Getting error "OSError: [Errno 98] Address already in use" when making lots of requests.

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I am making tons of requests at one time, for example say 100k. I am using a semaphore to limit the requests, but I'm still getting the address already in use error.

I am pretty sure the answer lies in setting SO_REUSEPORT or SO_REUSEADDR somewhere, but I'm not 100% sure where to do this. I'm using asyncio and uvloop to make these requests with async_dns. If you can help me I'd appreciate it! THANKS!

Here is the (very rough) code:

import asyncio
import uvloop
from async_dns.resolver import ProxyResolver
from async_dns import types

tasks = []
asyncio.set_event_loop_policy(uvloop.EventLoopPolicy())
resolver = ProxyResolver()

async def lookup(name):
    with (await sem):
        response = await resolver.query(name, types.A)
        try:
            if response.__dict__['an']:
                print(response)
        except AttributeError:
            pass

with open('subdomains.txt') as f:
    names = f.read().splitlines()

print("Looking up {} subdomains...".format(len(names)))

for n in names:
    task = asyncio.ensure_future(lookup('{}.testdomain.com'.format(n)))
    tasks.append(task)

sem = asyncio.Semaphore(500)
loop = asyncio.get_event_loop()
loop.run_until_complete(asyncio.wait(tasks))

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Running the code above now results in

AttributeError: 'NoneType' object has no attribute 'an'

I believe that all requests for domains that don't exist now result in the same error...