run something async in Grails 2.3

Question

In My Grails service, there is a part of a method I wish to run asynchronously.

Following, the doc for 2.3.x http://grails.org/doc/2.3.0.M1/guide/async.html

I do

public class MyService {
    public void myMethod() {
        Promise p = task {
            // Long running task
        }
        p.onError { Throwable err ->
            println "An error occured ${err.message}"
        }
        p.onComplete { result ->
            println "Promise returned $result"
        }
        // block until result is called
        def result = p.get()
    }
}

However, I want to execute mine without any blocking. The p.get() method blocks. How do I execute the promise without any sort of blocking. I don't care if myMethod() returns, it is a kinda of fire and forget method.

Answer 1

So, according to the documentation if you don't call .get() or .waitAll() but rather just make use of onComplete you can run your task without blocking the current thread.

Here is a very silly example that I worked up in the console to as a proof of concept.

import static grails.async.Promises.*
def p = task {
    // Long running task
    println 'Off to do something now ...'
    Thread.sleep(5000)
    println '... that took 5 seconds'
    return 'the result'
}

p.onError { Throwable err ->
    println "An error occured ${err.message}"
}
p.onComplete { result ->
    println "Promise returned $result"
}

println 'Just to show some output, and prove the task is running in the background.'

Running the above example gives you the following output:

Off to do something now ...  
Just to show some output, and prove the task is running in the background.  
... that took 5 seconds   
Promise returned the result