@GwtCompatible(emulated = true)
@ElementTypesAreNonnullByDefault
/*
 * I have decided not to bother adding @ParametricNullness annotations in this class. Adding them is
 * a lot of busy work, and the annotation matters only when the APIs to be annotated are visible to
 * Kotlin code. In this class, nothing is publicly visible (nor exposed indirectly through a
 * publicly visible subclass), and I doubt any of our current or future Kotlin extensions for the

      } catch (Exception // sneaky checked exception
          | Error atomicReferenceFieldUpdaterFailure) {
        // Some Android 5.0.x Samsung devices have bugs in JDK reflection APIs that cause
        // getDeclaredField to throw a NoSuchFieldException when the field is definitely there.
        // For these users fallback to a suboptimal implementation, based on synchronized. This will

   * illustrated <a
   * href="http://unicode.org/cldr/utility/list-unicodeset.jsp?a=%5Cp%7Bwhitespace%7D">here</a>.
   * This is not the same definition used by other Java APIs. (See a <a
   * href="https://goo.gl/Y6SLWx">comparison of several definitions of "whitespace"</a>.)
   *
   * <p>All Unicode White_Space characters are on the BMP and thus supported by this API.
   *

   * illustrated <a
   * href="http://unicode.org/cldr/utility/list-unicodeset.jsp?a=%5Cp%7Bwhitespace%7D">here</a>.
   * This is not the same definition used by other Java APIs. (See a <a
   * href="https://goo.gl/Y6SLWx">comparison of several definitions of "whitespace"</a>.)
   *
   * <p>All Unicode White_Space characters are on the BMP and thus supported by this API.
   *

   * the {@code Future} is already done. Second, if buggy code calls {@code getDone} on a {@code
   * Future} that is still pending, the program will throw instead of block. This can be important
   * for APIs like {@link #whenAllComplete whenAllComplete(...)}{@code .}{@link
   * FutureCombiner#call(Callable, Executor) call(...)}, where it is easy to use a new input from