GC and multithreading. Strange behaviour. about julia

[gbaraldi]

I can reproduce this failure pretty reliably on my mac

[vchuravy]

Can you change:

function work(vvec)
    x = 0.0
    for v in vvec
        x += v[1]
        GC.safepoint()
    end
    return x
end

x-ref: #53441

@gbaraldi tested locally and it doesn't seem to be TTSP

[sgaure]

I see the same behaviour on my home computer (8-core AMD, 16 virtual, 32GB).

I've added the GC.safepoint(). It then runs a little bit slower, but exhibits the same behaviour. I added a GC.enable_logging() just before the final loop, and get output like this:

GC: pause 2.47ms. collected 2.212631MB. incr 
Heap stats: bytes_mapped 128.03 MB, bytes_resident 125.77 MB,
heap_size 2396.50 MB, heap_target 2857.47 MB, Fragmentation 0.676
parallel: 2.907488 seconds (3.46 k allocations: 763.115 MiB, 0.09% gc time, 0.57% compilation time)

GC: pause 54606.31ms. collected 0.175213MB. incr 
Heap stats: bytes_mapped 128.03 MB, bytes_resident 125.77 MB,
heap_size 3159.47 MB, heap_target 4578.44 MB, Fragmentation 0.754
parallel: 57.575935 seconds (9 allocations: 762.940 MiB, 94.84% gc time)
parallel: 2.794884 seconds (9 allocations: 762.940 MiB)

GC: pause 111046.63ms. collected 0.003555MB. incr 
Heap stats: bytes_mapped 128.03 MB, bytes_resident 125.77 MB,
heap_size 4685.34 MB, heap_target 6295.01 MB, Fragmentation 0.671
parallel: 113.891304 seconds (9 allocations: 762.940 MiB, 97.50% gc time)
parallel: 2.858441 seconds (9 allocations: 762.940 MiB)
parallel: 2.933410 seconds (9 allocations: 762.940 MiB)

GC: pause 109319.78ms. collected 2288.825127MB. full 
Heap stats: bytes_mapped 128.03 MB, bytes_resident 125.77 MB,
heap_size 4685.34 MB, heap_target 6581.12 MB, Fragmentation 0.997
parallel: 112.186802 seconds (9 allocations: 762.940 MiB, 97.44% gc time)
parallel: 2.859512 seconds (9 allocations: 762.940 MiB)
parallel: 2.884207 seconds (9 allocations: 762.940 MiB)

GC: pause 111792.86ms. collected 2670.297150MB. incr 
Heap stats: bytes_mapped 128.03 MB, bytes_resident 125.77 MB,
heap_size 4303.84 MB, heap_target 6199.61 MB, Fragmentation 1.085
parallel: 114.707073 seconds (9 allocations: 762.940 MiB, 97.46% gc time)