Concurrent PRAW Instances

By default, PRAW works great when there is a one-to-one mapping between running PRAW processes, and the IP address / user account that you make requests from. In fact, as of version 2.1.0, PRAW has multithreaded support as long as there is a one-to-one mapping between thread and PRAW Reddit object instance. That is, in order to be thread safe, each thread needs to have its own Reddit instance [1]. In addition to multithreaded rate-limiting support, PRAW 2.1.0 added multiprocess rate limiting support.

[1]	It is undetermined at this time if the same authentication credentials can be used on multiple instances where the modhash is concerned.

praw-multiprocess

PRAW version 2.1.0 and later install with a program praw-multiprocess. This program provides a request handling server that manages the rate-limiting and caching of any PRAW process which directs requests toward it. Starting praw-multiprocess is as simple as running praw-multiprocess from your terminal / command line assuming you installed PRAW properly.

By default praw-multiprocess will listen only on localhost port 10101. You can adjust those settings by passing in --addr and --port arguments respectively. For instance to have praw-multiprocess listen on all valid addresses on port 65000, execute via: praw-multiprocess --addr 0.0.0.0 --port 65000. For a full list of options execute praw-multiprocess --help.

PRAW’s MultiprocessingHandler

In order to interact with a praw-multiprocess server, PRAW needs to be instructed to use the MultiprocessHandler rather than the DefaultHandler. In your program you need to pass an instance of MultiprocessHandler into the handler keyword argument when creating the Reddit instance. Below is an example to connect to a praw-multiprocess server running with the default arguments:

import praw
from praw.handlers import MultiprocessHandler

handler = MultiprocessHandler()
r = praw.Reddit(user_agent='a descriptive user-agent', handler=handler)

With this configuration, all network requests made from your program(s) that include the above code will be proxied through the praw-multiprocess server. All requests made through the same praw-multiprocess server will respect reddit’s API rate-limiting rules

If instead, you wish to connect to a praw-multiprocess server running at address 10.0.0.1 port 65000 then you would create the PRAW instance via:

import praw
from praw.handlers import MultiprocessHandler

handler = MultiprocessHandler('10.0.0.1', 65000)
r = praw.Reddit(user_agent='a descriptive user-agent', handler=handler)

PRAW Multiprocess Resiliency

With all client/server type programs there is the possibility of network issues or simply a lack of an available server. PRAW’s MultiprocessHandler was created to be quite resilient to such issues. PRAW will retry indefinitely to connect to praw-multiprocess server. This means that a praw-multiprocess server can be stopped and restarted without any effect on programs utilizing it.

On the other hand, consecutive network failures where the MultiprocessHandler has no issue establishing a connection to a praw-multiprocess server will result in ClientException after three failures. Such failures are not expected to occur and if reproducable should be reported.