Java API to get the size of output list operations

[kbsriram]

This opens up access to the TF_OperationOutputListLength C API from java, for operations that return output lists.

[tensorflow-jenkins]

Can one of the admins verify this patch?

[asimshankar]

Thanks very much for the PR! Much appreciated.
A couple of minor things, otherwise looks great.

[asimshankar]

I'd suggest elaborating a bit here since the notion of a "name" might not be obvious. How about something like:

/**
 * Returns the size of the list of Tensors produced by this operation.
 *
 * <p/>An Operation has multiple named outputs, each of which produces either
 * a single tensor or a list of tensors. This method returns the size of
 * the list of tensors for a specific output of the operation.
 *
 * @param name identifier of the list of tensors (of which there may be many) produced by this operation.
 * @returns the size of the list of Tensors produced by this operation.
 * @throws ...

[asimshankar]

It might be better to have a helper function return the integer value and then the assert call can be in the test, that way the line number rendered on test failures is more useful and you don't need to use the string names to locate the failure. Something like:

public void outputListLength() {
  assertEquals(1, split(new int[]{0, 1}, 1));
  assertEquals(2, split(new int[]{0, 1}, 2));
  assertEquals(3, split(new int[]{0,1,2}, 3));
}

@Test
public void  outputListLengthFailsOnInvalidName() {
  ...
}

private int split(int[] values, int num_split) {
  try (Graph g = new Graph()) {
    return g.opBuilder("Split", "Split")
      .addInput(TestUtil.constant(g, "split_dim", 0))
      .addInput(TestUtil.constant(g, "values", values)
      .setAttr("num_split", num_split)
      .build()
      .outputListLength("output");
  }
}

[kbsriram]

great suggestions @asimshankar - thanks, and I've incorporated them wholesale.

[asimshankar]

Thanks for the PR!

[vrv]

@tensorflow-jenkins test this please