Example on Threads in README results in deadlocks

[OkonSamuel]

The following example from README results in hanging for n>=70 using 4 Threads

n = 10
p = Progress(n)
tasks = Vector{Task}(undef, n)
for i in 1:n
    tasks[i] = Threads.@spawn begin
        sleep(2*rand())
        next!(p)
    end
end
wait.(tasks)

[IanButterworth]

I can't replicate this locally, but it might be that we should be using ReentrantLock over SpinLock. I've heard mentions that ReentrantLocks should basically always be used over SpinLocks since we added this functionality.

@OkonSamuel can you try out #153 and see if that fixes it for you?

[OkonSamuel]

@ianshmean Thanks. I'll check it out

[OkonSamuel]

It now works. Thanks.
PS: Although sometimes the display is distorted and other times its fine.

[IanButterworth]

Great, I'm going to re-open the issue so that it gets closed when that PR merges