Missing `println` output with `wait(::Event); println("done")`

General Usage
1

Hi all :slight_smile:

Can you check if the done2 is also missing for you?
Here is my code:

julia> e = Base.Event()
Base.Event(Base.GenericCondition{ReentrantLock}(Base.IntrusiveLinkedList{Task}(nothing, nothing), ReentrantLock(nothing, 0x00000000, 0x00, Base.GenericCondition{Base.Threads.SpinLock}(Base.IntrusiveLinkedList{Task}(nothing, nothing), Base.Threads.SpinLock(0)), (8, 0, -1))), false, false)

julia> [Threads.@spawn begin wait(e); println("done$i") end for i in 1:10]
10-element Vector{Task}:
 Task (runnable, started) @0x0000014db88ea6d0
 Task (runnable, started) @0x0000014db88ea8c0
 Task (runnable, started) @0x0000014db88eaab0
 Task (runnable, started) @0x0000014db88eaca0
 Task (runnable, started) @0x0000014db88eae90
 Task (runnable, started) @0x0000014db88eb080
 Task (runnable, started) @0x0000014db88eb270
 Task (runnable, started) @0x0000014db88eb460
 Task (runnable, started) @0x0000014db88eb650
 Task (runnable, started) @0x0000014db88eb840

julia> notify(e)
done1
# missing done2
julia>
done3
done4
done5
done6
done7
done8
done9
done10

Should we fix it? Is it only a repl problem?

Cheers

2

I’m guessing the REPL prompt is competing with done2 for printing to the terminal.

3

Is printing not thread safe?

4

Note that you can ‘solve’ the problem in the REPL by adding a sleep after the notify, in order to give enough time to print to stdio, confirming @BioTurboNick 's hypothesis.

No sleep 
julia> e = Base.Event();

julia> [Threads.@spawn begin wait(e); println("done$i") end for i in 1:10]
10-element Vector{Task}:
 Task (runnable) @0x0000015fc48f64e0
 Task (runnable) @0x0000015fc48f66d0
 Task (runnable) @0x0000015fc48f68c0
 Task (runnable) @0x0000015fc48f6ab0
 Task (runnable) @0x0000015fc48f6ca0
 Task (runnable) @0x0000015fc48f6e90
 Task (runnable) @0x0000015fc48f7080
 Task (runnable) @0x0000015fc48f7270
 Task (runnable) @0x0000015fc48f7460
 Task (runnable) @0x0000015fc48f7650

julia> notify(e)
done7

julia> done9
julia> done8
done1
done2
done3
done10
done4
done6
done5
With sleep 
julia> e = Base.Event();

julia> [Threads.@spawn begin wait(e); println("done$i") end for i in 1:10]
10-element Vector{Task}:
 Task (runnable) @0x0000015fc48f7840
 Task (runnable) @0x0000015fc48f7a30
 Task (runnable) @0x0000015fc48f7c20
 Task (runnable) @0x0000015fc48f7e10
 Task (runnable) @0x0000015f9ba5c010
 Task (runnable) @0x0000015f9ba5c200
 Task (runnable) @0x0000015f9ba5c3f0
 Task (runnable) @0x0000015f9ba5c5e0
 Task (runnable) @0x0000015f9ba5c7d0
 Task (runnable) @0x0000015f9ba5c9c0

julia> notify(e); sleep(0.1)
done3
done5
done4
done9
done7
done1
done6
done8
done2
done10