# Multiverso Torch Binding API

## init()

Initialize mutliverso.

This should be called only once before training at the beginning of the whole
project.

## barrier()

Set a barrier for all workers to wait.

Workers will wait until all workers reach a specific barrier.

## shutdown()

Shutdown multiverso.

This should be called only once after finishing training at the end of the whole
project.

## num_workers()

Return the total number of workers.

## worker_id()

Return the id (zero-based index) for current worker.

## TableHandler

`TableHandler` is an interface to sync different kinds of values.

In most cases, you are supposed to sync models (for initialization) and
gradients (during training) so as to let multiverso help you manage the models
in distributed environments. Currently, two types of `TableHandler` are
supported, namely `ArrayTableHandler` and `MatrixTableHandler`.

### ArrayTableHandler

`ArrayTableHandler` is used to sync array-like (one-dimensional) value.

Although our model tends to be a matrix, when using `torch.nn` package we can
get the flattened parameters and gradients with
[module.getParameters()](https://github.com/torch/nn/blob/master/doc/module.md#flatparameters-flatgradparameters-getparameters).
So in most cases, we should use `ArrayTableHandler` instead of
`MatrixTableHandler` we will introduce soon.

#### ArrayTableHandler:new(size)

Create a `ArrayTableHandler` for syncing array-like (one-dimensional) value.

The `size` should be a `number` equal to the size of value we want to sync.

#### ArrayTableHandler:add(data)

Add a array-like (one-dimensional) data to the server.

The `data` should be a `torch.Tensor` or Lua `table`. During training process,
the data should be the gradients (delta value). The size of `data` must be equal
to the size specified in initialization.

#### ArrayTableHandler:get()

Get the array-like (one-dimensional) value from the server.

The value we get will be a `torch.Tensor`. Usually, we are supposed to use
[Tensor:copy()](https://github.com/torch/torch7/blob/master/doc/tensor.md#self-copytensor)
to assign the value to desired destination.

### MatrixTableHandler

`MatrixTableHandler` is used to sync matrix-like (two-dimensional) value.

#### MatrixTableHandler:New(num_row, num_col)

Create a `MatrixTableHandler` for syncing matrix-like (two-dimensional) value.

The `num_row` should be the number of rows and the `num_col` should be the
number of columns. Both of them should be a `number` equal to the exact size of
value we want to sync.

#### MatrixTableHandler:add(data, row_ids)

Add a matrix-like (two-dimensional) data to the server.

Same as the clarification in `ArrayTableHandler`, the `data` should be a
`torch.Tensor` or Lua `table` and we should pass the gradients (delta value) not
the exact value to it. The `row_ids` is an optional parameter and it should be
an array of 'row_id' numbers when specified. If specified, multiverso will only
update the value in specific rows and the size of `data` should be equal to the
size of value we want to update.

#### MatrixTableHandler:get(row_ids)

Get the matrix-like (two-dimensional) value from the server.

The `row_ids` is an optional parameter and the interface works the same way as
`ArrayTableHandler` when `row_ids` is not specified. But when we pass an array
of `row_id` numbers, we will only get the value form specific rows. In this way,
we can not do a `Tensor:copy()` but have to deal with the value manually.