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@p7k
Created Dec 8, 2012
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greenlet throttling decorator | rate limiting gevent | with semaphores
from functools import wraps
from timeit import default_timer
import gevent
from gevent.queue import Queue
def gevent_throttle(calls_per_sec=0):
"""Decorates a Greenlet function for throttling."""
interval = 1. / calls_per_sec if calls_per_sec else 0
def decorate(func):
blocked = [False] # has to be a list to not get localised inside the while loop
# otherwise, UnboundLocalError: local variable 'blocked' referenced before assignment
last_time = [0] # ditto
@wraps(func) # propagates docstring
def throttled_func(*args, **kwargs):
while True:
# give other greenlets a chance to run, otherwise we
# might get stuck while working thread is sleeping and the block is ON
gevent.sleep(0)
if not blocked[0]:
blocked[0] = True
# check if actually might need to pause
if calls_per_sec:
last, current = last_time[0], default_timer()
elapsed = current - last
if elapsed < interval:
gevent.sleep(interval - elapsed)
last_time[0] = default_timer()
blocked[0] = False
return func(*args, **kwargs)
return throttled_func
return decorate
# possible use
import requests
from gevent.pool import Pool
pool = Pool()
@gevent_throttle(10)
def worker(address):
"""somd doc"""
print address
url='http://maps.googleapis.com/maps/api/geocode/json'
params = dict(address=address, sensor='false')
json = requests.get(url, params=params).json
return json
jobs = pool.imap(worker, 'NYC LA SF Chicago Boston Austin Portland'.split())
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