Is this deque thread-safe in python?

python thread-safety deque
user1102018 picture user1102018 · Dec 18, 2011 · Viewed 21k times · Source

I can't decide whether the following deque is thread-safe.
In short, I've created a class with a deque that displays its contents every 1 sec in a new thread (so it won't pause the main program while printing).
The deque is filled from the main thread, so basically there SHOULD be a chance of collision.
HOWEVER, the deque is filled using a class method, so essentially it is accessed from within the instance itself, therefore from the same thread.
Here's the simplified code:

import threading
import time
from collections import deque

class MyQueue(threading.Thread):
    def __init__(self):
        threading.Thread.__init__(self)
        self.q = deque()
        self.start()

    def run(self):
        # pop out queue items every 1 sec
        # (please ignore empty deque for now)
        while True:
            print self.q.popleft()
            time.sleep(1)

    def add_to_q(self, val):
        # this function is called from outside
        self.q.append(val)

# main
# fill the queue with values
qu = MyQueue()
for i in range(1:100):
    qu.add_to_q(i)

So, although adding and removing items from queue take place inside the instance, is there a risk due to the adding function being called from outside the instance?

EDIT:
Since I need to modify items in my deque, I had to use Deque. What I do is: roatate() to the given item, pop it out, modify, push it back in and rotate() it back to its original position.
Unless I find a way of implementing modifying items in a Queue, I'll have to stick to Deque

Answer

King picture King · Dec 18, 2011

Deque is thread-safe (http://docs.python.org/library/collections.html#deque-objects) for appends and pops from opposite sides. Beneath here, the docs only mention that append() and popleft() are thread-safe.

There is a thread-safe implementation of the Queue itself. So you should be using it unless you have some strange requirements.

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