Error on async job - grails

Question

I'm trying to create an async task that will not block the request. The user make the request, the task will start, and the controller will render "Job is running...", this is for avoid the request being blocked waiting the task to complete.
Once the task is finish, it will execute the onComplete and do something with the result of that task (for example call a service that will send a mail to an user)
| Error 2014-09-16 17:38:56,721 [Actor Thread 3] ERROR gpars.LoggingPoolFactory - Async execution error: null
The code is the following:
package testasync
import static grails.async.Promises.*
class TestController {
def index() {
//Create the job
def job1 = task {
println 'Waiting 10 seconds'
Thread.sleep(10000)
return 'Im done'
}
//On error
job1.onError { Throwable err ->
println "An error occured ${err.message}"
}
//On success
job1.onComplete { result ->
println "Promise returned $result"
}
render 'Job is running...'
}
Complete stacktrace:
| Error 2014-09-17 10:35:24,522 [Actor Thread 3] ERROR gpars.LoggingPoolFactory - Async execution error: null
Message: null
Line | Method
->> 72 | doCall in org.grails.async.factory.gpars.GparsPromise$_onError_closure2
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
| 62 | run in groovyx.gpars.dataflow.DataCallback$1
| 1145 | runWorker in java.util.concurrent.ThreadPoolExecutor
| 615 | run in java.util.concurrent.ThreadPoolExecutor$Worker
^ 745 | run . . . in java.lang.Thread

Answer 1

I ended using the executor framework with the grails-executor plugin. I uploaded a very basic example here: https://github.com/agusl88/grails-async-job-queuqe
That code is using a "custom" version of the grails-executor plugin, i merged some PR's from the plugin repo and packaged as jar just for testing propuses. The repo of the plugin is this: https://github.com/basejump/grails-executor

Answer 2

I was able to get rid of this exception in a controller by removing the onComplete and onError calls. I guess the exception happens because the parent thread ended when you called render.
So your:
Promise p = task {
complexAsyncMethodCall(); // (1) do stuff
}
.onComplete { result -> println result } // (2) on success
.onError { Throwable t -> System.err.println("Error: " + t) } // (3) on error
Becomes:
Promise p = task {
try {
def result = complexAsyncMethodCall(); // (1) do stuff
println result // (2) on success
} catch(Throwable t) {
System.err.println("Error: " + t) // (3) on error
}
}
This adds coupling between your work (1) and the result processing (2 and 3) but you could overcome this by writing your own Closure wrapper that takes extra Closures as arguments. Something like this:
// may not work! written off the top of my head
class ProcessableClosure<V> extends Closure<V> {
Closure<V> work;
Closure<?> onError;
Closure<?> onComplete;
#Override
public V call(Object... args) {
try {
def result = work.call(args); // (1) do stuff
onComplete.call(result); // (2) on complete
} catch(Exception e) {
onError.call(result); // (3) on error
}
}
}
That makes your code more readable:
Closure doWork = { complexAsyncMethodCall(); } // (1) do stuff
Closure printResult = { println it } // (2) on complete
Closure logError = { Throwable t -> log.error t } // (3) on error
Closure runEverythingNicely = new ProcessableClosure(work: doWork, onComplete: printResult, onError: logError)
Promise p = task { runEverythingNicely }

Answer 3

When creating a Promise async task inside a controller you actually have to return the response by calling the get() method on the task, or the onError and onComplete methods will never be called. Adding:
job1.get()
Before your call to render will resolve the issue.

Answer 4

In my case, just returning a promise worked.
MyService.groovy
import static grails.async.Promises.*
def getAsync(){
Promise p = task {
//Long running task
println 'John doe started digging a hole here.'
Thread.sleep(2000)
println 'John doe working......'
return 'Kudos John Doe!'
}
p.onError { Throwable err ->
println "Poor John"+err
}
p.onComplete { result ->
println "Congrats." +result
}
println 'John Doe is doing something here.'
return p
}