This demo looks at using higher-order RPC programming model provided by Cap’n Proto for implementing distributed promises.
We have been exploring how Pulumi can benefit from distributed promise broker capabilities. That is, we want promises to be constructed, cross-referenced and resolved across as set of subprocesses in different languages.
Implementing this over gRPC would involve a <promise-id: str> being
passsed through the RPC layer, since gRPC is first-order. In contrast,
here we have more of an illusion of a single-process programming
model:
interface PromiseBroker {
newPromise @0 () -> (promise :Promise);
}
interface PromiseCallback {
done @0 (data: Data) -> ();
}
interface Promise {
then @0 (callback :PromiseCallback) -> ();
resolve @1 (data: Data) -> ();
}
It is an interesting programming model and the current implementation is just a quick demo and is not ready to be relied on. Some questions remain around lifetimes of the Promise and PromiseCallback proxy objects and interoperability of N clients.
$ nix-shell --pure
$ make
In one shell:
$ ./pulumi-go-capnp/pulumi-capnp-demo server
Starting server on port :8000...
Allocating PromiseBroker
...
In another shell:
$ ./pulumi-capnp-demo client
Waiting on the promise to be resolved
CB2: Received: OK then..
CB1: Received: OK then..