从Tornado调用Celery任务

Question

怎么从tornado里调用一个celery任务，并通过回调获取结果呢？

这篇文章说，只需要通过RabbitMQ发送一条消息，任务就会被执行。这听起来没问题，但有没有人能给个python的例子（最好是用tornado，并带上回调）？我个人是用mongodb作为消息中介，但我也可以换成Redis或者RabbitMQ。

补充一下，我想要一个带回调的例子。比如，这段tornado代码

TestTask.delay(callback = self._on_celery_response) 
...
def _on_celery_response(self, result):
    print "hello from _on_celery_repsonse" , result

是不能工作的。我的TestTask是：

class TestTask(Task):
    name = "tornadoServer.Test"
    def run(self, callback=None,  **kwargs):
        result = {'result': "hello from celery task invoked by tornado"}
        if callback is not None:
            subtask(callback).delay(result)
        return result

还有错误追踪信息：

    File "/home/hymloth/Desktop/DJANGO/NOO1/tornadoServer/tornado/stack_context.py", line 183, in wrapped
    callback(*args, **kwargs)
  File "/home/hymloth/Desktop/DJANGO/NOO1/tornadoServer/asyncmongo/connection.py", line 183, in _parse_response
    callback(response)
  File "/home/hymloth/Desktop/DJANGO/NOO1/tornadoServer/asyncmongo/cursor.py", line 399, in _handle_response
    orig_callback(result['data'], error=None)
  File "/home/hymloth/Desktop/DJANGO/NOO1/tornadoServer/basic_auth_handlers.py", line 66, in _on_response
    celery_tasks.TestTask.delay(self._on_celery_response)
  File "/usr/local/lib/python2.6/dist-packages/celery-2.2.7-py2.6.egg/celery/task/base.py", line 338, in delay
    return self.apply_async(args, kwargs)
  File "/usr/local/lib/python2.6/dist-packages/celery-2.2.7-py2.6.egg/celery/task/base.py", line 460, in apply_async
    **options)
  File "/usr/local/lib/python2.6/dist-packages/celery-2.2.7-py2.6.egg/celery/app/amqp.py", line 230, in delay_task
    send(body, exchange=exchange, **extract_msg_options(kwargs))
  File "/usr/local/lib/python2.6/dist-packages/kombu-1.1.6-py2.6.egg/kombu/compat.py", line 101, in send
    return self.publish(*args, **kwargs)
  File "/usr/local/lib/python2.6/dist-packages/kombu-1.1.6-py2.6.egg/kombu/messaging.py", line 124, in publish
    compression, headers)
  File "/usr/local/lib/python2.6/dist-packages/kombu-1.1.6-py2.6.egg/kombu/messaging.py", line 147, in _prepare
    body) = encode(body, serializer=serializer)
  File "/usr/local/lib/python2.6/dist-packages/kombu-1.1.6-py2.6.egg/kombu/serialization.py", line 119, in encode
    payload = encoder(data)
  File "/usr/lib/python2.6/copy_reg.py", line 70, in _reduce_ex
    raise TypeError, "can't pickle %s objects" % base.__name__
TypeError: can't pickle instancemethod objects

这个任务在没有回调的情况下是可以正常工作的……有什么建议吗？

Answer 1

Celery 有一个回调函数，你可以去这个链接了解更多信息：http://ask.github.com/celery/userguide/tasksets.html

from celery.task import task
from celery.task.sets import subtask

@task
def add(x, y, callback=None):
    result = x + y

    if callback is not None:
        subtask(callback).delay(result)

    return result

Answer 2

回调对象也应该是一个celery任务，否则你的代码就无法正常工作。

如果你的回调函数不需要是celery任务，你可以在任务内部使用信号。

http://docs.python.org/library/signal.html