Replace the stdlib watcher task with a Timer

This needs to be shutdown cleanly or the lingering watcher task can cause
hangs.

Author: JamesWrigley

docs/src/_changelog.md

@@ -7,6 +7,12 @@ CurrentModule = DistributedNext
 This documents notable changes in DistributedNext.jl. The format is based on
 [Keep a Changelog](https://keepachangelog.com).
 
+## Unreleased
+
+### Fixed
+- Backported various fixes from Distributed ([#25]).
+- Fixed a lingering task that could cause hangs when exiting Distributed ([#51]).
+
 ## [v1.1.0] - 2025-08-02
 
 ### Fixed

src/DistributedNext.jl

@@ -132,7 +132,10 @@ include("pmap.jl")
 include("managers.jl")    # LocalManager and SSHManager
 include("precompile.jl")
 
+_stdlib_watcher_timer::Union{Timer, Nothing} = nothing
+
 function __init__()
+    global _stdlib_watcher_timer
     init_parallel()
 
     if ccall(:jl_generating_output, Cint, ()) == 0
@@ -141,20 +144,12 @@ function __init__()
         # cluster cookie has been set, which is most likely to have been done
         # through Distributed.init_multi() being called by Distributed.addprocs() or
         # something.
-        watcher_task = Threads.@spawn while true
+        _stdlib_watcher_timer = Timer(0; interval=1) do timer
             if _check_distributed_active()
-                return
-            end
-
-            try
-                sleep(1)
-            catch
-                # sleep() may throw when the internal object it waits on is closed
-                # as the process exits.
-                return
+                close(timer)
             end
         end
-        errormonitor(watcher_task)
+        atexit(() -> close(_stdlib_watcher_timer))
     end
 end