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Multi-worker pipeline and closable queue

Project Description

Multi-worker pipelines with gevent.


import gevent
import random

from itertools import repeat
from gevent_pipeline import Pipeline

def sample(b):
    r = random.uniform(0, b)
    return r

    .from_iter(repeat(1, times=200))
    .map(sample, n_workers=100)
    .filter(lambda x: x < 0.5)
    .reduce(max, x0=0, n_workers=50))


Chain together operations with multiple workers for each layer.


>>> import operator
>>> def only_odd(x):
...     return x & 1
>>> def double(x):
...     return 2 * x
>>> (Pipeline()
...         .from_iter(range(100))
...         .filter(only_odd, n_workers=10)
...         .map(double, n_workers=8)
...         .reduce(operator.add, x0=0, n_workers=5))

The above is functionally equivalent to:

>>> @worker(discard_none=True)
... def only_odd(x):
...     '''Forward only odd numbers to the next layer'''
...     if x & 1:
...        return x
>>> @worker()
... def double(x):
...     return 2 * x
>>> def load_numbers(q_in, q_out, q_done):
...     for i in range(100):
...         q_out.put(i)
...     q_done.put(None)
>>> q_out = ClosableQueue()
>>> p = (Pipeline()
...     .chain_workers(load_numbers)
...     .chain_workers(only_odd, n_workers=10)
...     .chain_workers(double, n_workers=8, q_out=q_out))
>>> sum(i for i in q_out)

There is no guarantee of order:

>>> def f(x):
...     gevent.sleep(random.uniform(0, 0.001))
...     return x
>>> p = Pipeline().from_iter(range(10)).map(f, n_workers=5)
>>> list(p)
[2, 1, 4, 0, 3, 5, 8, 6, 7, 9]

Exceptions in workers

There is a predefined forward_input exception handler, in the event the function raises an exception the handler takes the input to the function and passes it along as if it was the output.

from gevent_pipeline import Pipeline, worker, forward_input

def f(x):
    if x & 1:
        raise ValueError("oh no!")
        # Will be treated as if it were:
        # return x
        return 2 * x

p = (Pipeline()
     .chain_workers(f, n_workers=10))

s_odd = sum(range(1, 100, 2))
s_even = sum(2*i for i in range(0, 100, 2))
assert sum(p) == s_odd + s_even


Acts like gevent.queue.Queue but in addition has a .close() method which invokes following behavior:

  • Calling .put(item) becomes an error
  • Successive calls to .get() will return whatever remains in the queue and after that StopIteration is returned for every subsequent call
>>> from gevent_pipeline import ClosableQueue
>>> q = ClosableQueue()
>>> q.put('hello')
>>> q.close()
>>> q.get()
>>> q.get() is StopIteration

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