threading.Condition vs threading.Event

Parker Ault picture Parker Ault · Sep 15, 2011 · Viewed 12.7k times · Source

I have yet to find a clear explanation of the differences between Condition and Event classes in the threading module. Is there a clear use case where one would be more helpful than the other? All the examples I can find use a producer-consumer model as an example, where queue.Queue would be the more straightforward solution.

Answer

donkopotamus picture donkopotamus · Sep 15, 2011

Simply put, you use a Condition when threads are interested in waiting for something to become true, and once its true, to have exclusive access to some shared resource.

Whereas you use an Event when threads are just interested in waiting for something to become true.

In essence, Condition is an abstracted Event + Lock, but it gets more interesting when you consider that you can have several different Conditions over the same underlying lock. Thus you could have different Conditions describing the state of the underlying resource meaning you can wake workers that are only interested in particular states of the shared resource.