do not lock up addproc on worker setup timeout

This is a corollary to the previous commit in JuliaLang#32290, and implements suggestions thereof.

It restricts the master to wait for a worker to respond within `Distributed.worker_timeout()` seconds. Beyond that it releases the lock on `rr_ntfy_join` with a special flag `:TIMEDOUT`. This flag is set to `:ERROR` in case of any errors during worker setup, and to `:OK` when the master received a `JoinCompleteMsg` indicating setup completion from worker.

`addprocs` returns the worker id in the list of workers it added only if it has received a `JoinCompleteMsg`, that is, only when `rr_ntfy_join` contains `:OK`. Note that the worker process may not be dead yet, and it may still be listed in `workers()` until it actually goes down.

stdlib/Distributed/src/cluster.jl

@@ -527,8 +527,14 @@ function create_worker(manager, wconfig)
     # Start a new task to handle inbound messages from connected worker in master.
     # Also calls `wait_connected` on TCP streams.
     procmsg_task = process_messages(w.r_stream, w.w_stream, false)
+    timeout = worker_timeout()
     Timer(1, interval=1) do timer
-        istaskstarted(procmsg_task) && istaskdone(procmsg_task) && put!(rr_ntfy_join, nothing)
+        timeout -= 1
+        if timeout <= 0.0
+            put!(rr_ntfy_join, :TIMEDOUT)
+        elseif istaskdone(procmsg_task)
+            put!(rr_ntfy_join, :ERROR)
+        end
         isready(rr_ntfy_join) && close(timer)
     end
 
@@ -591,7 +597,7 @@ function create_worker(manager, wconfig)
         delete!(PGRP.refs, ntfy_oid)
     end
 
-    return istaskdone(procmsg_task) ? 0 : w.id
+    return (fetch(rr_ntfy_join.c) === :OK) ? w.id : 0
 end
 
 

stdlib/Distributed/src/process_messages.jl

@@ -355,7 +355,7 @@ function handle_msg(msg::JoinCompleteMsg, header, r_stream, w_stream, version)
     w.version = version
 
     ntfy_channel = lookup_ref(header.notify_oid)
-    put!(ntfy_channel, w.id)
+    put!(ntfy_channel, :OK)
 
     push!(default_worker_pool(), w.id)
 end

stdlib/Distributed/test/distributed_exec.jl

@@ -1521,14 +1521,25 @@ try
     npids = addprocs(1; topology=:all_to_all, lazy=false)
     @test length(npids) == 1
     @test nprocs() == 2
+    w2_connect_at = Distributed.PGRP.workers[2].config.connect_at
+
+    # test condition where connect fails immediately
     lsock = listenany(ip"127.0.0.1", 20000)
-    Distributed.PGRP.workers[2].config.connect_at=("127.0.0.1", lsock[1])
+    Distributed.PGRP.workers[2].config.connect_at = ("127.0.0.1", lsock[1])
     close(lsock[2])
     npids = addprocs_with_testenv(1; topology=:all_to_all, lazy=false)
     @test length(npids) == 0
     @test nprocs() == 2
-    (nprocs() > 1) && rmprocs(workers())
+
+    # test condition where connect times out
+    # using a non routable IP to test, ref: https://tools.ietf.org/html/rfc5737
+    Distributed.PGRP.workers[2].config.connect_at = ("203.0.113.0", w2_connect_at[2])
+    withenv("JULIA_WORKER_TIMEOUT"=>1) do
+        npids = addprocs_with_testenv(1; topology=:all_to_all, lazy=false)
+        @test length(npids) == 0
+    end
 finally
+    rmprocs(workers())
     redirect_stderr(old_stderr)
     close(stderr_in)
 end