Tasks and Concurrency

FScript supports concurrent thunk execution through the built-in Task module.

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.