Groovy - 等待承诺列表

Question

I have several promises in my program and I need to wait on all of them simulateneously before moving on. For Grails , I found the following example:

def p1 = task { 2 * 2 }
def p2 = task { 4 * 4 }
def p3 = task { 8 * 8 }
assert [4,16,64] == waitAll(p1, p2, p3)

I know Grails is heavily relying on GPars , but I cannot find the reference to waitAll anywhere in there. Grails also supports PromiseList , which I cannot find in Groovy or GPars either. Can anyone point me in the right direction?

Answer 1

waitAll is a Grails specific static method from Promises class. It internally built on GPars whenAllBound method which you can use for your implementation.

Answer 2

Thanks to defectus and Feras Odeh , I could figure out the correct way of doing it with whenAllBound . Just to save everyone else a bit of time, here is a working code example:

import static groovyx.gpars.dataflow.Dataflow.task
import static groovyx.gpars.dataflow.Dataflow.whenAllBound;

def p1 = task { 2 * 2 }
def p2 = task { 4 * 4 }
def p3 = task { 8 * 8 }
def total = whenAllBound(p1, p2, p3, { List<?> values -> values })
assertTrue([4,16,64] == total.get())

whenAllBound expects a closure that is called with the results of all promises. I simply collect them and return them as they are. Also, whenAllBound returns a promise itself, so you will need to call the .get() method on it (see assertion statement).

Answer 3

The truth it's in the source code.

import groovyx.gpars.dataflow.Dataflow

def <T> List<groovyx.gpars.dataflow.Promise<T>> toGparsPromises(List<Promise<T>> promises) {
    final List<groovyx.gpars.dataflow.Promise<T>> dataflowPromises = promises.collect() { it -> (groovyx.gpars.dataflow.Promise<T>)((GparsPromise<T>)it).internalPromise }
    dataflowPromises
}

private static Closure<List<?>> originalValuesClosure = { List<?> values -> values }

def <T> List<T> waitAll(List<Promise<T>> promises) {
    final groovyx.gpars.dataflow.Promise<List<T>> promise = (groovyx.gpars.dataflow.Promise<List<T>>)Dataflow.whenAllBound(toGparsPromises(promises), originalValuesClosure)
    return promise.get()
}

https://github.com/grails/grails-core/blob/master/grails-async/src/main/groovy/org/grails/async/factory/gpars/GparsPromiseFactory.groovy