fix: address threading and resource management feedback on android-sdk-framework

android-sdk-framework/src/main/java/cloud/eppo/android/framework/BaseAndroidClient.java

@@ -38,8 +38,8 @@ public class BaseAndroidClient<JsonFlagType> extends BaseEppoClient<JsonFlagType
   private static final long DEFAULT_POLLING_INTERVAL_MS = 5 * 60 * 1000;
   private static final long DEFAULT_JITTER_INTERVAL_RATIO = 10;
 
-  private long pollingIntervalMs;
-  private long pollingJitterMs;
+  private volatile long pollingIntervalMs;
+  private volatile long pollingJitterMs;
 
   /**
    * Protected constructor. Use Builder to construct instances.

android-sdk-framework/src/main/java/cloud/eppo/android/framework/storage/CachingConfigurationStore.java

@@ -43,6 +43,10 @@ protected CachingConfigurationStore(
   /**
    * Saves the configuration to storage and updates the in-memory cache.
    *
+   * <p>The disk write is performed first. The in-memory cache is updated only after the write
+   * succeeds, ensuring that the in-memory state never reflects a configuration that failed to
+   * persist. Concurrent saves are safe: the last write to complete successfully wins in memory.
+   *
    * @param config the configuration to save (must not be null)
    * @return a future that completes when the write finishes, or completes exceptionally if the
    *     underlying {@link ByteStore} write fails (e.g. with an {@link java.io.IOException})
@@ -53,26 +57,16 @@ protected CachingConfigurationStore(
     if (config == null) {
       throw new IllegalArgumentException("config must not be null");
     }
-    Configuration previousConfiguration = configuration.get();
     byte[] bytes = codec.toBytes(config);
-    configuration.set(config); // optimistic update — in-memory reflects last submitted save
     return byteStore
         .write(bytes)
         .whenComplete(
             (v, ex) -> {
-              if (ex != null) {
-                // Revert the optimistic update, but only if no later save has superseded this
-                // one. compareAndSet atomically checks that the in-memory value is still the
-                // one we wrote; if a concurrent save has already advanced it, the revert is
-                // skipped.
-                //
-                // Edge case: if two concurrent saves both fail their IO writes, the second
-                // failure's revert may land on a value that was itself never persisted (the
-                // first save's value). This is acceptable — the in-memory state may diverge
-                // from disk, but the next successful save will reconcile them. Saves are
-                // serialized through a single-thread IO_EXECUTOR, so true concurrent IO
-                // failures are unlikely in practice.
-                configuration.compareAndSet(config, previousConfiguration);
+              if (ex == null) {
+                // Only update in-memory cache after a successful disk write.
+                // Use set() rather than compareAndSet() so the most-recently-persisted
+                // configuration always wins, regardless of submission order.
+                configuration.set(config);
               }
             });
   }

android-sdk-framework/src/main/java/cloud/eppo/android/framework/storage/FileBackedByteStore.java

@@ -1,19 +1,24 @@
 package cloud.eppo.android.framework.storage;
 
 import java.util.concurrent.CompletableFuture;
-import java.util.concurrent.Executor;
+import java.util.concurrent.ExecutorService;
 import java.util.concurrent.Executors;
 import org.jetbrains.annotations.NotNull;
 
 /**
  * {@link ByteStore} implementation that reads and writes a single file via {@link BaseCacheFile}.
+ *
+ * <p>Implements {@link java.io.Closeable}. Call {@link #close()} when the store is no longer needed
+ * to release the background IO thread. If not closed explicitly, the daemon thread will be
+ * reclaimed by the JVM/Android runtime on process exit.
  */
-public final class FileBackedByteStore implements ByteStore {
+public final class FileBackedByteStore implements ByteStore, java.io.Closeable {
 
   // Dedicated single-thread executor avoids saturating ForkJoinPool.commonPool() with blocking I/O
-  // on low-core-count Android devices. Daemon thread so the executor does not block JVM/process
-  // exit in test environments (e.g. Robolectric).
-  private static final Executor IO_EXECUTOR =
+  // on low-core-count Android devices. Instance-level (not static) so it can be shut down via
+  // close(). The thread is a daemon so it does not block JVM/process exit when close() is omitted
+  // (e.g. in test environments such as Robolectric).
+  private final ExecutorService ioExecutor =
       Executors.newSingleThreadExecutor(
           r -> {
             Thread t = new Thread(r, "eppo-io");
@@ -30,6 +35,15 @@ public FileBackedByteStore(@NotNull BaseCacheFile cacheFile) {
     this.cacheFile = cacheFile;
   }
 
+  /**
+   * Shuts down the background IO executor. In-flight operations are allowed to complete; no new
+   * operations will be accepted after this call.
+   */
+  @Override
+  public void close() {
+    ioExecutor.shutdown();
+  }
+
   @Override
   @NotNull public CompletableFuture<byte[]> read() {
     return CompletableFuture.supplyAsync(
@@ -43,7 +57,7 @@ public FileBackedByteStore(@NotNull BaseCacheFile cacheFile) {
             throw new RuntimeException("Failed to read from cache file", e);
           }
         },
-        IO_EXECUTOR);
+        ioExecutor);
   }
 
   @Override
@@ -59,7 +73,7 @@ public FileBackedByteStore(@NotNull BaseCacheFile cacheFile) {
             throw new RuntimeException("Failed to write to cache file", e);
           }
         },
-        IO_EXECUTOR);
+        ioExecutor);
   }
 
   private static byte[] readAllBytes(java.io.InputStream in) throws java.io.IOException {

eppo/src/main/java/cloud/eppo/android/EppoClient.java

@@ -34,7 +34,7 @@ public class EppoClient extends BaseEppoClient {
 
   private long pollingIntervalMs, pollingJitterMs;
 
-  @Nullable private static EppoClient instance;
+  @Nullable private static volatile EppoClient instance;
 
   private EppoClient(
       String apiKey,