REPL errors "randomly" after fake Pkg prompt PR

[KristofferC]

Just as an example:

(Base) julia> Base.explicit_loadUnhandled Task ERROR: TaskFailedException

    nested task error: ArgumentError: IOBuffer not marked
    Stacktrace:
     [1] reset
       @ ./io.jl:1429 [inlined]
     [2] reset
       @ ./stream.jl:1489 [inlined]
     [3] peek(s::TTY, ::Type{Char})
       @ Base ./stream.jl:1496
     [4] peek(t::REPL.Terminals.TTYTerminal, ::Type{Char})
       @ REPL.Terminals ~/julia/usr/share/julia/stdlib/v1.12/REPL/src/Terminals.jl:161
     [5] (::REPL.LineEdit.var"#281#283"{REPL.Terminals.TTYTerminal})()
       @ REPL.LineEdit ~/julia/usr/share/julia/stdlib/v1.12/REPL/src/LineEdit.jl:2834
Stacktrace:
 [1] _wait_multiple(waiting_tasks::Tuple{Task, Task}, throwexc::Bool, all::Bool, failfast::Bool)
   @ Base ./task.jl:513
 [2] _wait_multiple
   @ ./task.jl:417 [inlined]
 [3] waitany
   @ ./task.jl:397 [inlined]
 [4] prompt!(term::REPL.Terminals.TextTerminal, prompt::REPL.LineEdit.ModalInterface, s::REPL.LineEdit.MIState)
   @ REPL.LineEdit ~/julia/usr/share/julia/stdlib/v1.12/REPL/src/LineEdit.jl:2833
 [5] run_interface(terminal::REPL.Terminals.TextTerminal, m::REPL.LineEdit.ModalInterface, s::REPL.LineEdit.MIState)
   @ REPL.LineEdit ~/julia/usr/share/julia/stdlib/v1.12/REPL/src/LineEdit.jl:2743
 [6] run_frontend(repl::REPL.LineEditREPL, backend::REPL.REPLBackendRef)
   @ REPL ~/julia/usr/share/julia/stdlib/v1.12/REPL/src/REPL.jl:1504
 [7] (::REPL.var"#75#81"{REPL.LineEditREPL, REPL.REPLBackendRef})()
   @ REPL ~/julia/usr/share/julia/stdlib/v1.12/REPL/src/REPL.jl:496
ERROR: TaskFailedException
Stacktrace:
  [1] try_yieldto(undo::typeof(ensure_rescheduled))
    @ Base ./task.jl:1100
  [2] wait()
    @ Base ./task.jl:1164
  [3] wait(c::GenericCondition{ReentrantLock}; first::Bool)
    @ Base ./condition.jl:139
  [4] wait
    @ ./condition.jl:134 [inlined]
  [5] take_buffered(c::Channel{Any})
    @ Base ./channels.jl:493
  [6] take!
    @ ./channels.jl:487 [inlined]
  [7] repl_backend_loop(backend::REPL.REPLBackend, get_module::Function)
    @ REPL ~/julia/usr/share/julia/stdlib/v1.12/REPL/src/REPL.jl:353
  [8] start_repl_backend(backend::REPL.REPLBackend, consumer::Any; get_module::Function)
    @ REPL ~/julia/usr/share/julia/stdlib/v1.12/REPL/src/REPL.jl:343
  [9] run_repl(repl::REPL.AbstractREPL, consumer::Any; backend_on_current_

Probably related to #54674 looking at the blame.

cc @IanButterworth

[IanButterworth]

Seems to be an issue with this line. Is there a more correct way to wait on input but not error on eof?

julia/stdlib/REPL/src/LineEdit.jl

Line 2834 in ce38f08

@async(eof(term) || peek(term, Char)),

[vtjnash]

Normally, the way to do that is to have 2 separate tasks, each responsible for one event, instead of having 3 tasks, each responsible for a semi-arbitrary set of events

[IanButterworth]

Sorry, I don't understand. Would you mind elaborating with code?

[vtjnash]

Split each thing you want to do into a separate task, and don't try to complicatedly intermix them by ever using waitany

[IanButterworth]

I want to wait for the first of either

• new input being available from stdin, but not consume it, because it's consumed inside match_input
• a new function that needs executing from s.async_channel

The current design is the only way I know how to do that without blocking while waiting on stdin or throwing away new input on stdin

[vtjnash]

I think there are already a few other clients similar to that (e.g. see beep), though the current implementation of MVC does seem probably too tightly coupled between input and output to allow the clean injection of events that are not from the keymap

[vtjnash]

Reading from stdin without consuming the input introduces a data race into the design, which is probably why it crashes for some people periodically