Python 如何高效地链接i并行任务并将中间结果传递给引擎?
我正在尝试在iPyParallel中将多个任务链接在一起,例如Python 如何高效地链接i并行任务并将中间结果传递给引擎?,python,ipython-parallel,Python,Ipython Parallel,我正在尝试在iPyParallel中将多个任务链接在一起,例如 import ipyparallel client = ipyparallel.Client() view = client.load_balanced_view() def task1(x): ## Do some work. return x * 2 def task2(x): ## Do some work. return x * 3 def task3(x): ## Do some w
import ipyparallel
client = ipyparallel.Client()
view = client.load_balanced_view()
def task1(x):
## Do some work.
return x * 2
def task2(x):
## Do some work.
return x * 3
def task3(x):
## Do some work.
return x * 4
results1 = view.map_async(task1, [1, 2, 3])
results2 = view.map_async(task2, results1.get())
results3 = view.map_async(task3, results2.get())
但是,除非task1完成并且基本上处于阻塞状态,否则此代码不会提交任何task2。我的任务可能需要不同的时间,而且效率很低是否有一种简单的方法可以有效地链接这些步骤,使引擎可以从前面的步骤中获得结果?类似于:
def task2(x):
## Do some work.
return x.get() * 3 ## Get AsyncResult out.
def task3(x):
## Do some work.
return x.get() * 4 ## Get AsyncResult out.
results1 = [view.apply_async(task1, x) for x in [1, 2, 3]]
results2 = []
for x in result1:
view.set_flags(after=x.msg_ids)
results2.append(view.apply_async(task2, x))
results3 = []
for x in result2:
view.set_flags(after=x.msg_ids)
results3.append(view.apply_async(task3, x))
显然,这将失败,因为AsyncResult不可拾取
我在考虑一些解决方案:
@asyncio.coroutine
def submitter(x):
result1 = yield from asyncio.wrap_future(view.apply_async(task1, x))
result2 = yield from asyncio.wrap_future(view.apply_async(task2, result1)
result3 = yield from asyncio.wrap_future(view.apply_async(task3, result2)
yield result3
@asyncio.coroutine
def submit_all(ls):
jobs = [submitter(x) for x in ls]
results = []
for async_r in asyncio.as_completed(jobs):
r = yield from async_r
results.append(r)
## Do some work, like analysing results.
它正在工作,但当引入更复杂的任务时,代码很快就会变得混乱和不直观chain
函数,该函数使用add\u done\u callback
在上一个任务完成时提交新任务,从而获得更通用的功能:
from concurrent.futures import Future
from functools import partial
def chain_apply(view, func, future):
"""Chain a call to view.apply(func, future.result()) when future is ready.
Returns a Future for the subsequent result.
"""
f2 = Future()
# when f1 is ready, submit a new task for func on its result
def apply_func(f):
if f.exception():
f2.set_exception(f.exception())
return
print('submitting %s(%s)' % (func.__name__, f.result()))
ar = view.apply_async(func, f.result())
# when ar is done, pass through the result to f2
ar.add_done_callback(lambda ar: f2.set_result(ar.get()))
future.add_done_callback(apply_func)
return f2
def chain_map(view, func, list_of_futures):
"""Chain a new callback on a list of futures."""
return [ chain_apply(view, func, f) for f in list_of_futures ]
# use builtin map with apply, since we want one Future per item
results1 = map(partial(view.apply, task1), [1, 2, 3])
results2 = chain_map(view, task2, results1)
results3 = chain_map(view, task3, results2)
print("Waiting for results")
[ r.result() for r in results3 ]
与任何add\u done\u callback
的示例一样,它可以用协同程序编写,但我发现这种情况下的回调是可以的。这至少应该是一个相当通用的实用程序,您可以使用它来编写管道
选项2:dask.distributed
全面披露:我是IPython Parallel的主要作者,我将建议您使用不同的工具
<> P>可以通过IPython并行的引擎命名空间和DAG依赖性将一个任务的结果传递给另一个任务,但是老实说,如果你的工作流程看起来像这样,你应该考虑使用它,它是专门为这种计算图设计的。如果您已经熟悉IPython parallel,那么开始使用dask应该不会有太大的负担
IPython 5.1提供了一个方便的命令,用于将IPython并行群集转换为dask分布式群集:
import ipyparallel as ipp
client = ipp.Client()
executor = client.become_distributed(ncores=1)
然后,dask的关键相关特性是,您可以将未来作为参数提交给后续的映射调用,当结果准备好时,调度程序会处理它,而不必在客户机中显式执行:
results1 = executor.map(task1, [1, 2, 3])
results2 = executor.map(task2, results1)
results3 = executor.map(task3, results2)
executor.gather(results3)
因此,基本上,dask distributed的工作方式与您希望的IPython parallel的负载平衡方式相同,当您需要这样的链接时
演示了这两个示例。在使用了这些选项之后,我认为我仍然会使用asyncio和包装类来保持代码整洁。我对dask不太熟悉,把它拖到项目中只是为了监控结果,而并行部分已经由IPyParallel完成,这感觉有些过分。
results1 = executor.map(task1, [1, 2, 3])
results2 = executor.map(task2, results1)
results3 = executor.map(task3, results2)
executor.gather(results3)