> On 8 Aug 2022, at 20:24, MRAB <pyt...@mrabarnett.plus.com> wrote:
>
> On 2022-08-08 12:20, Stefan Ram wrote:
>> Andreas Croci <andrea.cr...@gmx.de> writes:
>>> Basically the question boils down to wether it is possible to have parts of
>>> a program (could be functions) that keep doing their job while other parts
>>> do something else on the same data, and what is the best way to do this.
>> Yes, but this is difficult. If you ask this question here,
>> you might not be ready for this.
>> I haven't learned it yet myself, but nevertheless tried to
>> write a small example program quickly, which might still
>> contain errors because of my lack of education.
>> import threading
>> import time
>> def write_to_list( list, lock, event ):
>> for i in range( 10 ):
>> lock.acquire()
>> try:
>> list.append( i )
>> finally:
>> lock.release()
>> event.set()
>> time.sleep( 3 )
>> def read_from_list( list, lock, event ):
>> while True:
>> event.wait()
>> print( "Waking up." )
>> event.clear()
>> if len( list ):
>> print( "List contains " + str( list[ 0 ]) + "." )
>> lock.acquire()
>> try:
>> del list[ 0 ]
>> finally:
>> lock.release()
>> else:
>> print( "List is empty." )
>> list = []
>> lock = threading.Lock()
>> event = threading.Event()
>> threading.Thread( target=write_to_list, args=[ list, lock, event ]).start()
>> threading.Thread( target=read_from_list, args=[ list, lock, event ]).start()
>> In basketball, first you must learn to dribble and pass,
>> before you can begin to shoot.
>> With certain reservations, texts that can be considered
>> to learn Python are:
>> "Object-Oriented Programming in Python Documentation" - a PDF file,
>> Introduction to Programming Using Python - Y Daniel Liang (2013),
>> How to Think Like a Computer Scientist - Peter Wentworth (2012-08-12),
>> The Coder's Apprentice - Pieter Spronck (2016-09-21), and
>> Python Programming - John Zelle (2009).
> When working with threads, you should use queues, not lists, because queues
> do their own locking and can wait for items to arrive, with a timeout, if
> desired:
Lists do not need to be locked in python because of the GIL.
However you need locks to synchronise between threads.
And as you say a queue has all that locking built in.
Barry
>
>
> import queue
> import threading
> import time
>
> def write_to_item_queue(item_queue):
> for i in range(10):
> print("Put", i, "in queue.", flush=True)
> item_queue.put(i)
> time.sleep(3)
>
> # Using None to indicate that there's no more to come.
> item_queue.put(None)
>
> def read_from_item_queue(item_queue):
> while True:
> try:
> item = item_queue.get()
> except item_queue.Empty:
> print("Queue is empty; should've have got here!", flush=True)
> else:
> print("Queue contains " + str(item) + ".", flush=True)
>
> if item is None:
> # Using None to indicate that there's no more to come.
> break
>
> item_queue = queue.Queue()
>
> write_thread = threading.Thread(target=write_to_item_queue, args=[item_queue])
> write_thread.start()
>
> read_thread = threading.Thread(target=read_from_item_queue, args=[item_queue])
> read_thread.start()
>
> # Wait for the threads to finish.
> write_thread.join()
> read_thread.join()
>
> print("Finished.")
> --
> https://mail.python.org/mailman/listinfo/python-list
>
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