random random;

@Nullable
private StickinessState stickinessState;

RoundRobinLoadBalancer(Helper helper) {
this.helper = checkNotNull(helper, "helper");
this.random = new Random();
}

@Override
Expand Down Expand Up @@ -211,7 +214,12 @@ public void shutdown() {
*/
private void updateBalancingState(ConnectivityState state, Status error) {
List<Subchannel> activeList = filterNonFailingSubchannels(getSubchannels());
helper.updateBalancingState(state, new Picker(activeList, error, stickinessState));
// initialize the Picker to a random start index to ensure that a high frequency of Picker
// churn does not skew subchannel selection.
int startIndex = activeList.isEmpty() ? 0 : random.nextInt(activeList.size());
helper.updateBalancingState(
state,
new Picker(activeList, error, startIndex, stickinessState));
}

/**
Expand Down Expand Up @@ -388,14 +396,15 @@ static final class Picker extends SubchannelPicker {
@Nullable
private final RoundRobinLoadBalancer.StickinessState stickinessState;
@SuppressWarnings("unused")
private volatile int index = -1; // start off at -1 so the address on first use is 0.
private volatile int index;

Picker(
List<Subchannel> list, @Nullable Status status,
List<Subchannel> list, @Nullable Status status, int startIndex,
@Nullable RoundRobinLoadBalancer.StickinessState stickinessState) {
this.list = list;
this.status = status;
this.stickinessState = stickinessState;
this.index = startIndex - 1;
}

@Override
Expand Down
102 changes: 57 additions & 45 deletions core/src/test/java/io/grpc/util/RoundRobinLoadBalancerTest.java
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Original file line number Diff line number Diff line change
Expand Up @@ -272,14 +272,19 @@ public void pickAfterStateChange() throws Exception {
verifyNoMoreInteractions(mockHelper);
}

private Subchannel nextSubchannel(Subchannel current, List<Subchannel> allSubChannels) {
return allSubChannels.get((allSubChannels.indexOf(current) + 1) % allSubChannels.size());
}

@Test
public void pickerRoundRobin() throws Exception {
Subchannel subchannel = mock(Subchannel.class);
Subchannel subchannel1 = mock(Subchannel.class);
Subchannel subchannel2 = mock(Subchannel.class);

Picker picker = new Picker(Collections.unmodifiableList(Lists.<Subchannel>newArrayList(
subchannel, subchannel1, subchannel2)), null /* status */, null /* stickinessState */);
Picker picker = new Picker(Collections.unmodifiableList(Lists.newArrayList(
subchannel, subchannel1, subchannel2)), null /* status */, 0 /* startIndex */,
null /* stickinessState */);

assertThat(picker.getList()).containsExactly(subchannel, subchannel1, subchannel2);

Expand All @@ -292,7 +297,7 @@ public void pickerRoundRobin() throws Exception {
@Test
public void pickerEmptyList() throws Exception {
Picker picker =
new Picker(Lists.<Subchannel>newArrayList(), Status.UNKNOWN, null /* stickinessState */);
new Picker(Lists.<Subchannel>newArrayList(), Status.UNKNOWN, 0, null /* stickinessState */);

assertEquals(null, picker.pickSubchannel(mockArgs).getSubchannel());
assertEquals(Status.UNKNOWN,
Expand Down Expand Up @@ -395,14 +400,16 @@ public void noStickinessEnabled_withStickyHeader() {
headerWithStickinessValue.put(stickinessKey, "my-sticky-value");
doReturn(headerWithStickinessValue).when(mockArgs).getHeaders();

Iterator<Subchannel> subchannelIterator = loadBalancer.getSubchannels().iterator();
Subchannel sc1 = subchannelIterator.next();
Subchannel sc2 = subchannelIterator.next();
Subchannel sc3 = subchannelIterator.next();
assertEquals(sc1, picker.pickSubchannel(mockArgs).getSubchannel());
assertEquals(sc2, picker.pickSubchannel(mockArgs).getSubchannel());
assertEquals(sc3, picker.pickSubchannel(mockArgs).getSubchannel());
assertEquals(sc1, picker.pickSubchannel(mockArgs).getSubchannel());
List<Subchannel> allSubchannels = picker.getList();
Subchannel sc1 = picker.pickSubchannel(mockArgs).getSubchannel();
Subchannel sc2 = picker.pickSubchannel(mockArgs).getSubchannel();
Subchannel sc3 = picker.pickSubchannel(mockArgs).getSubchannel();
Subchannel sc4 = picker.pickSubchannel(mockArgs).getSubchannel();

assertEquals(nextSubchannel(sc1, allSubchannels), sc2);
assertEquals(nextSubchannel(sc2, allSubchannels), sc3);
assertEquals(nextSubchannel(sc3, allSubchannels), sc1);
assertEquals(sc4, sc1);

assertNull(loadBalancer.getStickinessMapForTest());
}
Expand All @@ -423,15 +430,17 @@ public void stickinessEnabled_withoutStickyHeader() {

doReturn(new Metadata()).when(mockArgs).getHeaders();

Iterator<Subchannel> subchannelIterator = loadBalancer.getSubchannels().iterator();
Subchannel sc1 = subchannelIterator.next();
Subchannel sc2 = subchannelIterator.next();
Subchannel sc3 = subchannelIterator.next();
assertEquals(sc1, picker.pickSubchannel(mockArgs).getSubchannel());
assertEquals(sc2, picker.pickSubchannel(mockArgs).getSubchannel());
assertEquals(sc3, picker.pickSubchannel(mockArgs).getSubchannel());
assertEquals(sc1, picker.pickSubchannel(mockArgs).getSubchannel());
List<Subchannel> allSubchannels = picker.getList();

Subchannel sc1 = picker.pickSubchannel(mockArgs).getSubchannel();
Subchannel sc2 = picker.pickSubchannel(mockArgs).getSubchannel();
Subchannel sc3 = picker.pickSubchannel(mockArgs).getSubchannel();
Subchannel sc4 = picker.pickSubchannel(mockArgs).getSubchannel();

assertEquals(nextSubchannel(sc1, allSubchannels), sc2);
assertEquals(nextSubchannel(sc2, allSubchannels), sc3);
assertEquals(nextSubchannel(sc3, allSubchannels), sc1);
assertEquals(sc4, sc1);
verify(mockArgs, times(4)).getHeaders();
assertNotNull(loadBalancer.getStickinessMapForTest());
assertThat(loadBalancer.getStickinessMapForTest()).isEmpty();
Expand All @@ -456,7 +465,7 @@ public void stickinessEnabled_withStickyHeader() {
headerWithStickinessValue.put(stickinessKey, "my-sticky-value");
doReturn(headerWithStickinessValue).when(mockArgs).getHeaders();

Subchannel sc1 = loadBalancer.getSubchannels().iterator().next();
Subchannel sc1 = picker.pickSubchannel(mockArgs).getSubchannel();
assertEquals(sc1, picker.pickSubchannel(mockArgs).getSubchannel());
assertEquals(sc1, picker.pickSubchannel(mockArgs).getSubchannel());
assertEquals(sc1, picker.pickSubchannel(mockArgs).getSubchannel());
Expand Down Expand Up @@ -488,21 +497,24 @@ public void stickinessEnabled_withDifferentStickyHeaders() {
Metadata headerWithStickinessValue2 = new Metadata();
headerWithStickinessValue2.put(stickinessKey, "my-sticky-value2");

Iterator<Subchannel> subchannelIterator = loadBalancer.getSubchannels().iterator();
Subchannel sc1 = subchannelIterator.next();
Subchannel sc2 = subchannelIterator.next();
List<Subchannel> allSubchannels = picker.getList();

doReturn(headerWithStickinessValue1).when(mockArgs).getHeaders();
assertEquals(sc1, picker.pickSubchannel(mockArgs).getSubchannel());
Subchannel sc1a = picker.pickSubchannel(mockArgs).getSubchannel();

doReturn(headerWithStickinessValue2).when(mockArgs).getHeaders();
assertEquals(sc2, picker.pickSubchannel(mockArgs).getSubchannel());
Subchannel sc2a = picker.pickSubchannel(mockArgs).getSubchannel();

doReturn(headerWithStickinessValue1).when(mockArgs).getHeaders();
assertEquals(sc1, picker.pickSubchannel(mockArgs).getSubchannel());
Subchannel sc1b = picker.pickSubchannel(mockArgs).getSubchannel();

doReturn(headerWithStickinessValue2).when(mockArgs).getHeaders();
assertEquals(sc2, picker.pickSubchannel(mockArgs).getSubchannel());
Subchannel sc2b = picker.pickSubchannel(mockArgs).getSubchannel();

assertEquals(sc1a, sc1b);
assertEquals(sc2a, sc2b);
assertEquals(nextSubchannel(sc1a, allSubchannels), sc2a);
assertEquals(nextSubchannel(sc1b, allSubchannels), sc2b);

verify(mockArgs, atLeast(4)).getHeaders();
assertNotNull(loadBalancer.getStickinessMapForTest());
Expand All @@ -528,12 +540,10 @@ public void stickiness_goToTransientFailure_pick_backToReady() {
headerWithStickinessValue.put(stickinessKey, "my-sticky-value");
doReturn(headerWithStickinessValue).when(mockArgs).getHeaders();

Iterator<Subchannel> subchannelIterator = loadBalancer.getSubchannels().iterator();
Subchannel sc1 = subchannelIterator.next();
Subchannel sc2 = subchannelIterator.next();
List<Subchannel> allSubchannels = picker.getList();

// first pick
assertEquals(sc1, picker.pickSubchannel(mockArgs).getSubchannel());
Subchannel sc1 = picker.pickSubchannel(mockArgs).getSubchannel();

// go to transient failure
loadBalancer
Expand All @@ -542,18 +552,20 @@ public void stickiness_goToTransientFailure_pick_backToReady() {
verify(mockHelper, times(5))
.updateBalancingState(stateCaptor.capture(), pickerCaptor.capture());
picker = pickerCaptor.getValue();

// second pick
assertEquals(sc2, picker.pickSubchannel(mockArgs).getSubchannel());
Subchannel sc2 = picker.pickSubchannel(mockArgs).getSubchannel();

// go back to ready
loadBalancer.handleSubchannelState(sc1, ConnectivityStateInfo.forNonError(READY));

verify(mockHelper, times(6))
.updateBalancingState(stateCaptor.capture(), pickerCaptor.capture());
picker = pickerCaptor.getValue();
// third pick
assertEquals(sc2, picker.pickSubchannel(mockArgs).getSubchannel());

// third pick
Subchannel sc3 = picker.pickSubchannel(mockArgs).getSubchannel();
assertEquals(sc2, sc3);
verify(mockArgs, atLeast(3)).getHeaders();
assertNotNull(loadBalancer.getStickinessMapForTest());
assertThat(loadBalancer.getStickinessMapForTest()).hasSize(1);
Expand All @@ -578,12 +590,10 @@ public void stickiness_goToTransientFailure_backToReady_pick() {
headerWithStickinessValue1.put(stickinessKey, "my-sticky-value");
doReturn(headerWithStickinessValue1).when(mockArgs).getHeaders();

Iterator<Subchannel> subchannelIterator = loadBalancer.getSubchannels().iterator();
Subchannel sc1 = subchannelIterator.next();
Subchannel sc2 = subchannelIterator.next();
List<Subchannel> allSubchannels = picker.getList();

// first pick
assertEquals(sc1, picker.pickSubchannel(mockArgs).getSubchannel());
Subchannel sc1 = picker.pickSubchannel(mockArgs).getSubchannel();

// go to transient failure
loadBalancer
Expand All @@ -595,8 +605,9 @@ public void stickiness_goToTransientFailure_backToReady_pick() {
verify(mockHelper, times(5))
.updateBalancingState(stateCaptor.capture(), pickerCaptor.capture());
picker = pickerCaptor.getValue();

// second pick with a different stickiness value
assertEquals(sc2, picker.pickSubchannel(mockArgs).getSubchannel());
Subchannel sc2 = picker.pickSubchannel(mockArgs).getSubchannel();

// go back to ready
loadBalancer.handleSubchannelState(sc1, ConnectivityStateInfo.forNonError(READY));
Expand All @@ -605,8 +616,10 @@ public void stickiness_goToTransientFailure_backToReady_pick() {
verify(mockHelper, times(6))
.updateBalancingState(stateCaptor.capture(), pickerCaptor.capture());
picker = pickerCaptor.getValue();

// third pick with my-sticky-value1
assertEquals(sc1, picker.pickSubchannel(mockArgs).getSubchannel());
Subchannel sc3 = picker.pickSubchannel(mockArgs).getSubchannel();
assertEquals(sc1, sc3);

verify(mockArgs, atLeast(3)).getHeaders();
assertNotNull(loadBalancer.getStickinessMapForTest());
Expand All @@ -632,18 +645,17 @@ public void stickiness_oneSubchannelShutdown() {
headerWithStickinessValue.put(stickinessKey, "my-sticky-value");
doReturn(headerWithStickinessValue).when(mockArgs).getHeaders();

Iterator<Subchannel> subchannelIterator = loadBalancer.getSubchannels().iterator();
Subchannel sc1 = subchannelIterator.next();
Subchannel sc2 = subchannelIterator.next();
List<Subchannel> allSubchannels = Lists.newArrayList(picker.getList());

assertEquals(sc1, picker.pickSubchannel(mockArgs).getSubchannel());
Subchannel sc1 = picker.pickSubchannel(mockArgs).getSubchannel();

loadBalancer
.handleSubchannelState(sc1, ConnectivityStateInfo.forNonError(ConnectivityState.SHUTDOWN));

assertNull(loadBalancer.getStickinessMapForTest().get("my-sticky-value").value);

assertEquals(sc2, picker.pickSubchannel(mockArgs).getSubchannel());
assertEquals(nextSubchannel(sc1, allSubchannels),
picker.pickSubchannel(mockArgs).getSubchannel());
assertThat(loadBalancer.getStickinessMapForTest()).hasSize(1);
verify(mockArgs, atLeast(2)).getHeaders();
}
Expand Down