multi-threading and lambda variable scope

Question

I am using a class that manages a pool of threads to run actions. Originally it was coded to take an Action (with no parameter) and I was calling it like this:

Answer 1

So the problem is that you're closing over variables that you don't mean to. The easy fix in most all cases is to create a new local variable, copy the variable you were once closing over, and then close over that instead.

So instead of:

for(int i = 0; i < number; i++)
{
    threadPool.EnqueueTask(() => SomeMethod(someList[i]));
}

You can just do:

for(int i = 0; i < number; i++)
{
    int copy = i;
    threadPool.EnqueueTask(() => SomeMethod(someList[copy]));
}

Now each lambda is closing over it's own variable, rather than having all of them close over the same one variable.