qi.Future API ¶
Promise and Future are a way to synchronise data between multiples threads. The number of future associated to a promise is not limited. Promise is the setter, future is the getter. Basically, you have a task to do, that will return a value, you give it a Promise. Then you have others thread that depend on the result of that task, you give them future associated to that promise, the future will block until the value or an error is set by the promise.
Constants that describe the state of the Future. This is the status returned by
qi.FutureState.None The future is not bound. qi.FutureState.Running The future is attached to a Promise. qi.FutureState.Canceled The future has been canceled qi.FutureState.FinishedWithError The future has finished and an error is available qi.FutureState.FinishedWithValue The future has finished and a value is available
import qi import time import functools def doSomeWork(p): #do your work here instead of sleeping time.sleep(1) p.setValue(42) p = qi.Promise() f = p.future() qi.async(functools.partial(doSomeWork, p)) print "result:", f.value()
import qi import time import functools def doSomeWork(p): #do your work here instead of sleeping time.sleep(1) p.setValue(42) def resultReady(f): if f.hasValue(): print "Value:", f.value() elif f.hasError(): print "Error:", f.error() p = qi.Promise() f = p.future() qi.async(functools.partial(doSomeWork, p)) #resultReady will be called even if the result is already there. f.addCallback(resultReady)
Cancellation support ¶
In some situations, you will want to create asynchronous operations that can be
interrupted in the middle of their execution. For that you can set a callback
to the promise that will be called when someone asks for cancellation or just
on the promise.
import qi import time from functools import partial class FakeOperation: def doStep(self): time.sleep(0.3) print 'I executed one step' def longOperation(self, promise): "do steps or cancel before the end" for i in range(10): if promise.isCancelRequested(): print 'Cancel requested, aborting' promise.setCanceled() return self.doStep() # if an error occurred, promise.setError("error") # use setValue if everything went ok print 'longOperation finished' promise.setValue(None) def asyncLongOperation(self): "start long operation and return a future" promise = qi.Promise() qi.async(partial(self.longOperation, promise)) return promise.future() m = FakeOperation() fut = m.asyncLongOperation() time.sleep(1) fut.cancel() assert fut.wait() == qi.FutureState.Canceled assert fut.isCanceled() assert fut.isFinished()