redirect_stdxxx works unexpected with Tasks or multi-threads

[cihga39871]

I found an issue that redirect_stdout fails to restore to the prior stdout when the function is calling in multiple tasks.

Background

I use Julia as the back-end server for an online website, providing bioinformatics classification service for biologists. At the back-end, the Julia server runs classification tasks with multi-threads, and collect stdout and stderr of each task in a separate log file.

However, I found some tasks are failed to output to correct log file, and sometimes Base.stdout and Base.stderr are changed to some log files.

After digging into the problem, I found redirect_stdxxx sets the global stdxxx, and is not thread save. Is is possible to create a thread safe version of those functions?

Environment

Tested in Julia 1.6.1 and 1.7.0-rc1. Version info are shown below.

Julia Version 1.7.0-rc1
Commit 9eade6195e (2021-09-12 06:45 UTC)
Platform Info:
  OS: Linux (x86_64-pc-linux-gnu)
  CPU: Intel(R) Core(TM) i9-9940X CPU @ 3.30GHz
  WORD_SIZE: 64
  LIBM: libopenlibm
  LLVM: libLLVM-12.0.1 (ORCJIT, skylake-avx512)

A small case

outfile = tempname()
outio = open(outfile, "a+")

f() = redirect_stdout(outio) do
    println(stderr, "start redirect stdout")
    sleep(20)
    println(stderr, "stop redirect stdout")
end

schedule(@task f())

@show stdout
# IOStream(<file /tmp/jl_k82o7M>)

sleep(20)
@show stdout
# Base.TTY(RawFD(13) open, 0 bytes waiting)


schedule(@task f())
sleep(2)
schedule(@task f())
@show stdout

sleep(20)
@show stdout # should be TTY, but is IOStream
# IOStream(<file /tmp/jl_k82o7M>)