Running futures at user background priority

Long running futures executed at the same priority as futures used by the user interface can slow down the entire user interface.

AsyncFutureExecutionUserBackgroundPriority AsyncFutureExecutionPriority subclass: #AsyncFutureExecutionUserBackgroundPriority instanceVariableNames: '' classVariableNames: '' package: 'Futures-Executor' is a priority for futures that is lower than the lowest priority used by the user interface.

The simplest way to execute a computation in a worker process at this priority is using BlockClosure>>#asAsyncPromiseWithUserBackgroundPriority asAsyncPromiseWithUserBackgroundPriority ^ self asAsyncFuture awaitWithUserBackgroundPriority .

promise := [ 50000 factorial ] asAsyncPromiseWithUserBackgroundPriority
  

promise := [ 50000 factorial ] asAsyncFuture
	awaitWithUserBackgroundPriority
  

If more control is needed over these computations thet can be run also in dedicated workers.

promise := [ 50000 factorial ] asAsyncFuture
	awaitWithUserBackgroundPriorityInCustomGroup: #MyWorker
  

promise := [ 50000 factorial ] asAsyncFuture
	await: (AsyncFutureExecutionConfiguration new 
		userBackgroundPriority;
		customGroup: #MyWorker)
  

In case multiple such computations are needed and they might also need to wait for the results of other computations, one further option is to use BlockClosure>>#asAsyncForkedFuture asAsyncForkedFuture ^ AsyncForkPollFuture pollBlock: self to create futures that run in their own process instead of the worker process.

promise := [ 50000 factorial ] asAsyncForkedFuture
	awaitWithUserBackgroundPriority
  

In the code snippet below the worker is responsible for managing the execution of the future in a dedicated process. While the future runs, the worker is free to execute other futures.

promise := [ 50000 factorial ] asAsyncForkedFuture
	await: (AsyncFutureExecutionConfiguration new 
		userBackgroundPriority;
		customGroup: #MyWorker)