viewflow.io:实现队列任务

Question

我想用ViewFlow library实现以下用例

问题

由用户启动的特定流的进程在执行芹菜作业之前必须在队列中等待。每个用户都有一个这些进程的队列。根据调度或手动触发，允许队列中的下一个进程继续进行。

示例

我的流中的节点进入命名队列。对于每个队列，应用程序中的其他逻辑确定何时允许下一个任务继续。选择队列中的下一个任务，并调用其激活的done()方法。

示例流程可能如下所示：

class MyFlow(Flow):

    start = flow.Start(...).Next(queue_wait)
    queue_wait = QueueWait("myQueue").Next(job)
    job = celery.Job(...).Next(end)
    end = flow.End()

问题

实现排队的最佳方法是什么？在上面的例子中，我不知道"QueueWait“应该是什么。

我已经通读了文档和视图流代码，但我还不清楚这是否可以使用内置的Node和Activation类(如func.Function )来完成，或者是否需要使用自定义类进行扩展。

Answer 1

经过多次实验，我得出了一个可行且简单的解决方案：

from viewflow.flow import base
from viewflow.flow.func import FuncActivation
from viewflow.activation import STATUS


class Queue(base.NextNodeMixin,
            base.UndoViewMixin,
            base.CancelViewMixin,
            base.DetailsViewMixin,
            base.Event):

    """
    Node that halts the flow and waits in a queue. To process the next waiting task
    call the dequeue method, optionally specifying the task owner.

    Example placing a job in a queue::

        class MyFlow(Flow):
            wait = Queue().Next(this.job)
            job = celery.Job(send_stuff).Next(this.end)
            end = flow.End()

        somewhere in the application code:
        MyFlow.wait.dequeue()
        or:
        MyFlow.wait.dequeue(process__myprocess__owner=user)

    Queues are logically separated by the task_type, so new queues defined in a
    subclass by overriding task_type attribute.
    """

    task_type = 'QUEUE'
    activation_cls = FuncActivation

    def __init__(self, **kwargs):
        super(Queue, self).__init__(**kwargs)

    def dequeue(self, **kwargs):
        """
        Process the next task in the queue by created date/time. kwargs is
        used to add task filter arguments, thereby effectively splitting the queue
        into subqueues. This could be used to implement per-user queues.

        Returns True if task was found and dequeued, False otherwise
        """
        filter_kwargs = {'flow_task_type': self.task_type, 'status': STATUS.NEW}
        if kwargs is not None:
            filter_kwargs.update(kwargs)

        task = self.flow_cls.task_cls.objects.filter(**filter_kwargs).order_by('created').first()
        if task is not None:
            lock = self.flow_cls.lock_impl(self.flow_cls.instance)
            with lock(self.flow_cls, task.process_id):
                task = self.flow_cls.task_cls._default_manager.get(pk=task.pk)
                activation = self.activation_cls()
                activation.initialize(self, task)
                activation.prepare()
                activation.done()
            return True

        return False

我试图使其尽可能通用，并支持多个命名队列和子队列的定义，例如每个用户的队列。