Tasks and Concurrency

FScript supports concurrent thunk execution through the default Task module surface.

Task.spawn and Task.await are provided by the default runtime extern registry, so an embedding host may choose not to expose them.

Task type

Task values use the native postfix type form:

'a task

Examples:

int task
string list task

Tasks are opaque handles. You create them with Task.spawn and observe them with Task.await.

Spawning work

Task.spawn schedules a thunk for concurrent execution and returns immediately.

let work =
  Task.spawn (fun () -> 21 * 2)

Signature:

Task.spawn : (unit -> 'a) -> 'a task

FScript writes unit -> 'a in the type, and fun () -> ... is the preferred way to express that thunk.

Awaiting results

Use Task.await to wait for completion and extract the result value.

let work = Task.spawn (fun () -> 21 * 2)
let answer = Task.await work
Console.writeLine $"{answer}"

Signature:

Task.await : 'a task -> 'a

Concurrency model

• Spawned thunks run concurrently on the host runtime thread pool.
• Side effects may interleave across tasks and with the main script.
• Task.await is the explicit synchronization point for a task result.

Failure model

FScript errors are fatal. Tasks follow the same rule.

• If a spawned thunk fails, the task has failed.
• Task.await on that task fails the script with the same fatal runtime error.
• Finishing a program with unawaited tasks is also a runtime error.

There is no catch/recovery mechanism in FScript today.

Example

let a = Task.spawn (fun () -> 40 + 2)
let b = Task.spawn (fun () -> 10 * 3)

let result = (Task.await a, Task.await b)
Console.writeLine $"{result}"

For a larger example, see samples/parallel-quicksort.fss.