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:
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.")
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