我也有兴趣了解为什么链不适用于失败的任务。
我挖掘了一些芹菜代码,到目前为止我发现的是:
实现发生在 app.builtins.py
@shared_task
def add_chain_task(app):
from celery.canvas import chord, group, maybe_subtask
_app = app
class Chain(app.Task):
app = _app
name = 'celery.chain'
accept_magic_kwargs = False
def prepare_steps(self, args, tasks):
steps = deque(tasks)
next_step = prev_task = prev_res = None
tasks, results = [], []
i = 0
while steps:
# First task get partial args from chain.
task = maybe_subtask(steps.popleft())
task = task.clone() if i else task.clone(args)
i += 1
tid = task.options.get('task_id')
if tid is None:
tid = task.options['task_id'] = uuid()
res = task.type.AsyncResult(tid)
# automatically upgrade group(..) | s to chord(group, s)
if isinstance(task, group):
try:
next_step = steps.popleft()
except IndexError:
next_step = None
if next_step is not None:
task = chord(task, body=next_step, task_id=tid)
if prev_task:
# link previous task to this task.
prev_task.link(task)
# set the results parent attribute.
res.parent = prev_res
results.append(res)
tasks.append(task)
prev_task, prev_res = task, res
return tasks, results
def apply_async(self, args=(), kwargs={}, group_id=None, chord=None,
task_id=None, **options):
if self.app.conf.CELERY_ALWAYS_EAGER:
return self.apply(args, kwargs, **options)
options.pop('publisher', None)
tasks, results = self.prepare_steps(args, kwargs['tasks'])
result = results[-1]
if group_id:
tasks[-1].set(group_id=group_id)
if chord:
tasks[-1].set(chord=chord)
if task_id:
tasks[-1].set(task_id=task_id)
result = tasks[-1].type.AsyncResult(task_id)
tasks[0].apply_async()
return result
def apply(self, args=(), kwargs={}, **options):
tasks = [maybe_subtask(task).clone() for task in kwargs['tasks']]
res = prev = None
for task in tasks:
res = task.apply((prev.get(), ) if prev else ())
res.parent, prev = prev, res
return res
return Chain
您可以看到最后prepare_steps
prev_task
链接到下一个任务。当 prev_task 失败时,不会调用下一个任务。
我正在测试将 prev 任务中的 link_error 添加到下一个任务:
if prev_task:
# link and link_error previous task to this task.
prev_task.link(task)
prev_task.link_error(task)
# set the results parent attribute.
res.parent = prev_res
但是,下一个任务必须处理这两种情况(也许,除非它被配置为不可变,例如不接受更多参数)。
我认为链可以通过允许一些这样的语法来支持这一点:
c = chain(t1, (t2, t1e), (t3, t2e))
意思是:
t1
link
去t2
和link_error
去t1e
t2
link
去t3
和link_error
去t2e