The lucet compiler and runtime each assume the other is implemented correctly, and its the job of some external system to make sure the runtime only loads code that came from the compiler. (We have infrastructure at Fastly that already does this for our edge cloud, and every use case will have different requirements).

The shared object code, when executed with lucet-runtime, should provide guarantees equivalent to those given by the wasm spec. However, we're not 100% to spec compliance yet, so there are some corners (e.g. import globals) that are not implemented. These dont cause a problem in practice, at the moment, because none of the toolchains we use to emit wasm use those features.

Loading code into the runtime is fast because its mostly a call to `dlopen`, followed by deserializing some metadata (with effort made to make this as efficient as possible). Instantiating modules is fast because it amortizes the syscall overhead by having pools of instances mostly-set-up ahead of time.

I'm guessing Lucet was developed concurrently with the others, but unlike them, it had an extended period of internal development and testing first.

We started the codebase that became Lucet in July 2017. It went through a few fast iterations, and by Jan 2018 we had Cranelift running with AOT compilation. In the early days of Cranelift that meant adding support for position-independent code output and filling in a bunch of gaps in the x86_64 encodings and other really low level stuff. At the time, wasmtime (under the name wasm-standalone, i think?) was a lot less mature, and wasmer was not public yet. So, in a sense, we did (& continue to) contribute to both of those runtimes via Cranelift and other dependencies like Faerie.

We spent the bulk of 2018 solving performance and integration problems, rather than cleaning up the codebase to the point where we could open source it. In the meantime wasmer was released, and both wasmtime and wasmer made a ton of progress. Now that our stuff is open source, it is easier for us to collaborate with other runtimes, possibly by moving more code back into the common Cranelift parent, or by adopting modules from each other.

At the moment, a lot of WASM tooling assumes instances interact with a JS engine. So, we aren't compatible with a bunch of existing tooling, like Rust's wasm-bindgen. We're working on our own tool to fill that hole in the ecosystem.

We also aren't 100% of the way to spec compliance yet. We have a plan to get there, but spent the last year or so putting the bulk of our effort into performance and integration with our edge cloud systems.

We hope so! Mozilla has been working on WASI support from Rust, and our team is working on supporting it from AssemblyScript as well: https://github.com/jedisct1/wasa.