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Async Execution

This scene demonstrates how to use async execution. Async execution allows a some running code to be paused and then resumed later. This is similar to a Unity coroutine but it can work with any program, even ones which were not designed for async execution! For more information about using async execution, see this tutorial.

The Demo Object has a AsyncDemoScript attached which is loading the "AsyncWat" asset. This asset has the Asyncify option ticked in the importer, which rewrites the WASM code to add support for async suspend/resume. Once the AsyncDemoScript is loaded it begins running in a Unity coroutine.

The running WASM code looks like this:

;; get a number (the current time)
(call $.get_number)

;; suspend execution until the "Complete" button is clicked
(drop (call $wasi_snapshot_preview1.sched_yield))

;; get another number  (the current time)
(call $.get_number)

;; Return both numbers

The running WASM code is suspended and will remain suspended until the "Complete" button is clicked. While suspended no CPU resources are used at all. Once the button is clicked it will finish running and displays the difference between the two numbers.

  1. Inspect AsyncWat
    • Asyncify has been ticked in the "Transformation" section
  2. Open AsyncDemoScript
    • DemoCoroutine calls the "run()" method and receives a Future object.
    • Once created a Future must be run to completion, it cannot be cancelled!
    • yield return future; will resume the future once every frame until it is complete.
    • future.TryGetResult will attempt get a result from the future if it is complete.
    • When future.TryGetResult returns true it has returned a valid result and has internally disposed the future, it must not be called again.