Vince, shouldn't you use an un-named Task queue (to avoid Naming rules mentioned) but query your own datastore semaphore prior to adding to the queue. This way when task N runs it manages the semaphore (a Entity) to implement a mutex begin/end sequence. I believe this implies that task N will in fact run 3 transactions: #1 - mutex begin (create Entity), #2 - work for N, and #3 - mutex end (remove Entity).
Anyhow assuming your logic to trigger a new Task N can incorporate the criteria for mutex exists, then what would keep this from working? On Dec 1, 2:37 pm, Vince Bonfanti <[email protected]> wrote: > BTW, I've noticed that the dev server actually behaves the way I would like > it to. It only throws a "Task name already exists" exception while the task > is queued; as soon as the task runs it allows you to queue up another task > with the same name. > > I guess I'll just open a feature request on this in the issue tracker. > > Vince > > > > On Tue, Dec 1, 2009 at 11:39 AM, Vince Bonfanti <[email protected]> wrote: > > I'm trying to solve the following problem using task queues: > > > 1. Queue a task to perform some action "N". > > 2. Until action N has been performed, don't allow any other tasks to be > > queued that also perform action N. > > 3. As soon as action N has been performed, immediately allow other tasks > > to be queued to perform action N (repeat from step 1). > > > Using task names almost accomplishes what I need, except that at step 3 it > > will be at least seven days before another task can be queued to perform > > action N, when I need it to be allowed immediately: > > > "This (task names) provides a lightweight mechanism for ensuring > > once-only semantics. Once a Task with name N is written, any subsequent > > attempts to insert a Task named N will fail. Eventually (at least seven days > > after the task successfully executes), the task will be deleted and the name > > N can be reused." > > > I've thought of different ways to solve this, most likely by using a > > memcache flag as a semaphore. But, it would be nice if the task queue API > > could support this natively, maybe by adding a "reuse time" or "exclusion > > time" parameter when setting the TaskOptions name parameter. > > > Any thoughts on this? > > > Vince- Hide quoted text - > > - Show quoted text - -- You received this message because you are subscribed to the Google Groups "Google App Engine for Java" group. To post to this group, send email to [email protected]. To unsubscribe from this group, send email to [email protected]. For more options, visit this group at http://groups.google.com/group/google-appengine-java?hl=en.
