Anything wrong in my Producer-Consumer implementation in Python using condition objects?

Question

Can someone let me know what is wrong in my code below that implements the producer-consumer problem in python. I am using Python 3.4

import threading
from threading import Thread
from collections import deque
import time

maxSize = 4    # maximum size of the queue
q = deque([])
cur = 0    # current value to push into the queue

lk = threading.Lock()
cvP = threading.Condition(lk)    # condition object for consumer
cvC = threading.Condition(lk)    # condition object for producer

class Producer:
    def run(self):
        global maxSize, q, cur
        while True:
            with cvP:
                while len(q) >= maxSize:
                    print( "Queue is full and size = ", len(q) )
                    cvC.notify()   # notify the Consumer
                    cvP.wait()    # put Producer to wait

                q.append(cur)
                print("Produced ", cur)
                cur = cur + 1
                cvC.notify()    # notify the Consumer


class Consumer:
    def run(self):
        global maxSize, q, cur
        while True:
            with cvC:
                while len(q) == 0:
                    print( "Queue is empty and size = ", len(q) )
                    cvP.notify()  # notify the Producer
                    cvC.wait()    # put Consumer to wait

                x = q.popleft()
                print("Consumed ", x)
                time.sleep(1)
                cvP.notify()    # notify the Producer

p = Producer()
c = Consumer()
pThread = Thread( target=p.run(), args=())
cThread = Thread( target=c.run(), args=())
pThread.start()
cThread.start()
pThread.join()
cThread.join()

The program output:

Produced  0
Produced  1
Produced  2
Produced  3
Queue is full and size =  4

Then it got stuck. When terminating the program, I got:

Traceback (most recent call last):
  File "path/t.py", line 47, in <module>
    pThread = Thread( target=p.run(), args=())
  File "path/t.py", line 22, in run
    cvP.wait()
  File "/usr/lib/python3.4/threading.py", line 289, in wait
    waiter.acquire()
KeyboardInterrupt

The Producer seemed not "nofity" the consumer. Can someone let me know why?

Many thanks in advance!

Answer 1

The locking and unlocking are fine, but you probably want to specify 'run' as the target and not 'run()'

pThread = Thread( target=p.run, args=())
cThread = Thread( target=c.run, args=())

:-)

Explanation: lets simplify

def foo():
  # ..

# Foo will run on a new thread
Thread(target=foo)

# foo() is run before the thread is created, and its return
# value is the target for the Thread call.
Thread(target=foo())

You can see in the stack trace that it never went beyond line 47, which is

pThread = Thread( target=p.run(), args=())

Which is the same as

x = p.run()
pThread = Thread(x, args=())