如何识别GAE提取队列中是否已经存在任务？

Question

Before adding a task to the pull queue, I have to confirm whether same task exists already within queue, if exists should skip task adding to queue. Adding task with name doesn't work for me as it doesn't expire until seven days from the queue even deleted.

We can list tasks using REST API . In the same way, can we get the list of tasks within GAE module or is there any other way to find whether task exists in the queue within Google App Engine module?

Thanks

Answer 1

If task names does not work with logic of your app you can create a corresponding db entity (empty, just a key) that would serve as a flag that the tasks is in the queue. You should put it to db in transaction with a task and delete when task completed.

It would cost you 1 read & 4 write (2 for insert & 2 for delete) operations per each task - nothing comes free.

As alternative you can consider to have some counter in your business entity that would be a part of task name.

Let's say you have entity User and a property TaskCounter.

Then you would add task as:

tasks.add(taskName="TASKNAME" + str(user.id) + str(user.TaskCounter)) - that would insure you can have just 1 active task per entity. Of course you would need to update the property when the task finishes. If you update the entity in the task anyway it costs you almost nothing.