### **4.1 Spark Pi**

Test the Spark installation by running the following compute intensive example, which calculates pi by “throwing darts” at a circle. The program generates points in the unit square ((0,0) to (1,1)) and counts how many points fall within the unit circle within the square. The result approximates pi.

          continue
        }

        if (readBytesDelivered != -1L) {
          return readBytesDelivered
        }

        if (errorExceptionToDeliver != null) {
          // We defer throwing the exception until now so that we can refill the connection
          // flow-control window. This is necessary because we don't transmit window updates until

      s.addValue("removalListener");
    }
    return s.toString();
  }

  /**
   * Returns the number of nanoseconds of the given duration without throwing or overflowing.
   *
   * <p>Instead of throwing {@link ArithmeticException}, this method silently saturates to either
   * {@link Long#MAX_VALUE} or {@link Long#MIN_VALUE}. This behavior can be useful when decomposing

      s.addValue("removalListener");
    }
    return s.toString();
  }

  /**
   * Returns the number of nanoseconds of the given duration without throwing or overflowing.
   *
   * <p>Instead of throwing {@link ArithmeticException}, this method silently saturates to either
   * {@link Long#MAX_VALUE} or {@link Long#MIN_VALUE}. This behavior can be useful when decomposing

       *   user task -- which means that we already got past this code (or else we exited early
       *   above))
       */
      // Unconditionally set; there is no risk of throwing away a queued task from another thread,
      // because in order for the current task to run on this executor the previous task must have

   * AssertionFailedError thrown, so that the current testcase will fail.
   */
  public void threadAssertFalse(boolean b) {
    try {
      assertFalse(b);
    } catch (AssertionFailedError t) {
      threadRecordFailure(t);
      throw t;
    }
  }

  /**
   * Just like assertNull(x), but additionally recording (using threadRecordFailure) any

    accumulator.add(ONE_VALUE);
    for (int power = 1; power < Long.SIZE - 1; power++) {
      accumulator.addAll(accumulator.snapshot());
    }
    // Should overflow without throwing.
    accumulator.addAll(accumulator.snapshot());
    assertThat(accumulator.count()).isLessThan(0L);
  }

  public void testMean() {
    assertThrows(IllegalStateException.class, () -> emptyAccumulator.mean());

       *   user task -- which means that we already got past this code (or else we exited early
       *   above))
       */
      // Unconditionally set; there is no risk of throwing away a queued task from another thread,
      // because in order for the current task to run on this executor the previous task must have

   * However, this method doesn't throw an exception in that situation, but instead keeps the
   * original {@code fromKey}. Similarly, this method keeps the original {@code toKey}, instead of
   * throwing an exception, if passed a {@code toKey} greater than an earlier {@code toKey}.
   */
  @Override
  public ImmutableSortedMap<K, V> subMap(K fromKey, K toKey) {
    return subMap(fromKey, true, toKey, false);
  }

  /**
   * Pre-defined {@link Policy} implementations.
   *
   * @since 13.0
   */
  public enum Policies implements Policy {
    /**
     * When potential deadlock is detected, this policy results in the throwing of the {@code
     * PotentialDeadlockException} indicating the potential deadlock, which includes stack traces
     * illustrating the cycle in lock acquisition order.
     */
    THROW {
      @Override