芹菜:如果文档有错误，如何使用"link_error“？

Question

在芹菜文档中：http://celery.readthedocs.org/en/latest/userguide/canvas.html#chains是如何使用link_error的示例

还可以使用link_error参数添加错误回调： Add.apply_async(2，2)，link_error=log_error.s()add.subtask(2，2)，link_error=log_error.s() 由于只有在使用泡菜时才能序列化异常，因此错误回调将父任务的id作为参数： 从__future__导入print_function从proj.celery导入应用程序@app.task def log_error(task_id)：@app.task= app.AsyncResult(task_id) result.get(propagate=False) #确保结果被写入。使用open(‘/var/os.path.join’，task_id)，‘a’作为fh: print(‘-\n {1} {2}'.format( task_id，result.result，result.traceback)，file=fh)

但是在这个例子中是错误的，因为它们调用了AsuncResult.get内部任务，这导致了DEADLOCK和这个日志条目：

/opt/.virtualenvs/spark/lib/python3.4/site-packages/celery/result.py:45: RuntimeWarning: Never call result.get() within a task!
See http://docs.celeryq.org/en/latest/userguide/tasks.html#task-synchronous-subtasks

In Celery 3.2 this will result in an exception being
raised instead of just being a warning.

  warnings.warn(RuntimeWarning(E_WOULDBLOCK))

[2015-06-13 20:30:19,242: WARNING/Worker-4] /opt/.virtualenvs/spark/lib/python3.4/site-packages/celery/result.py:45: RuntimeWarning: Never call result.get() within a task!
See http://docs.celeryq.org/en/latest/userguide/tasks.html#task-synchronous-subtasks

In Celery 3.2 this will result in an exception being
raised instead of just being a warning.

  warnings.warn(RuntimeWarning(E_WOULDBLOCK))

Answer 1

请执行此检查列表以确保配置正常：

1. 必须将CELERY_IGNORE_RESULT设置为False
2. 必须设置CELERY_BACKEND_RESULT，例如'amqp' (用于RabbitMQ)
3. @task装饰器不能在每个任务上都有选项ignore_result=True (但您可以创建不变签名)

最后是为获取结果(结果)正确修改的任务：

from celery.result import allow_join_result

@app.task
def log_error(task_id):
    with allow_join_result():
        result = app.AsyncResult(task_id)
        result.get(propagate=False)  # make sure result written.
        with open(os.path.join('/var/errors', task_id), 'a') as fh:
            print('--\n\n{0} {1} {2}'.format(
                task_id, result.result, result.traceback), file=fh)

注释： result.result在ZeroDivisionError的例子中是字典：

{
    'exc_type': 'ZeroDivisionError',  # Name of Exception type
    'exc_message': 'division by zero'  # Reason of exception
}

注：

这是#2652问题，当在AsyncResult上调用get()时，芹菜忽略错误