Setting Cache from background process in Flask

Question

I'd like to set a cache variable from a background process in Flask using its SimpleCahce framework. That is:

from rq import Queue
from worker import conn
from werkzeug.contrib.cache import SimpleCache
cache = SimpleCache()

app = Flask(__name__)
q = Queue(connection=conn)

# background process to be run. located in a seperate file
def test():
    for i in range(10):
        cache.set("value", i, 3600)
        time.sleep(1)

@app.route('/')
def home():
    cache.clear()
    q.empty()
    q.enqueue(test, timeout=1000)
    return jsonify({'state':"running"})

@app.route('/current_value')
def get_value():
    return jsonify({'value':cache.get("value")})

However, this will always return null. I've done this before using Redis, but is setting cache in a background process not allowed with SimpleCache? Or am I just doing something wrong?

Adam Lamers · Accepted Answer · 2016-04-26 17:26:44Z

1

Werkzeug's SimpleCache isn't thread safe. It's not intended to be used by other threads or processes as it doesn't implement locking.

Also, the documentation seems to allude to the cache being stored in process memory, which would make it quite difficult to alter the main process's cache from a secondary one.

answered Apr 26, 2016 at 17:26

Adam Lamers

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2 Comments

Ben Over a year ago

Do you know a recommended (and simple) caching method that is thread safe?

Adam Lamers Over a year ago

If you're going to need to modify the cache from multiple processes, you should use a dedicated cache server like Redis, it will save you a lot of headaches.

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