Program hangs on GC activity

[PallHaraldsson]

Program from #45369 sometimes hangs (likely in any version), at least on Linux.

See: https://discourse.julialang.org/t/hang-on-1-6-6-1-7-0-julia-1-8-0-beta3-and-1-9/83752

[KristofferC]

Running

using Dates

const mem_size = 0x1_000_000

counter = let
    counter = 0
    start_t = now()

    while true
        dt =  Dates.second(now()) - Dates.second(start_t)
        dt > 15 && break
        if counter % 1000 == 0
            println("dt: $dt, counter: $counter")
        end
        counter += 1
        arr = Vector{Int32}(undef, mem_size)
        arr[rand(1:mem_size)] = rand(Int32, 1)[begin]
        # sleep(1)
    end
    counter
end

@show counter, mem_size

it shows:

dt: 11, counter: 415000
dt: 11, counter: 416000
dt: 11, counter: 417000
dt: 11, counter: 418000
dt: 11, counter: 419000
dt: 11, counter: 420000
dt: -48, counter: 421000
dt: -48, counter: 422000
dt: -48, counter: 423000

So it is clear that the script is just having a bug in how it calculates the elapsed time (not considering the wrapping of Dates.second(now())).

[PallHaraldsson]

@gbaraldi or whoever, please drop GC label (I think I can't). Still, thanks for adding it... That was a wild-goose chase... never about allocation even (as I had discovered), only a bad idiom, I copy-pasted from @rssdev10's PR.

[rssdev10]

a bad idiom, I copy-pasted from @rssdev10's PR.

Actually, that works, but 45 seconds per minute only....

Thanks, fixed.