* Reduce contention on the global module rwlock
This commit intendes to close#4025 by reducing contention on the global
rwlock Wasmtime has for module information during instantiation and
dropping a store. Currently registration of a module into this global
map happens during instantiation, but this can be a hot path as
embeddings may want to, in parallel, instantiate modules.
Instead this switches to a strategy of inserting into the global module
map when a `Module` is created and then removing it from the map when
the `Module` is dropped. Registration in a `Store` now preserves the
entire `Module` within the store as opposed to trying to only save it
piecemeal. In reality the only piece that wasn't saved within a store
was the `TypeTables` which was pretty inconsequential for core wasm
modules anyway.
This means that instantiation should now clone a singluar `Arc` into a
`Store` per `Module` (previously it cloned two) with zero managemnt on
the global rwlock as that happened at `Module` creation time.
Additionally dropping a `Store` again involves zero rwlock management
and only a single `Arc` drop per-instantiated module (previously it was
two).
In the process of doing this I also went ahead and removed the
`Module::new_with_name` API. This has been difficult to support
historically with various variations on the internals of `ModuleInner`
because it involves mutating a `Module` after it's been created. My hope
is that this API is pretty rarely used and/or isn't super important, so
it's ok to remove.
Finally this change removes some internal `Arc` layerings that are no
longer necessary, attempting to use either `T` or `&T` where possible
without dealing with the overhead of an `Arc`.
Closes#4025
* Move back to a `BTreeMap` in `ModuleRegistry`
Alex Crichton
90791a0e32