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fix: Fall back from a silent FDv2 synchronizer before data has been received #237

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fix: Fall back from a silent FDv2 synchronizer before data has been received #237

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3 changes: 0 additions & 3 deletions lib/sdk/server/contract-tests/test-suppressions-fdv2.txt
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Original file line number Diff line number Diff line change
@@ -1,3 +0,0 @@
streaming/fdv2/recoverable fallback to secondary synchronizer
streaming/fdv2/recoverable fallback with recovery
streaming/fdv2/permanent fallback with recovery
43 changes: 40 additions & 3 deletions lib/sdk/server/src/main/java/com/launchdarkly/sdk/server/FDv2DataSource.java
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Expand Up @@ -37,6 +37,12 @@ class FDv2DataSource implements DataSource {
*/
private static final long defaultRecoveryTimeout = 5 * 60;

/**
* Default time to wait for a synchronizer to deliver data, before any data has been applied, before falling back
* to the next synchronizer. The timeout is only configurable for testing.
*/
private static final long defaultInitializationFallbackTimeoutSeconds = 10;

private final SourceManager sourceManager;

private final List<ConditionFactory> conditionFactories;
Expand All @@ -45,6 +51,7 @@ class FDv2DataSource implements DataSource {

private final CompletableFuture<Boolean> startFuture = new CompletableFuture<>();
private final AtomicBoolean started = new AtomicBoolean(false);
private final AtomicBoolean dataApplied = new AtomicBoolean(false);

private final int threadPriority;

Expand Down Expand Up @@ -94,6 +101,31 @@ public FDv2DataSource(
ScheduledExecutorService sharedExecutor,
long fallbackTimeout,
long recoveryTimeout
) {
this(initializers,
synchronizers,
fdv1DataSourceFactory,
dataSourceUpdates,
threadPriority,
logger,
sharedExecutor,
fallbackTimeout,
recoveryTimeout,
defaultInitializationFallbackTimeoutSeconds
);
}

public FDv2DataSource(
ImmutableList<DataSourceFactory<Initializer>> initializers,
ImmutableList<DataSourceFactory<Synchronizer>> synchronizers,
DataSourceFactory<Synchronizer> fdv1DataSourceFactory,
DataSourceUpdateSinkV2 dataSourceUpdates,
int threadPriority,
LDLogger logger,
ScheduledExecutorService sharedExecutor,
long fallbackTimeout,
long recoveryTimeout,
long initializationFallbackTimeout
) {
List<SynchronizerFactoryWithState> synchronizerFactories = synchronizers
.stream()
Expand All @@ -118,7 +150,8 @@ public FDv2DataSource(
this.threadPriority = threadPriority;
this.logger = logger;
this.conditionFactories = new ArrayList<>();
this.conditionFactories.add(new FallbackCondition.Factory(sharedExecutor, fallbackTimeout));
this.conditionFactories.add(new FallbackCondition.Factory(
sharedExecutor, fallbackTimeout, initializationFallbackTimeout, dataApplied::get));
this.conditionFactories.add(new RecoveryCondition.Factory(sharedExecutor, recoveryTimeout));
}

Expand Down Expand Up @@ -210,7 +243,9 @@ private InitializerOutcome runInitializers() {
DataSourceStatusProvider.ErrorInfo fallbackErrorInfo = null;
switch (result.getResultType()) {
case CHANGE_SET:
dataSourceUpdates.apply(result.getChangeSet());
if (dataSourceUpdates.apply(result.getChangeSet())) {
dataApplied.set(true);
}
anyDataReceived = true;
logger.info("Initialized via '{}'.", initializerName);
if (!result.getChangeSet().getSelector().isEmpty()) {
Expand Down Expand Up @@ -405,7 +440,9 @@ private boolean runSynchronizers() {
case CHANGE_SET:
// A data update breaks the "in a row" streak for status deduplication.
resetSynchronizerStatusDedupe();
dataSourceUpdates.apply(result.getChangeSet());
if (dataSourceUpdates.apply(result.getChangeSet())) {
dataApplied.set(true);
}
dataSourceUpdates.updateStatus(DataSourceStatusProvider.State.VALID, null);
// This could have been completed by any data source. But if it has not been completed before
// now, then we complete it.
Expand Down
42 changes: 41 additions & 1 deletion lib/sdk/server/src/main/java/com/launchdarkly/sdk/server/FDv2DataSourceConditions.java
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Expand Up @@ -10,6 +10,7 @@
import java.util.concurrent.ScheduledExecutorService;
import java.util.concurrent.ScheduledFuture;
import java.util.concurrent.TimeUnit;
import java.util.function.BooleanSupplier;

/**
* Container class for FDv2 data source conditions and related types.
Expand Down Expand Up @@ -101,13 +102,35 @@ public Factory(ScheduledExecutorService sharedExecutor, long timeout) {
*/
static class FallbackCondition extends TimedCondition {
static class Factory extends TimedCondition.Factory {
private final long initializationTimeoutSeconds;
private final BooleanSupplier dataApplied;

public Factory(ScheduledExecutorService sharedExecutor, long timeout) {
this(sharedExecutor, timeout, 0, () -> true);
}

/**
* @param initializationTimeoutSeconds how long a synchronizer may go without delivering data, while no
* data has been applied yet, before falling back
* @param dataApplied reports whether the data source has applied any data yet
*/
public Factory(
ScheduledExecutorService sharedExecutor,
long timeout,
long initializationTimeoutSeconds,
BooleanSupplier dataApplied
) {
super(sharedExecutor, timeout);
this.initializationTimeoutSeconds = initializationTimeoutSeconds;
this.dataApplied = dataApplied;
}

@Override
public Condition build() {
return new FallbackCondition(sharedExecutor, timeoutSeconds);
if (dataApplied.getAsBoolean()) {
return new FallbackCondition(sharedExecutor, timeoutSeconds);
}
return new FallbackCondition(sharedExecutor, timeoutSeconds, initializationTimeoutSeconds);
}

@Override
Expand All @@ -120,6 +143,23 @@ public FallbackCondition(ScheduledExecutorService sharedExecutor, long timeoutSe
super(sharedExecutor, timeoutSeconds);
}

/**
* Creates a fallback condition for use before any data has been applied. A synchronizer that never connects
* may not report any status for a long time, so the timer starts immediately instead of waiting for an
* interruption. Receiving a change set cancels it.
*/
public FallbackCondition(
ScheduledExecutorService sharedExecutor,
long timeoutSeconds,
long initializationTimeoutSeconds
) {
super(sharedExecutor, timeoutSeconds);
timerFuture = sharedExecutor.schedule(() -> {
resultFuture.complete(this);
return null;
}, initializationTimeoutSeconds, TimeUnit.SECONDS);
}

@Override
public void inform(FDv2SourceResult sourceResult) {
if (sourceResult.getResultType() == SourceResultType.CHANGE_SET) {
Expand Down
41 changes: 41 additions & 0 deletions ...server/src/test/java/com/launchdarkly/sdk/server/FDv2DataSourceFallbackConditionTest.java
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Expand Up @@ -120,6 +120,47 @@ public void changeSetCancelsActiveTimer() throws Exception {
assertFalse(resultFuture.isDone());
}

@Test
public void initializationTimerCompletesResultFutureWithoutStatus() throws Exception {
executor = Executors.newScheduledThreadPool(1);
FallbackCondition condition = new FallbackCondition(executor, 120, 1);

CompletableFuture<Condition> resultFuture = condition.execute();
assertFalse(resultFuture.isDone());

assertSame(condition, resultFuture.get(2, TimeUnit.SECONDS));
}

@Test
public void changeSetCancelsInitializationTimer() throws Exception {
executor = Executors.newScheduledThreadPool(1);
FallbackCondition condition = new FallbackCondition(executor, 120, 1);

CompletableFuture<Condition> resultFuture = condition.execute();
condition.inform(FDv2SourceResult.changeSet(makeChangeSet(), false));

Thread.sleep(1500);

assertFalse(resultFuture.isDone());
}

@Test
public void factoryOnlyUsesInitializationTimerBeforeDataIsApplied() throws Exception {
executor = Executors.newScheduledThreadPool(1);
java.util.concurrent.atomic.AtomicBoolean dataApplied = new java.util.concurrent.atomic.AtomicBoolean(false);
FallbackCondition.Factory factory = new FallbackCondition.Factory(executor, 120, 1, dataApplied::get);

Condition beforeData = factory.build();
dataApplied.set(true);
Condition afterData = factory.build();

assertSame(beforeData, beforeData.execute().get(2, TimeUnit.SECONDS));
assertFalse(afterData.execute().isDone());

beforeData.close();
afterData.close();
}

@Test
public void changeSetWithoutActiveTimerDoesNothing() throws Exception {
executor = Executors.newScheduledThreadPool(1);
Expand Down
63 changes: 63 additions & 0 deletions lib/sdk/server/src/test/java/com/launchdarkly/sdk/server/FDv2DataSourceTest.java
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Expand Up @@ -1656,6 +1656,69 @@ public void fallbackMovesToNextSynchronizer() throws Exception {
assertNotNull("Second synchronizer should be called after fallback", secondCalled);
}

@Test
public void silentSynchronizerFallsBackBeforeDataIsApplied() throws Exception {
executor = Executors.newScheduledThreadPool(2);
MockDataSourceUpdateSink sink = new MockDataSourceUpdateSink();

ImmutableList<FDv2DataSource.DataSourceFactory<Initializer>> initializers = ImmutableList.of();

// First fails permanently, second never reports anything, third serves data.
BlockingQueue<FDv2SourceResult> firstSyncResults = new LinkedBlockingQueue<>();
firstSyncResults.add(makeTerminalErrorResult());
BlockingQueue<FDv2SourceResult> thirdSyncResults = new LinkedBlockingQueue<>();
thirdSyncResults.add(FDv2SourceResult.changeSet(makeChangeSet(true), false));

BlockingQueue<Boolean> thirdCalledQueue = new LinkedBlockingQueue<>();

ImmutableList<FDv2DataSource.DataSourceFactory<Synchronizer>> synchronizers = ImmutableList.of(
() -> new MockQueuedSynchronizer(firstSyncResults),
() -> new MockQueuedSynchronizer(new LinkedBlockingQueue<>()),
() -> {
thirdCalledQueue.offer(true);
return new MockQueuedSynchronizer(thirdSyncResults);
}
);

// Long steady-state fallback timeout, short initialization fallback timeout.
FDv2DataSource dataSource = new FDv2DataSource(initializers, synchronizers, null, sink, Thread.NORM_PRIORITY, logger, executor, 120, 300, 1);
resourcesToClose.add(dataSource);

Future<Void> startFuture = dataSource.start();
startFuture.get(5, TimeUnit.SECONDS);

assertTrue(dataSource.isInitialized());
assertNotNull("Third synchronizer should be called", thirdCalledQueue.poll(1, TimeUnit.SECONDS));
}

@Test
public void silentSynchronizerDoesNotFallBackQuicklyAfterDataIsApplied() throws Exception {
executor = Executors.newScheduledThreadPool(2);
MockDataSourceUpdateSink sink = new MockDataSourceUpdateSink();

ImmutableList<FDv2DataSource.DataSourceFactory<Initializer>> initializers = ImmutableList.of(
() -> new MockInitializer(CompletableFuture.completedFuture(FDv2SourceResult.changeSet(makeChangeSet(true), false)))
);

BlockingQueue<Boolean> secondCalledQueue = new LinkedBlockingQueue<>();

ImmutableList<FDv2DataSource.DataSourceFactory<Synchronizer>> synchronizers = ImmutableList.of(
() -> new MockQueuedSynchronizer(new LinkedBlockingQueue<>()),
() -> {
secondCalledQueue.offer(true);
return new MockQueuedSynchronizer(new LinkedBlockingQueue<>());
}
);

FDv2DataSource dataSource = new FDv2DataSource(initializers, synchronizers, null, sink, Thread.NORM_PRIORITY, logger, executor, 120, 300, 1);
resourcesToClose.add(dataSource);

Future<Void> startFuture = dataSource.start();
startFuture.get(2, TimeUnit.SECONDS);

assertNull("Second synchronizer should not be called", secondCalledQueue.poll(2, TimeUnit.SECONDS));
}

// ============================================================================
// Condition Lifecycle
// ============================================================================
Expand Down
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