cavis/contrib/codegen-tools/codegen/adr/0007-configuration_objects.md

Configuration Objects

Status

ACCEPTED

Discussed by Alex Black, raver119 and Paul Dubs on 27. November 2019.

Context

Some Ops (esp. convolution) have many parameters. Many of them can have reasonable defaults, but even then creating signatures for evey reasonable configuration may be impossible, as those signatures would require different naming in order to be actually distinguishable from each other.

In other cases, an op may have a lot of same typed parameters that are required (e.g. GRU, LSTM, SRU) but it is very easy to mix them up.

For both of those cases (many optional parameters, easily mixed up required parameters) it is reasonable to use a config holder with builder pattern in languages that do not support named or default parameters.

In our current codebase those configurations are often used across several related ops.

Decision

We add a Config("name"){ ... } section to the namespace context. It supports Input and Arg definitions in the same way that Op does.

Ops that want to use that config can use useConfig(conf). As configs are often reused across related objects, this will have the effect of a mixin: All inputs and args defined in that config will also be automatically defined on that Op. If there is a naming conflict, an exception will be thrown at construction time.

For default signatures, configs will be passed at the end, in the order that they were added to the Op.

If other signatures are desired, configs, like regular inputs and args, can be passed to Signature.

In languages that do not support default or named parameters, a config holder will be created, that will take the parameters of the config using a builder pattern. For languages with default and named parameters, no additional config holder will be created, and the parameters of the config will be treated as if they were directly configured on the Op.

Example

This example shows a very simple case in order to highlight how this feature would be used.

fun RNN() = Namespace("RNN"){
    val sruWeights = Config("SRUWeights"){
        Input(FLOATING_POINT, "weights"){ description = "Weights, with shape [inSize, 3*inSize]" }
        Input(FLOATING_POINT, "bias"){ description = "Biases, with shape [2*inSize]" }
    }

    Op("SRU"){
        Input(FLOATING_POINT, "x"){ description = "..." }
        Input(FLOATING_POINT, "initialC"){ description = "..." }
        Input(FLOATING_POINT, "mask"){ description = "..." }
        
        useConfig(sruWeights)
    
        Output(FLOATING_POINT, "out"){ description = "..." }
    }
    
    Op("SRUCell"){
        val x = Input(FLOATING_POINT, "x"){ description = "..." }
        val cLast = Input(FLOATING_POINT, "cLast"){ description = "..." }
        
        val conf = useConfig(sruWeights)
    
        Output(FLOATING_POINT, "out"){ description = "..." }
    
        // Just for demonstration purposes
        Signature(x, cLast, conf)
    }
}

Consequences

Advantages

• Ops that share parameters can make that sharing explicit
• Easier definition of related ops with common parameters
• Simplifies usage of complex ops in languages without named parameters

Disadvantages

• Not all parameters are defined directly within an op anymore
• Configs are not shareable across namespaces