How does io redirection work with tasks?

General Usage
,
1

I don’t understand this simple MWE:

julia> redirect_stdio(;stdout = devnull) do
           @async println("hello")
           @async redirect_io(; stdout = devnull) do
               println("hey")
           end
           println("hi")
       end
hello

The docstring of redirect_stdio doesn’t mention anything about it not affecting child tasks. How does this actually work?

3 Likes
2

The do block seems to complete without interruption, the streams restored, and then the tasks run. If you do something to interrupt the do block and go to the scheduler:

julia> redirect_stdio(;stdout = devnull) do
           @async println("hello")
           sleep(0)
           @async redirect_io(; stdout = devnull) do
               println("hey")
           end
           println("hi")
       end
3

My preference is to never let a block return if tasks created in that block are still running.

julia> Base.redirect_stdio(;stdout = devnull) do
               @sync begin
                  @async println("hello")
                  @async Base.redirect_stdio(; stdout = devnull) do
                      println("hey")
                  end
                  println("hi")
               end
              end

julia>
2 Likes