WoWInterface - View Single Post - Threads: where is the mutex/lock api?
View Single Post
09-26-20, 04:11 AM   #1
A Murloc Raider
AddOn Author - Click to view addons
Join Date: Sep 2020
Posts: 8
Threads: where is the mutex/lock api?

I have just noticed some problems that have the hallmark race conditions. I have two functions, both called via an event. One of them I just added and it is essentially called every 3 seconds. The other is called based on an in game event, GROUP_ROSTER_UPDATE. Both of these functions call another which iterates over the group. I had noticed various errors around the return from GetRaidRosterInfo() being nil, which while its annoying that there is no interface to get a static representation of the group, can be explained by those group events like join/leave happening asynchronously and I just having the ability to iterate over an ever changing group. Bad, but explainable.

Now, when I really started to think I might be getting called by more than one thread, is when I got an index nil error for something that had just been returned by pair(). e.g.

  findWaitingPlayerIdx = function(self, player)
    for i, wait in pairs(self.waiting) do
      if wait[1] == player then
        return i
    return nil
self.waiting is core, so anything that has accessed it or changed it up to now has been hit pretty hard. What has changed was the function that enumerates groups started calling in to functions like the above, one of which removes an item from the list, and also started being called by two different event paths.

So, after that not so brief introduction, can anyone tell me categorically that wow either does or does not call events on multiple threads, and if it doesn't then I will go scratch my head some more and be glad I don't have the problem I think I might.

But if it it does, how am I to deal with that when the mutexess etc. are not included in the wow version of Lua. I've stumbled upon something that implements a mutex like thing, but without atomic operations that need support and guarantees from the silicon it can only help to reduce the window of a race condition, not eliminate it.

  Reply With Quote