Tokei says that we've got ~76k lines of Rust.
I used ripgrep to find occurrences of `Arc::` (to exclude type signatures and only find constructors) and then just gave it a quick manual look to exclude tests and benchmarks.
This leaves me with:
- one data structure that contains general application state and contextual information, which is created at application startup and shared across all tasks/threads
- one data structure for accumulating results that is shared across threads. This is an Arc<Mutex<u64, SomeEnum>>. The less common of the two enum variants is an Arc<BTreeMap>.
- one data structure used to pass a database connection in to a context where it'll be used to spawn async tasks
All told, we've only got four places in production paths where we construct a new Arc. One of those four is only called once in the life cycle of the application, while the others are called for any given invocation.
FWIW I write Rust professionally now, and in our entire codebase we have maybe four or five data structures containing Arcs, specifically where objects are spawned as Futures on other threads.