Question

I built the following code while studying about threads and queues from the following website.

from __future__ import print_function
import queue
import threading
import time

class a3_4(threading.Thread):
    q = queue.Queue()
    def __init__(self, begin, end, waiting_time):
        self.begin = begin
        self.end = end
        self.waiting_time = waiting_time
        threading.Thread.__init__(self)

    def run(self):
        while True:
            if self.begin != self.end:
                self.q.put(self.begin)
                self.begin += 1
                time.sleep(5)
            else:
                break
    def op(self):
        self.start()
        while True:
            if not self.q.empty():
                print("Outputting: ", self.q.get())
            time.sleep(self.waiting_time)

if __name__ == '__main__':
    myThread = a3_4(1, 5, 1)
    myThread.op()

I get the following output:

python3 a3_4.py 
Outputting:  1
Outputting:  2
Outputting:  3
Outputting:  4

But the program doesn't stop on its own. I tried inserting else: break but that only gives me Outputting: 1 Am I missing something very basic here?

Answer 1

I think, you are simulating producer-consumer problem. The problem is that your producer thread stops properly, but there's no termination clause for your consumer thread(main thread). So I think You need to add some termination clause for your consumer method op().

May be :

def op(self):
        self.start()
        while True:
            time.sleep(self.waiting_time)
            if not self.q.empty():
                print("Outputting: ", self.q.get())
            else:
                break

Producer-Consumer algorithm in python

1 个答案: