How to use global variable in python, in a threadsafe way

Question

I want to use a global variable, Init it once. having a thread safe access.

Can someone share an example please?

Googled python variable scope. First link : http://www.saltycrane.com/blog/2008/01/python-variable-scope-notes/ — Achrome, Feb 20 '13 at 12:00
What do you mean by thread safe? http://blogs.msdn.com/b/ericlippert/archive/2009/10/19/what-is-this-thing-you-call-thread-safe.aspx — David Heffernan, Feb 20 '13 at 12:02

score 6 · Answer 1 · answered Feb 20 '13 at 12:06

If you need read-only access and the value is initialized before threads are spawn, you don't need to worry about thread safety.

If that is not the case Python threading library is probably what you need, more precisely locks. A really good read on the subject - http://effbot.org/zone/thread-synchronization.htm with quite a lot of examples.

score 1 · Answer 2 · answered Feb 20 '13 at 12:25

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You do have a problem if you are using multiprocessing.Processes. In which case you should take a look at Managers and Queues in the multiprocessing module.

answered Feb 20 '13 at 12:25

owobeid

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score 1 · Answer 3 · answered Nov 15 '20 at 10:33

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The threading library is what you want:

import threading
mydata = threading.local()
mydata.x = 1

answered Nov 15 '20 at 10:33

Rune Kaagaard

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score 0 · Answer 4 · answered Feb 20 '13 at 12:45

If you initialize it once, and if you initialize it on when module is loaded (that means: before it can be accessed from other threads), you will have no problems with thread safety at all. No synchronization is needed.

But if you mean a more complex scenario, you have to explain it further to get a reasonable code example.

How to use global variable in python, in a threadsafe way

4 Answers4