@threads silently swallows errors / println() segfaults

[rened]

Errors inside the @threads macro are silently ignored. Tested with JULIA_NUM_THREADS=4.

  | | |_| | | | (_| |  |  Version 0.5.0-rc3+0 (2016-08-22 23:43 UTC)
 _/ |\__'_|_|_|\__'_|  |
|__/                   |  x86_64-apple-darwin15.6.0

julia> Threads.@threads for i = 1:10
           error()
       end

julia>

Trying to include debug outputs yields a segfault:

julia> Threads.@threads for i = 1:10
           println("before $i")
           error()
           println("after $i")
       end
before 1before 1before 1before 7before 4


signal (11): Segmentation fault: 11
while loading no file, in expression starting on line 0
uv__write at /Users/rene/local/julia5/deps/srccache/libuv-8d5131b6c1595920dd30644cd1435b4f344b46c8/src/unix/stream.c:890
uv_write2 at /Users/rene/local/julia5/deps/srccache/libuv-8d5131b6c1595920dd30644cd1435b4f344b46c8/src/unix/stream.c:1450
uv_write at /Users/rene/local/julia5/deps/srccache/libuv-8d5131b6c1595920dd30644cd1435b4f344b46c8/src/unix/stream.c:1475
jl_uv_write at /Users/rene/local/julia5/src/jl_uv.c:424
uv_write at ./stream.jl:809
unsafe_write at ./stream.jl:830
write at ./io.jl:175

Note that before 1 gets printed several times.

[yuyichao]

Dup of #17532 and #17388