* might be cancelled before we set the runner thread. That would make it impossible to
     * interrupt, yet it will still run, since interruptTask will leave the runner value null,
     * allowing the CAS below to succeed.
     */
    Thread currentThread = Thread.currentThread();
    if (!compareAndSet(null, currentThread)) {
      return; // someone else has run or is running.
    }

      Java8Compatibility.flip(buf);
      to.append(buf);
      total += buf.remaining();
      Java8Compatibility.clear(buf);
    }
    return total;
  }

  // TODO(lukes): consider allowing callers to pass in a buffer to use, some callers would be able
  // to reuse buffers, others would be able to size them more appropriately than the constant
  // defaults

  /**

        message.append(", ").append(t.getMessage());
      }
      return message.toString();
    }
  }

  /**
   * Internal Lock implementations implement the {@code CycleDetectingLock} interface, allowing the
   * detection logic to treat all locks in the same manner.
   */
  private interface CycleDetectingLock {

    /** @return the {@link LockGraphNode} associated with this lock. */

       * if the task completed with an error.
       */
      V get() throws CancellationException, ExecutionException, InterruptedException {

        // Acquire the shared lock allowing interruption.
        acquireSharedInterruptibly(-1);
        return getValue();
      }

      /**
       * Implementation of the actual value retrieval. Will return the value on success, an

       * if the task completed with an error.
       */
      V get() throws CancellationException, ExecutionException, InterruptedException {

        // Acquire the shared lock allowing interruption.
        acquireSharedInterruptibly(-1);
        return getValue();
      }

      /**
       * Implementation of the actual value retrieval. Will return the value on success, an

      return b == null ? null : checkNotNull(doBackward(b));
    } else {
      return unsafeDoBackward(b);
    }
  }

  /*
   * LegacyConverter violates the contract of Converter by allowing its doForward and doBackward
   * methods to accept null. We could avoid having unchecked casts in Converter.java itself if we
   * could perform a cast to LegacyConverter, but we can't because it's an internal-only class.
   *

 * read-write locks. Conceptually, lock striping is the technique of dividing a lock into many
 * <i>stripes</i>, increasing the granularity of a single lock and allowing independent operations
 * to lock different stripes and proceed concurrently, instead of creating contention for a single
 * lock.
 *

      return b == null ? null : checkNotNull(doBackward(b));
    } else {
      return unsafeDoBackward(b);
    }
  }

  /*
   * LegacyConverter violates the contract of Converter by allowing its doForward and doBackward
   * methods to accept null. We could avoid having unchecked casts in Converter.java itself if we
   * could perform a cast to LegacyConverter, but we can't because it's an internal-only class.
   *

    try {
      separated.withSeparator("$", 4);
      fail("Expected UnsupportedOperationException");
    } catch (UnsupportedOperationException expected) {
    }
  }

  public void testBase64() {
    // The following test vectors are specified in RFC 4648 itself
    testEncodingWithSeparators(base64(), "", "");
    testEncodingWithSeparators(base64(), "f", "Zg==");
    testEncodingWithSeparators(base64(), "fo", "Zm8=");

    return Optional.of(1);
  }

  private static FluentIterable<? extends Number> getSomeNumbers() {
    return FluentIterable.from(ImmutableList.<Number>of());
  }

  /*
   * The following tests demonstrate the shortcomings of or() and test that the casting workaround
   * mentioned in the method Javadoc does in fact compile.
   */

  @SuppressWarnings("unused") // compilation test