blpop will not receive any data if the key empty for a long time and then pushed a data

[kingname]

Version: What redis-py and what redis version is the issue happening on?

• redis-py: 3.2.1
• redis: 5.0

Platform: What platform / version? (For example Python 3.5.1 on Windows 7 / Ubuntu 15.10 / Azure)

• Ubuntu 18.04
• Python 3.7.3

Description: Description of your issue, stack traces from errors and code that reproduces the issue

while True:
    data = client.blpop('key')[1]
    print(data)

this code will work normally when I launch it just now. but if the list keeps empty for a long time, for example, 2 days, and then I push a data to it. this code will still blocked at data = client.blpop('key')[1]，could not receive any data. only after I terminal the process and relaunch it again, it can receive the new data.

[andymccurdy]

Sounds like something on your network is killing the idle connection. And unfortunately the health check improvements in 3.3.x won't work in this case because we cannot send a health check in the middle of a blocking statement.

However you could pass a timeout to BRPOP. You'd just need to account for BRPOP returning None in the case the code hits the timeout.

[kingname]

Thanks for your reply.

So, if I pass a timeout, such as 5 minutes, and then, if I receive the data in 5 minutes, I parse it. if I don't, I parse the timeout logic, and then blpop again.

[andymccurdy]

If you call data = client.blpop('key', timeout=300), the code will block until either a value is pushed on to the key list or 300 seconds passes. If 300 seconds pass, None will be returned.

[captainst]

Got similar issue. I am using redis-py to get the keys from a remote redis server (over internet). I am using the code like:

while True:
    queue = db.blpop('detection_queue', timeout=5)
    if queue is not None:
        # process the queue

If the queue is empty, activity idle, without the timeout param, the process becomes dead (db.blpop never returned) after about 20 minutes.
Adding the timeout=5 seems to help quite a bit, but I still observed that the process is dead after about 9~10 hours of idle.

[andymccurdy]

@captainst this seems like a separate issue. If you want to open another issue with details including your redis-py version and connection string I can take a look.

[captainst]

@andymccurdy Thank you for the fast reply. I'll do it.