I'm working on a project that parses data from a lot of websites. Most of my code is done, so i'm looking forward to use asyncio in order to eliminate that I/O waiting, but still i wanted to test how threading would work, better or worse. To do that, i wrote some simple code to make requests to 100 websites. Btw i'm using requests_html library for that, fortunately it supports asynchronous requests as well.
asyncio code looks like:
import requests
import time
from requests_html import AsyncHTMLSession
aio_session = AsyncHTMLSession()
urls = [...] # 100 urls
async def fetch(url):
try:
response = await aio_session.get(url, timeout=5)
status = 200
except requests.exceptions.ConnectionError:
status = 404
except requests.exceptions.ReadTimeout:
status = 408
if status == 200:
return {
'url': url,
'status': status,
'html': response.html
}
return {
'url': url,
'status': status
}
def extract_html(urls):
tasks = []
for url in urls:
tasks.append(lambda url=url: fetch(url))
websites = aio_session.run(*tasks)
return websites
if __name__ == "__main__":
start_time = time.time()
websites = extract_html(urls)
print(time.time() - start_time)
Execution time (multiple tests):
13.466366291046143
14.279950618743896
12.980706453323364
BUT
If i run an example with threading:
from queue import Queue
import requests
from requests_html import HTMLSession
from threading import Thread
import time
num_fetch_threads = 50
enclosure_queue = Queue()
html_session = HTMLSession()
urls = [...] # 100 urls
def fetch(i, q):
while True:
url = q.get()
try:
response = html_session.get(url, timeout=5)
status = 200
except requests.exceptions.ConnectionError:
status = 404
except requests.exceptions.ReadTimeout:
status = 408
q.task_done()
if __name__ == "__main__":
for i in range(num_fetch_threads):
worker = Thread(target=fetch, args=(i, enclosure_queue,))
worker.setDaemon(True)
worker.start()
start_time = time.time()
for url in urls:
enclosure_queue.put(url)
enclosure_queue.join()
print(time.time() - start_time)
Execution time (multiple tests):
7.476433515548706
6.786043643951416
6.717151403427124
The thing that i don't understand .. both libraries are used against I/O problems, but why are threads faster ? The more i increase the number of threads, the more resources it uses but it's a lot faster.. Can someone please explain to me why are threads faster than asyncio in my example ?
Thanks in advance.