From d6babb981749c20b0506d31906269da3f54b6379 Mon Sep 17 00:00:00 2001
From: Dilum Aluthge <dilum@aluthge.com>
Date: Fri, 20 Feb 2026 08:18:19 -0500
Subject: [PATCH] Change `Distributed.cluster_manager` from a global
 non-constant `ClusterManager` to a global constant `Ref{ClusterManager}`
 (#177)

This is a forward-port of https://github.com/JuliaLang/Distributed.jl/pull/177 (https://github.com/JuliaLang/Distributed.jl/commit/2fe1aa4e267517565e99cd06664550dcd230cfc6).

(cherry picked from commit 2fe1aa4e267517565e99cd06664550dcd230cfc6)
---
 src/cluster.jl          | 11 +++++++++--
 src/process_messages.jl |  8 ++++++--
 2 files changed, 15 insertions(+), 4 deletions(-)

diff --git a/src/cluster.jl b/src/cluster.jl
index 2c8f2f7..50e4627 100644
--- a/src/cluster.jl
+++ b/src/cluster.jl
@@ -9,6 +9,14 @@ Cluster managers implement how workers can be added, removed and communicated wi
 """
 abstract type ClusterManager end
 
+# cluster_manager is a global constant
+const cluster_manager = Ref{ClusterManager}()
+
+function throw_if_cluster_manager_unassigned()
+    isassigned(cluster_manager) || error("cluster_manager is unassigned")
+    return nothing
+end
+
 """
     WorkerConfig
 
@@ -390,8 +398,7 @@ function init_worker(cookie::AbstractString, manager::ClusterManager=DefaultClus
 
     # On workers, the default cluster manager connects via TCP sockets. Custom
     # transports will need to call this function with their own manager.
-    global cluster_manager
-    cluster_manager = manager
+    cluster_manager[] = manager
 
     # Since our pid has yet to be set, ensure no RemoteChannel / Future  have been created or addprocs() called.
     @assert nprocs() <= 1
diff --git a/src/process_messages.jl b/src/process_messages.jl
index a444651..33d6fe3 100644
--- a/src/process_messages.jl
+++ b/src/process_messages.jl
@@ -315,6 +315,8 @@ function handle_msg(msg::ResultMsg, header, r_stream, w_stream, version)
 end
 
 function handle_msg(msg::IdentifySocketMsg, header, r_stream, w_stream, version)
+    throw_if_cluster_manager_unassigned()
+
     # register a new peer worker connection
     w = Worker(msg.from_pid, r_stream, w_stream, cluster_manager; version=version)
     send_connection_hdr(w, false)
@@ -328,6 +330,8 @@ function handle_msg(msg::IdentifySocketAckMsg, header, r_stream, w_stream, versi
 end
 
 function handle_msg(msg::JoinPGRPMsg, header, r_stream, w_stream, version)
+    throw_if_cluster_manager_unassigned()
+
     LPROC.id = msg.self_pid
     controller = Worker(1, r_stream, w_stream, cluster_manager; version=version)
     notify(controller.initialized)
@@ -348,9 +352,9 @@ function handle_msg(msg::JoinPGRPMsg, header, r_stream, w_stream, version)
         let rpid=rpid, wconfig=wconfig
             if lazy
                 # The constructor registers the object with a global registry.
-                Worker(rpid, ()->connect_to_peer(cluster_manager, rpid, wconfig))
+                Worker(rpid, ()->connect_to_peer(cluster_manager[], rpid, wconfig))
             else
-                @async connect_to_peer(cluster_manager, rpid, wconfig)
+                @async connect_to_peer(cluster_manager[], rpid, wconfig)
             end
         end
     end