[Tutor] Multi threading and I/O bound process

[Alan Gauld]

On 29/11/2021 01:53, Manprit Singh wrote:

> 1) Without multi threading
> 
> import time
> import urllib.request
> # a function to dsplay first 25 bytes of a webpage
> def readpage(urladd):
>     with urllib.request.urlopen(urladd) as fobj:
>         print(fobj.read(25))
> 
> t0 = time.time()

Note you start the timer just before the loop after
the intialisation and function definition...

> for _ in range(6):
>     readpage("https://www.xyz.com/")
> t1 = time.time()
> print(t1-t0)
> will display the first 25 bytes of the webpage  6 times in a sequential
> order. and measure the time
> 
> 2) Multithreading Using constructor   :
> 
> t0= time.time()

Here you include the thread import and all of the initialisatoion and
class/function definitions that that includes. Not really a fair
comparison, especially on such a small scale example where every mS is
significant.

> import threading
> threadsgrp = []
> for _ in range(6):
>     thread = threading.Thread(target=readpage,args=("https://www.xyz.com/
> ",))
>     threadsgrp.append(thread)
>     thread.start()
> for th in threadsgrp:
>     th.join()
> t1 =time.time()
> print(t1-t0)
> 
> 3)  Multithreading using subclass :
> 
> t1 = time.time()

And the same here, you are including the class definition
time in the total. The init/definition code should only
run once in your program so it is not representative of
the time that threading/non-threading takes in a real
work program where threading is called many times in
different places.

> class Techlivethread(threading.Thread):
>     def __init__(self, add):
>         threading.Thread.__init__(self)
>         self.add = add
>     def run(self):
>         readpage(self.add)

It would be more efficient to transfer the readpage
code into run() directly since all you do is call it.

> grp =[]
> for _ in range(6):
>     th1 = Techlivethread("https://www.xyz.com/")
>     grp.append(th1)
>     th1.start()
> for ele in grp:
>     ele.join()
> t2 = time.time()
> print(t2-t1)



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Alan G
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