Create a Queue
When you create a Queue, several Worker processes are created in the background. You can then evaluate R code on those background processes while your main R process is free to do other work.
Important
The background processes are persisent R sessions. Avoid modifying their
.GlobalEnv, otherwise your R code will produce different results based on which Worker evaluates it.
Create a Job
Main article: vignette('eval')
job <- q$run({ paste('Hello', 'World!') })This Job will begin evaluating immediately, assuming no other Jobs are ahead of it in the Queue.
Access the Result
Main article: vignette('results')
job$result
#> [1] "Hello World!"Running <Job>$result will block until the Job
finishes and the result is ready.
Add a Callback Hook
Main article: vignette('hooks')
job$on('done', function (job) message(job$result))
#> [1] "Hello World!"Adding a callback hook to trigger when the Job is done allows the result to be handled without blocking the main R process.
Interrupt Evaluation
Main article: vignette('stops')
job <- q$run({ Sys.sleep(10); 'Zzzzz' })
job$stop()
job$result
#> <interrupt: job stopped by user>If the Job’s result is no longer needed and you want to free up
compute resources, calling <Job>$stop() will
terminate the background process. Terminated background process are
automatically replaced by new ones.
Passing Data
# Variables to permanently store on the Worker.
q <- Queue$new(globals = list(MY_DATA = mtcars))
# Variables to temporary add to the Worker.
vars <- list(n = 2, fields = c('mpg', 'cyl', 'disp'))
# The expression to evaluate on the Worker.
expr <- quote(head(MY_DATA, n)[,fields])
job <- q$run(expr = expr, vars = vars)
job$result
#> mpg cyl disp
#> Mazda RX4 21 6 160
#> Mazda RX4 Wag 21 6 160