*
 * @param <K> the most general key type this builder will be able to create caches for. This is
 *     normally {@code Object} unless it is constrained by using a method like {@link
 *     #removalListener}. Cache keys may not be null.
 * @param <V> the most general value type this builder will be able to create caches for. This is
 *     normally {@code Object} unless it is constrained by using a method like {@link

        toClose.add(it)
      }
    assertFailsWith<IOException> {
      cache["k1"]
    }

    // Now let it operate normally.
    filesystem.setFaultyDelete(cacheDir / "k1.0.tmp", false)
    filesystem.setFaultyDelete(cacheDir, false)
    val snapshot = cache["k1"]
    assertThat(snapshot).isNull()
  }

  @Test

 *
 * @param <K> the most general key type this builder will be able to create caches for. This is
 *     normally {@code Object} unless it is constrained by using a method like {@link
 *     #removalListener}. Cache keys may not be null.
 * @param <V> the most general value type this builder will be able to create caches for. This is
 *     normally {@code Object} unless it is constrained by using a method like {@link

            dependency.

            The term "scope" comes from the OAuth2 specification, it seems to be
            intentionally vague and interpretable. It normally refers to permissions,
            in cases to roles.

            These scopes are integrated with OpenAPI (and the API docs at `/docs`).
            So they are visible in the OpenAPI specification.
            )

   *     cancelled regardless
   * @return {@code false} if the step could not be cancelled, typically because it has already
   *     completed normally; {@code true} otherwise
   */
  @CanIgnoreReturnValue
  @SuppressWarnings("Interruption") // We are propagating an interrupt from a caller.
  public boolean cancel(boolean mayInterruptIfRunning) {

      if (value == null) {
        tryDrainReferenceQueues();
        return null;
      }

      return value;
    }

    /**
     * Performs routine cleanup following a read. Normally cleanup happens during writes, or from
     * the cleanupExecutor. If cleanup is not observed after a sufficient number of reads, try
     * cleaning up from the read thread.
     */
    void postReadCleanup() {