Hi Vince, On Sun, Nov 8, 2009 at 7:58 PM, Vince Bonfanti <[email protected]> wrote:
> > Hi Nick, > > Thanks for your feedback. Yes, I'm very interested in seeing this > included in the official SDK. What are the steps from here? > See this doc: http://groups.google.com/group/google-appengine/web/how-to-submit-a-patch-to-the-sdk > > See responses to specific questions inserted below. > > Vince > > > - Perhaps make PermanentTaskFailure a runtime exception, which would > > eliminate the need to declare it on methods that throw it. > > That's fine. I generally prefer checked exceptions, but if the > AppEngine team prefers unchecked exceptions, I'm happy to make this > change. > I wouldn't say we prefer them in general - but personally, I think common uses of PermanentTaskFailure fit into the same sort of category as out of memory errors, divisions by zero, and so forth - they're not predictable at design-time. > > - If you do the above, you could make the Deferrable interface extend > > Runnable, as suggested in the meeting. I'm not sure that's appropriate, > > since the implications of Runnable are different. > > I think Runnable is not appropriate. I also looked at Callable, but in > the end thought a new interface--Deferrable--was the best option. > Fair enough. > > > - I'm not sure there's any need to be able to pass arguments to the > > Deferrable, since users will already have to declare a deferrable class > and > > instantiate it. I'm open to convincing, though. > > I put the arguments there to mimic the Python API and then realized > later they're not really needed. Removing the arguments also > simplifies the code by eliminating the need for the TaskHolder > class--the Deferrable class could be serialized directly. I'm happy to > remove the arguments if that's what the AppEngine team decides is > best. > Since the Java version is inevitably different due to the need for a custom class instead of a function object, I'd vote to drop the arguments. > > > - Have you tested tasks of size exactly MaxTaskSizeBytes? At least in > > Python, the actual limit seems to include some overhead that varies from > > task to task. > > No, I haven't tested this yet. > > > - If payload isn't an instance of TaskHolder, the task will silently > return > > - it should log an error. > > I think the only way payload won't be an instance of TaskHolder is if > the deserialize() method returns null, in which case an error has > already been logged. But I'll double-check this. > The other possibility is that something else serialized an object and sent it to your task handler - or possibly, that a future version of your own code did so. I think logging an error (but returning a 200 status code) would be the best policy, so these sorts of situations are debuggable. -Nick Johnson > > Are you interested in having this included in the official SDK? > > -Nick > > On Sat, Oct 31, 2009 at 7:08 PM, Vince Bonfanti <[email protected]> > wrote: > >> > >> This looked like an interesting problem, and I already had most of the > >> pieces in place, so here's my first attempt, which is implemented in a > >> single class (also attached, along with some test files): > >> > >> > >> > http://code.google.com/p/gaevfs/source/browse/trunk/src/com/newatlanta/appengine/taskqueue/Deferred.java > >> > >> I'm more than happy to contribute this for inclusion in the SDK. > >> > >> Some caveats: > >> > >> 1) Because of issue #2097 > >> (http://code.google.com/p/googleappengine/issues/detail?id=2097), this > >> doesn't work on the development server (it does work in production). > >> So go star that issue! > >> > >> 2) I've only done minimal testing on the production server (see the > >> attached test files). > >> > >> 3) This post is the only documentation that's currently available. > >> > >> First, add the following your your web.xml: > >> > >> <servlet> > >> <servlet-name>Deferred</servlet-name> > >> > >> > <servlet-class>com.newatlanta.appengine.taskqueue.Deferred</servlet-class> > >> </servlet> > >> <servlet-mapping> > >> <servlet-name>Deferred</servlet-name> > >> <url-pattern>/_ah/queue/deferred</url-pattern> > >> </servlet-mapping> > >> > >> Second, define the "deferred" queue within queue.xml (use whatever > >> rate you want): > >> > >> <queue> > >> <name>deferred</name> > >> <rate>10/s</rate> > >> </queue> > >> > >> Next, create a class that implements the > >> com.newatlanta.appengine.taskqueue.Deferred.Deferrable interface; the > >> "doTask()" method of this class is where you implement your task > >> logic. > >> > >> Then, invoke the com.newatlanta.appengine.taskqueue.Deferred.defer() > >> method to queue up your task: > >> > >> TestDeferred testDeferred = new TestDeferred(); // implements > >> Deferrable > >> Deferred.defer( testDeferred, "one", "two", "three", 1, 2, 3 ); > >> > >> (Note that it would be possible to pass arguments as attributes to > >> your Deferrable instance, rather than using varargs; I'm not sure it > >> makes much difference which you choose). > >> > >> Just as for the Python implementation, if the arguments size exceeds > >> 10KB, the arguments are stored in a datastore entity, which is then > >> deleted when the task is executed. Also, your doTask() method can > >> throw a PermanentTaskFailure exception to halt retries; any other > >> exceptions cause the task to be retried. > >> > >> Let me know if you find this useful, have any questions or encounter > >> any problems. > >> > >> Vince > >> > >> On Fri, Oct 30, 2009 at 6:13 PM, Jason (Google) <[email protected]> > >> wrote: > >> > Hi David. This may be coming to Java eventually, but it hasn't been > >> > started > >> > yet. If you or anyone else is interested in contributing, let me know. > >> > > >> > - Jason > >> > > >> > On Wed, Oct 28, 2009 at 7:52 AM, David Chandler < > [email protected]> > >> > wrote: > >> >> > >> >> Re: http://code.google.com/appengine/articles/deferred.html > >> >> > >> >> Will this be coming to AppEngine for Java? > >> >> > >> >> David Chandler > >> >> http://turbomanage.wordpress.com > >> >> > >> >> > >> > > >> > > >> > > > >> > > >> > >> > > > > > > > > -- > > Nick Johnson, Developer Programs Engineer, App Engine > > Google Ireland Ltd. :: Registered in Dublin, Ireland, Registration > Number: > > 368047 > > > > > > > > > > > -- Nick Johnson, Developer Programs Engineer, App Engine Google Ireland Ltd. :: Registered in Dublin, Ireland, Registration Number: 368047 --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "Google App Engine for Java" group. 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