Julia 1.3 threaded write InexactError

[scottstanie]

I can't seem to save different files while in a threaded for loop:

julia> using JLD2

julia> function f1()
       function innerwrite(layer, i)
           jldopen("testwrite$i.jld2", "w") do f
               write(f, "stack", layer)
               println("writing testwrite$i on thread $(Threads.threadid())")
           end
       end
       rr = rand(800, 800, 5);
       Threads.@threads for i = 1:size(rr, 3)
           layer = rr[:, :, i]
           innerwrite(layer, i)
       end
       end
f1 (generic function with 1 method)

julia> f1()
writing testwrite4 on thread 3
writing testwrite5 on thread 4
writing testwrite1 on thread 1
writing testwrite2 on thread 1
ERROR: InexactError: trunc(UInt32, -1320009088)
Stacktrace:
 [1] wait(::Task) at ./task.jl:221
 [2] macro expansion at ./threadingconstructs.jl:75 [inlined]
 [3] f1() at ./REPL[2]:9
 [4] top-level scope at REPL[3]:1

julia> versioninfo()
Julia Version 1.3.0-alpha.0
Commit 6c11e7c2c4 (2019-07-23 01:46 UTC)
Platform Info:
  OS: macOS (x86_64-apple-darwin18.6.0)
  CPU: Intel(R) Core(TM) i5-7360U CPU @ 2.30GHz
  WORD_SIZE: 64
  LIBM: libopenlibm
  LLVM: libLLVM-6.0.1 (ORCJIT, skylake)
Environment:
  JULIA_NUM_THREADS = 4

Strangely, it also seems to be having the same bug (possibly a Julia 1.3 thread bug) that allows the code to run after, but only on 1 thread.
When I test the function again:

julia> f1()
writing testwrite1 on thread 1
writing testwrite2 on thread 1
writing testwrite3 on thread 1
writing testwrite4 on thread 1
writing testwrite5 on thread 1

I opened this also in JLD JuliaIO/JLD.jl#261 and Julia JuliaLang/julia#32802 as I'm not quite sure where the problem is here.

[JeffBezanson]

t looks like this package is not thread-safe. It has a few pieces of global state. In this case I think the problem is

JLD2.jl/src/mmapio.jl

Line 278 in 4f8a35e

# simultaneously. This strategy is not thread-safe.

:

# We sometimes need to compute checksums. We do this by first calling begin_checksum when
# starting to handle whatever needs checksumming, and calling end_checksum afterwards. Note
# that we never compute nested checksums, but we may compute multiple checksums
# simultaneously. This strategy is not thread-safe.

const CHECKSUM_POS = Int64[]
const NCHECKSUM = Ref{Int}(0)

[JonasIsensee]

AFAICT there are two places that are not threadsafe.
the above plus a global list of currently open files.

The open file list could easily be made safe with a lock
but the checksum list..
In my view this shouldn't live in the main scope.
Maybe it could be moved into an additional field of theJLDFile

[JonasIsensee]

Opened as a general feature request in #200