public void testOr_supplier_present() {
    assertThat(Optional.of("a").or(Suppliers.ofInstance("fallback"))).isEqualTo("a");
  }

  public void testOr_supplier_absent() {
    assertEquals("fallback", Optional.absent().or(Suppliers.ofInstance("fallback")));
  }

  public void testOr_nullSupplier_absent() {

        }

        // Runtime exceptions and other errors are likely not recoverable
        return false;
    }

    /**
     * Check if error suggests fallback to TCP is needed
     *
     * @param error the error to check
     * @return true if TCP fallback is recommended
     */
    public boolean shouldFallbackToTcp(Exception error) {
        // Hardware errors suggest RDMA is not working

import jcifs.internal.smb2.rdma.RdmaCapability;
import jcifs.internal.smb2.rdma.RdmaConnection;
import jcifs.internal.smb2.rdma.RdmaMemoryRegion;
import jcifs.internal.smb2.rdma.RdmaProvider;

/**
 * TCP fallback RDMA provider.
 *
 * This provider uses regular TCP connections but maintains the RDMA
 * interface for compatibility. It only supports send/receive operations
 * and does not provide true RDMA read/write capabilities.
 */

   * java.util.concurrent.CompletableFuture#thenAcceptAsync}.
   *
   * @param callback The callback to invoke when this {@code Future} is completed.
   * @param executor The executor to run {@code callback} when the future completes.
   */
  public final void addCallback(FutureCallback<? super V> callback, Executor executor) {
    Futures.addCallback(this, callback, executor);
  }

        // Test fallback logic
        assertTrue(errorHandler.shouldFallbackToTcp(hardwareError), "Hardware errors should suggest TCP fallback");
        assertFalse(errorHandler.shouldFallbackToTcp(timeoutError), "Timeout errors should not immediately suggest TCP fallback");

        // Test error classification using public API

      Class<Throwable> exceptionType,
      Function<? super Throwable, ? extends V> fallback,
      Executor executor) {
    return (FluentFuture<V>) Futures.catching(this, exceptionType, fallback, executor);
  }

  public final FluentFuture<V> catchingAsync(
      Class<Throwable> exceptionType,
      AsyncFunction<? super Throwable, ? extends V> fallback,
      Executor executor) {

        // TCP fallback doesn't support real RDMA read
        throw new UnsupportedOperationException("RDMA read not supported by TCP fallback");
    }

    @Override
    public void rdmaWrite(RdmaMemoryRegion localRegion, long remoteAddress, int remoteKey, int length) throws IOException {
        // TCP fallback doesn't support real RDMA write

      Function<? super Throwable, ? extends V> fallback,
      Executor executor) {
    return AbstractCatchingFuture.create(input, exceptionType, fallback, executor);
  }

  public static <V extends @Nullable Object> ListenableFuture<V> catchingAsync(
      ListenableFuture<? extends V> input,
      Class<Throwable> exceptionType,
      AsyncFunction<? super Throwable, ? extends V> fallback,
      Executor executor) {

### [Fast Fallback](https://square.github.io/okhttp/5.x/okhttp/okhttp3/-ok-http-client/-builder/fast-fallback)

Since version 5.0, `OkHttpClient` supports fast fallback, which is our implementation of Happy Eyeballs [RFC 6555](https://datatracker.ietf.org/doc/html/rfc6555).

     * Execute a callable through the circuit breaker with fallback
     *
     * @param <T> return type
     * @param callable the callable to execute
     * @param fallback fallback supplier if circuit is open
     * @return the result or fallback value
     * @throws Exception if execution fails and no fallback provided
     */
    public <T> T call(Callable<T> callable, Callable<T> fallback) throws Exception {