GAG - A Directed-Acyclic-Graph JIT in Go

GAG is a library I created while developing https://isobot.io to experiment with different ways of implementing the core runtime.

It intends to be a fast, highly parallel, DAG JIT, while still maintaining the balance between performance and usability.

While the runtime is included in this library, a significantly more complex type system would need to be implemented ontop of GAG before it would likely be useful for any such similar use case.

Concepts

Similar to traditional DAGs, there are 4 fundamental primatives in GAG:

• Graph
  • A collection of Nodes & Edges
• Vertex
  • A field on a node
• Edge
  • A connection between two vertex
• Node
  • A unit of work with inputs and outputs, analagous to a function

Execution

Unlike traditional Flow-Based Programming, GAG includes the concept of "executing" or "running" a node. This fundamentally controls the flow of the graph's execution. Nodes can include an Execution type in their Output field which will be linked to the next node at runtime.

Caching

GAG also caches the Output fields of any node that has already been run. In the future when the JIT is improved this may only conditionally occur when it is optimal.

Examples

A rather trival graph that simply adds 2 numbers together to compare the sum and panic depending on the result could be represented as such:

&Graph{
	Nodes: []Node{
		{Name: "Adder"},
		{Name: "Comparer"},
		{Name: "Panicer"},
	},
	Edges: []Edge{
		{Output: Vertex{Raw: 1}, Input: Vertex{ID: 0, Field: "Number1"}},
		{Output: Vertex{Raw: 2}, Input: Vertex{ID: 0, Field: "Number2"}},
		{Output: Vertex{ID: 0, Field: "Sum"}, Input: Vertex{ID: 1, Field: "Number1"}},
		{Output: Vertex{Raw: 4}, Input: Vertex{ID: 1, Field: "Number2"}},
		{Output: Vertex{ID: 1, Field: "Greater"}, Input: Vertex{ID: 2}},
	},
}

Where the implementation of the Adder and Comparer nodes look like:

type Adder struct {
	Input struct {
		Number1 int
		Number2 int
	}

	Output struct {
		Sum int
	}
}

func (a *Adder) Run(ctx *Context) error {
	a.Output.Sum = a.Input.Number1 + a.Input.Number2
	return nil
}

type Comparer struct {
	Input struct {
		Number1 int
		Number2 int
	}

	Output struct {
		Greater Execution
		Less    Execution
	}
}

func (c *Comparer) Run(ctx *Context) error {
	if c.Input.Number1 > c.Input.Number2 {
		return c.Output.Greater(ctx)
	}

	return c.Output.Less(ctx)
}

The graph can also be visually represented like:

Or in isobot.io:

TODO

• Allow tainting specific outputs to invalidate downstream caches
• Additional node lifecycle methods

WARNINGS

There is lots of unsafe non-standard reflection going on in this project. It is not nearly tested enough to be used in production, and there are likely many dragons hiding in the code itself.