CODEWITHSUNDEEP
pythonmultithreadingconcurrencypython-2.x
Henrik Gustafsson
Henrik Gustafsson

Reputation: 54188

Keyboard interruptable blocking queue in Python

It seems

import Queue

Queue.Queue().get(timeout=10)

is keyboard interruptible (ctrl-c) whereas

import Queue

Queue.Queue().get()

is not. I could always create a loop;

import Queue
q = Queue()

while True:
    try:
        q.get(timeout=1000)
    except Queue.Empty:
        pass

but this seems like a strange thing to do.

So, is there a way of getting an indefinitely waiting but keyboard interruptible Queue.get()?

Upvotes: 12

Views: 3980

Answers (2)

Anders Waldenborg
Anders Waldenborg

Reputation: 3035

This may not apply to your use case at all. But I've successfully used this pattern in several cases: (sketchy and likely buggy, but you get the point).

STOP = object()

def consumer(q):
    while True:
        x = q.get()
        if x is STOP:
            return
        consume(x)

def main()
    q = Queue()
    c=threading.Thread(target=consumer,args=[q])

    try:
        run_producer(q)
    except KeybordInterrupt:
        q.enqueue(STOP)
    c.join()

Upvotes: 4

Eli Courtwright
Eli Courtwright

Reputation: 192951

Queue objects have this behavior because they lock using Condition objects form the threading module. So your solution is really the only way to go.

However, if you really want a Queue method that does this, you can monkeypatch the Queue class. For example:

def interruptable_get(self):
    while True:
        try:
            return self.get(timeout=1000)
        except Queue.Empty:
            pass
Queue.interruptable_get = interruptable_get

This would let you say

q.interruptable_get()

instead of

interruptable_get(q)

although monkeypatching is generally discouraged by the Python community in cases such as these, since a regular function seems just as good.

Upvotes: 6

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