Note: None of this is implemented.
The detailed design for Cone's concurrence capability is unfinished. Most of the heavy lifting for concurrence is handled by library packages, rather than language capabilities. For now, this page offers a sketch of the sort of concurrrency capabilities to expect to see at some point.
Libraries provide the ability to spawn additional OS-based processes or threads. A spawned thread is an owned resource, where move semantics make support for structured concurrency possible. The finalizer for the thread effectively joins that thread with the current one.
The reference permissions prevent race conditions between threads that share access to the same memory. They can do this, as the compiler knows what data types are able to move references from one thread to another. Among these library-defined types are lockless deques that can be used as communicating channels between threads.
Using OS threads, one can build a pool of work-stealing worker threads that accept channel-enqueud work requests from anywhere. The nature of the work request could be any message, including a closure, co-routine or actor. The type-compatible work scheduler pops its work off the queue and dispatches it, in many cases expecting it to run quickly to completion.
There will likely be some metaprogramming and method-call syntax sugar to make it easy to make message passing look like a method call.
Generally speaking, work requests that make use of blocking i/o should be performed on an extra native thread so as to not degrade the throughput and latency of non-blocking work. It is possible that functions will be annotated (like purity) such that the compiler can detect whether a thread is known to not block.
Co-routines and Asynchronous I/O
In some cases, dispatched work may be a co-routine that yields before finishing. The dispatcher needs to know how to handle the data types yielded from these co-routines, how to reschedule the work, and how to pass expected data back in on resumption.
A common use of such yielding co-routines is when a work thread wants to issue non-blocking i/o requests. Any i/o functions it uses automatically yield after submitting the i/o request, suspending work on the co-routine. After the i/o thread determines the i/o request has been handled, it triggers the co-routine to be rescheduled and resumed, feeding it the appropriate Result from that request.