Grails中的异步编程

| Error 2014-04-29 11:10:24,125 [Actor Thread 28] ERROR gpars.LoggingPoolFactory  - Async execution error: null
Message: null
    Line | Method
->>   61 | doCall    in org.grails.async.factory.gpars.GparsPromise$_onComplete_closure1
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 
|     62 | run       in groovyx.gpars.dataflow.DataCallback$1
|   1145 | runWorker in java.util.concurrent.ThreadPoolExecutor
|    615 | run       in java.util.concurrent.ThreadPoolExecutor$Worker
^    724 | run . . . in java.lang.Thread

请帮我解决这个问题.

这是守则

//Promise 1
    Promise p1 = task {
        println id+" p1 Task is Runing"
        sleep(4000) 
        println id+" p1 Thread Woke Up"
        return "p1Completed"
    }

    //Promise 2
    Promise p2 = task {
        println id+" p2 Task is Runing"    
        sleep(4000)
        println id+" p2 Thread Woke Up"
        return "p2Completed"
    }
    p1.onComplete { result ->
        println id+" Promise p1 Completed returned "+result  
    }
    p1.onError { Throwable err ->
        println id+" p1 An error occured ${err.message}"
    }
    p2.onComplete { result ->
        println id+" Promise p2 Completed returned "+result
    }
    p2.onError { Throwable err ->
        println id+" p2 An error occured ${err.message}"
    }