Fatal error on multi-threaded code processing image files #32939
Description
The following script processes a couple of images with some file I/O. Running it with @threads causes a failure. It always breaks when calling the script directly with JULIA_NUM_THREADS>1 , though when includeing it in a running session it seems it breaks the first time and later it works.
Am I wrong in assuming this code is thread-safe in the first place, or could this be a bug somewhere?
using FileIO
using Images
imgs = [
"https://images.unsplash.com/photo-1554266183-2696fdafe3ff?ixlib=rb-1.2.1&auto=format&fit=crop&w=564&q=80"
"https://images.unsplash.com/photo-1527026950045-9e066846bae4?ixlib=rb-1.2.1&ixid=eyJhcHBfaWQiOjEyMDd9&auto=format&fit=crop&w=1419&q=80"
"https://images.unsplash.com/photo-1549287748-f095932c9f81?ixlib=rb-1.2.1&ixid=eyJhcHBfaWQiOjEyMDd9&auto=format&fit=crop&w=606&q=80"
"https://images.unsplash.com/photo-1437448317784-3a480be9571e?ixlib=rb-1.2.1&ixid=eyJhcHBfaWQiOjEyMDd9&auto=format&fit=crop&w=634&q=80"
]
files = download.(imgs)
Threads.@threads for f in files
a = load(f)
r = rand(eltype(a), size(a)...)
a .= map(clamp01nan, a + 0.5*r)
save(f*".png", a)
endThe error:
$ JULIA_NUM_THREADS=4 julia mycode.jl
Error encountered while loading "/tmp/jl_5OG85C".
Fatal error:
Error encountered while loading "/tmp/jl_hZpwGF".
Fatal error:
Error encountered while loading "/tmp/jl_BlmZ9H".
Fatal error:
ERROR: LoadError: concurrency violation detected
Stacktrace:
[1] try_yieldto(::typeof(Base.ensure_rescheduled), ::Base.RefValue{Task}) at ./task.jl:552
[2] wait() at ./task.jl:609
[3] wait(::Base.GenericCondition{Base.Threads.SpinLock}) at ./condition.jl:107
[4] wait(::Task) at ./task.jl:214
[5] top-level scope at ./threadingconstructs.jl:75
[6] include at ./boot.jl:328 [inlined]
[7] include_relative(::Module, ::String) at ./loading.jl:1094
[8] include(::Module, ::String) at ./Base.jl:31
[9] exec_options(::Base.JLOptions) at ./client.jl:295
[10] _start() at ./client.jl:468
in expression starting at /home/user/src/julia-test/mycode.jl:13
julia> versioninfo()
Julia Version 1.3.0-alpha.1
Commit f2513a8ca6* (2019-07-23 05:06 UTC)
Platform Info:
OS: Linux (x86_64-linux-gnu)
CPU: Intel(R) Core(TM) i5-8250U CPU @ 1.60GHz
WORD_SIZE: 64
LIBM: libopenlibm
LLVM: libLLVM-6.0.1 (ORCJIT, skylake)
Environment:
JULIA_NUM_THREADS = 4
JULIA_EDITOR = emacsclient