fix: Log the isFlagKnown cached-data warning only once per client

Author: kinyoklion

lib/sdk/server/src/main/java/com/launchdarkly/sdk/server/LDClient.java

@@ -40,6 +40,7 @@
 import java.util.concurrent.ThreadFactory;
 import java.util.concurrent.TimeUnit;
 import java.util.concurrent.TimeoutException;
+import java.util.concurrent.atomic.AtomicBoolean;
 
 import static com.google.common.base.Preconditions.checkNotNull;
 import static com.launchdarkly.sdk.server.DataModel.FEATURES;
@@ -66,6 +67,8 @@ public final class LDClient implements LDClientInterface {
   private final ScheduledExecutorService sharedExecutor;
   private final LDLogger baseLogger;
   private final LDLogger evaluationLogger;
+  // isFlagKnown logs its cached-data warning once per client. This flag records that log.
+  private final AtomicBoolean isFlagKnownCachedDataWarned = new AtomicBoolean(false);
 
   private static final int EXCESSIVE_INIT_WAIT_MILLIS = 60000;
 
@@ -429,7 +432,10 @@ public boolean isFlagKnown(String featureKey) {
 
     if (!isInitialized()) {
       if (store.isInitialized()) {
-        baseLogger.warn("isFlagKnown called before client initialized for feature flag \"{}\"; using last known values from data store", featureKey);
+        if (isFlagKnownCachedDataWarned.compareAndSet(false, true)) {
+          baseLogger.warn("isFlagKnown called before client initialized for feature flag \"{}\"; "
+              + "using last known values from data store. This message is logged once.", featureKey);
+        }
       } else {
         baseLogger.warn("isFlagKnown called before client initialized for feature flag \"{}\"; data store unavailable, returning false", featureKey);
         return false;

lib/sdk/server/src/test/java/com/launchdarkly/sdk/server/LDClientTest.java

@@ -1,5 +1,6 @@
 package com.launchdarkly.sdk.server;
 
+import com.launchdarkly.logging.LDLogLevel;
 import com.launchdarkly.sdk.LDContext;
 import com.launchdarkly.sdk.LDValue;
 import com.launchdarkly.sdk.server.integrations.MockPersistentDataStore;
@@ -427,6 +428,30 @@ public void isFlagKnownReturnsFalseIfStoreAndClientAreNotInitialized() throws Ex
     mocks.verifyAll();
   }
 
+  @Test
+  public void isFlagKnownLogsCachedDataWarningOnlyOnce() throws Exception {
+    DataStore testDataStore = initedDataStore();
+    LDConfig.Builder config = new LDConfig.Builder()
+            .startWait(Duration.ZERO)
+            .dataStore(specificComponent(testDataStore));
+    expect(dataSource.start()).andReturn(initFuture);
+    expect(dataSource.isInitialized()).andReturn(false).times(2);
+    mocks.replayAll();
+
+    client = createMockClient(config);
+
+    upsertFlag(testDataStore, flagWithValue("key", LDValue.of(1)));
+    assertTrue(client.isFlagKnown("key"));
+    assertTrue(client.isFlagKnown("key"));
+
+    long warningCount = logCapture.getMessages().stream()
+        .filter(m -> m.getLevel() == LDLogLevel.WARN
+            && m.getText().contains("using last known values from data store"))
+        .count();
+    assertEquals(1, warningCount);
+    mocks.verifyAll();
+  }
+
   @Test
   public void isFlagKnownUsesStoreIfStoreIsInitializedButClientIsNot() throws Exception {
     DataStore testDataStore = initedDataStore();