Writing to IOBuffer from @async/@sync

[rofinn]

Disclaimer: I'm not positive if this is an issue or just a behaviour change, but I didn't find an existing issue/topic on github or discourse.

Issue

Specifically, the following sample code seems to run fine on 0.6, but fails on a recent nightly.

using Base.Test, Compat

struct Logger
    parent::Union{Logger, Compat.Nothing}
    handle::Union{IO, Compat.Nothing}
end

io = IOBuffer()

root = Logger(nothing, io)
a = Logger(root, nothing)
b = Logger(a, nothing)

function log(logger::Logger, str)
    @async begin
        if logger.handle !== nothing
            println(logger.handle, str)
        end
    end
    if logger.parent !== nothing
        log(logger.parent, str)
    end
end

function test()
    @sync log(b, "Foo")
    @test !isempty(String(take!(io)))
end

test()

If I remove the @async on nightly then it works again.

versioninfo:

julia> versioninfo()
Julia Version 0.7.0-DEV.5214
Commit 14dbdf509a* (2018-05-24 11:25 UTC)
Platform Info:
  OS: macOS (x86_64-apple-darwin17.5.0)
  CPU: Intel(R) Core(TM) i7-5557U CPU @ 3.10GHz
  WORD_SIZE: 64
  LIBM: libopenlibm
  LLVM: libLLVM-6.0.0 (ORCJIT, broadwell)
Environment:
  JULIA_EDITOR = /usr/local/bin/atom -n
  JULIA_HISTORY = /Users/rory/.playground/share/memento/.julia_history
  JULIA_PKGDIR = /Users/rory/.playground/share/memento/packages

The above code was using Compat 0.65.0

[JeffBezanson]

This is a behavior change, from #27164. @sync now only waits for @asyncs that are lexically inside its argument expression. This is intended to make it easier to reason about what things it will wait for, and closer to the semantics of e.g. Cilk.

[rofinn]

Yep, moving the @sync into the same function solved my issue. Thanks.