time.sleep() function

Question

I am just trying to understand that if when I call time.sleep(x), the current thread that is running the code gets delayed by x seconds. But does that free up the processor for those x seconds or does the thread keep the resources to itself and after x seconds it just starts executing the next lines of code.

Editing with the exact scenario I am facing:

Here's the case with me:

class SomeHandler(tornado.websocket.WebSocketHandler)
  @tornado.gen.coroutine
  def something_async():
    time.sleep(5)
    return result

  def on_message(message):
    future = yield something_async(message)

if __name__ == '__main__':
  application = tornado.web.Application([
    (r'/', SomeHandler),
  ])

  http_server = tornado.httpserver.HTTPServer(application)
  http_server.listen(8888)
  tornado.ioloop.IOLoop.instance().start()

Now since this Tornado will be a single threaded server, What exactly does time.sleep(5) do in this case (will it just block the thread for 5 seconds making the whole process synchronous) or the coroutine spawns a new thread?

Answer 1

An example is always best:

#!/usr/bin/env python
# -*- coding: utf-8; py-indent-offset:4 -*-
###############################################################################
from __future__ import (absolute_import, division, print_function)
#                        unicode_literals)

import threading
import time


def func1():
    time.sleep(10)
    print('Func1: Out of sleep and returning')


def func2(flag):
    while not flag:
        time.sleep(1)
        print('Func2: looping')

    print('Func2: Flag set, leaving')


t1 = threading.Thread(target=func1)
f = list()

t2 = threading.Thread(target=func2, kwargs=dict(flag=f))

t1.start()
t2.start()

t1.join()
f.append(None)

With output:

Func2: looping
Func2: looping
Func2: looping
Func2: looping
Func2: looping
Func2: looping
Func2: looping
Func2: looping
Func2: looping
Func1: Out of sleep and returning
Func2: looping
Func2: Flag set, leaving

It should be obvious from the output that even if t1 (the 1st thread) is blocked in a long time.sleep of 10 seconds, the 2nd thread t2 is running.

And even when t1 is done we see that the main thread is able to append to the list which is being used as a flag to let t2 understand it has to return and therefore end.

So: time.sleep only blocks the thread in which is being executed.

Answer 2

Tornado never spawns a thread for you.* If you call time.sleep, it blocks the entire process for the duration of the sleep; no other processing proceeds. This is why the docs say "time.sleep should not be used in coroutines because it is blocking" . To explicitly pause a coroutine and return control to the IOLoop so other processing can proceed:

yield gen.sleep(0.5)

* Tornado can spawn threads for DNS resolution or when you explicitly use a ThreadPoolExecutor to make a task asynchronous. But you can ignore these cases for this discussion.

Answer 3

you can use the code inside function:

import time
time.sleep(2) # put value here as seconds, 2 is 2 seconds

OR

from time import sleep
sleep(60) # put value here as seconds, 60 is 60 seconds = 1 minute

Example code:

import time
def function1():
    print('function1 is sleeping for 2 seconds...')
    time.sleep(2)

count = 0
while True:
    if count >= 10:
        break
    function1()
    count=count+1

For further details please visit: https://docs.python.org/3/library/time.html#time.sleep