Uno/Spec/Cascaded Mapping
Type: Specification State: final Claim: recommended
Feature
Cascaded mapping generalizes the runtimes search&connect algorithm in a way, that it always finds a mapping between any two particular (purpose) environments, necessarily falling back to the generic Uno environment for mediation, in case no specialized bridges (mappings) can be found.
For example:
uno::Mapping("gcc3:unsafe", "gcc3")
gets mediated via the "unsafe_uno_uno" purpose bridge: => Mapping("gcc3:unsafe" -> "uno:unsafe" -> "uno" -> "gcc3")
Mapping Algorithm
- In case both environments are of the same purpose, map directly, e.g.
"uno:unsafe" -> "gcc3:unsafe" => "uno:unsafe" -gcc3_uno-> "gcc3:unsafe" . - Mediate through a purpose bridge, in case it is asked for a mapping between different purposes, e.g.
"uno:unsafe" -unsafe_uno_uno-> "uno", the purpose bridge here is "unsafe_uno_uno". - Mediate through the "uno" environment, if asked for a mapping from one purpose environment to another purpose environment, e.g.
"uno:unsafe" -> "uno:affine" => "uno:unsafe" -unsafe_uno_uno-> "uno" -affine_uno_uno-> "uno:affine". - Recursively apply -4- in case a multi purpose environment has been specified, e.g.
"gcc3:unsafe:debug" -> "gcc3:affine" => "gcc3:unsafe:debug" -gcc3_uno-> "uno:unsafe:debug" -debug_uno_uno-> "uno:unsafe" -unsafe_uno_uno-> "uno" -affine_uno_uno-> "uno:affine" -gcc3_uno-> "gcc3:affine". - Always map through the nearest "uno:<purpose>" environment, e.g.
"gcc3:debug:unsafe" <-> "gcc3:debug:affine" => "gcc3:debug:unsafe" -gcc3_uno-> "uno:debug:unsafe" -unsafe_uno_uno-> "uno:debug" -affine_uno_uno-> "uno:debug:affine" -gcc3_uno-> "gcc3:debug:unsafe". - Shortcut if possible, no is mediation necessary, should directly map through purpose, e.g.
"uno:debug:affine" -> "uno:debug" => "uno:debug:affine" -affine_uno_uno-> "uno:debug".
The mapping algorithm does not know any particular purpose. It is just leverages the current purpose API.
Rationale
The introduction of purpose environments allows to instantiate multiple environments of the same ABI (e.g. "gcc3") but with different purposes. Cascaded mappings allows to map between environments of different purposes, by using the Uno runtimes purpose mapping mechanism.
