Graphex
=======

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A library for composing and executing task graphs in elixir.

### Add as Dependency

```elixir
{:graphex, "~> 0.1.1"}
```

Also, be sure to add `:graphex` to your application's list of OTP applications since it has a supervision tree that must be started before using the library.

## Usage

Each node is represented by a separate process so tasks will run in parallel if possible. Failed nodes will be retried automatically per the default supervision restart settings.

```elixir
incr = fn node ->
  fn r -> r[node] + 1
end

result = exec_graph :e, [
  [name: :a, fun: fn _ -> 0 end],
  [name: :b, fun: incr.(:a), deps: [:a]],
  [name: :c, fun: incr.(:b), deps: [:b]],
  [name: :d, fun: incr.(:b), deps: [:b]],
  [name: :e, fun: incr.(:c), deps: [:c]],
]

assert result == 3
```

## Errors and Retries

Each node can be automatically retried if the function causes the process to die. In order to automatically retry, just set the `:tries` attribute to a number greater than 1.

```elixir
  [name: :b, fun: something_that_might_error(), deps: [:some_data], tries: 3],
```

This would automatically retry vertex `:b` up to 3 times.

If the node fails all tries, it will publish `{:error, {:graphex, some_error}}` to all of the nodes that depend on it.