Global variables and threads

General Usage
1

I have a function inside a module that I need to be thread-safe. The function looks like:

function foo()
    for i=1:n
        sigma = (calculate stuff)
    end
    return sigma
end

Of course, the above code doesn’t work, because sigma is local to the for loop. So I define it as a global:

function foo()
    for i=1:n
        global sigma = (calculate stuff)
    end
    return sigma
end

Question: is the resulting global sigma local to the calling thread, or have I introduced a race condition? If the latter, what’s the idiomatic way to define the variable as local to the thread? I don’t particularly want to introduce a lock on the variable, which would introduce some inefficiency in the code.

2

Use an existing local variable, see Local scope in the Julia manual.

1 Like
3

Oh, duh. Thanks.