use interactive threadpool if possible

Author: IanButterworth

base/client.jl

@@ -540,7 +540,7 @@ function _start()
         elseif (repl_was_requested || is_interactive)
             # Run the Base `main`, which will either load the REPL stdlib
             # or run the fallback REPL
-            ret = fetch(Threads.@spawn repl_main(ARGS))
+            ret = fetch(Threads.@spawn :interactive repl_main(ARGS))
         end
         ret === nothing && (ret = 0)
         ret = Cint(ret)

stdlib/REPL/src/LineEdit.jl

@@ -198,7 +198,7 @@ function beep(s::PromptState, duration::Real=options(s).beep_duration,
     isinteractive() || return # some tests fail on some platforms
     s.beeping = min(s.beeping + duration, maxduration)
     let colors = Base.copymutable(colors)
-        errormonitor(Threads.@spawn begin
+        errormonitor(Threads.@spawn :interactive begin
             trylock(s.refresh_lock) || return
             try
                 orig_prefix = s.p.prompt_prefix
@@ -2829,7 +2829,7 @@ function prompt!(term::TextTerminal, prompt::ModalInterface, s::MIState = init_s
         activate(prompt, s, term, term)
         old_state = mode(s)
         l = Base.ReentrantLock()
-        t = Threads.@spawn while true
+        t = Threads.@spawn :interactive while true
             wait(s.async_channel)
             status = @lock l begin
                 fcn = take!(s.async_channel)

stdlib/REPL/src/REPL.jl

@@ -327,15 +327,15 @@ function start_repl_backend(repl_channel::Channel{Any}, response_channel::Channe
     # Maintain legacy behavior of asynchronous backend
     backend = REPLBackend(repl_channel, response_channel, false)
     # Assignment will be made twice, but will be immediately available
-    backend.backend_task = Threads.@spawn start_repl_backend(backend; get_module)
+    backend.backend_task = Threads.@spawn :interactive start_repl_backend(backend; get_module)
     return backend
 end
 
 """
     start_repl_backend(backend::REPLBackend)
 
     Call directly to run backend loop on current Task.
-    Use Threads.@spawn for run backend on new Task.
+    Use Threads.@spawn :interactive for run backend on new Task.
 
     Does not return backend until loop is finished.
 """
@@ -495,12 +495,12 @@ function run_repl(repl::AbstractREPL, @nospecialize(consumer = x -> nothing); ba
         end
     get_module = () -> active_module(repl)
     if backend_on_current_task
-        t = Threads.@spawn run_frontend(repl, backend_ref)
+        t = Threads.@spawn :interactive run_frontend(repl, backend_ref)
         errormonitor(t)
         Base._wait2(t, cleanup)
         start_repl_backend(backend, consumer; get_module)
     else
-        t = Threads.@spawn start_repl_backend(backend, consumer; get_module)
+        t = Threads.@spawn :interactive start_repl_backend(backend, consumer; get_module)
         errormonitor(t)
         Base._wait2(t, cleanup)
         run_frontend(repl, backend_ref)
@@ -1266,7 +1266,7 @@ function setup_interface(
                 end
                 # load Pkg on another thread if available so that typing in the dummy Pkg prompt
                 # isn't blocked, but instruct the main REPL task to do the transition via s.async_channel
-                t_replswitch = Threads.@spawn begin
+                t_replswitch = Threads.@spawn :default begin
                     REPLExt = load_pkg()
                     if REPLExt isa Module && isdefined(REPLExt, :PkgCompletionProvider)
                         put!(s.async_channel,