Make Distributed.Worker threadsafe (#38134)

Co-authored-by: Jonas Schulze <jonas.schulze@st.ovgu.de>

stdlib/Distributed/src/cluster.jl

@@ -99,7 +99,7 @@ mutable struct Worker
     add_msgs::Array{Any,1}
     gcflag::Bool
     state::WorkerState
-    c_state::Condition      # wait for state changes
+    c_state::Event          # wait for state changes
     ct_time::Float64        # creation time
     conn_func::Any          # used to setup connections lazily
 
@@ -133,7 +133,7 @@ mutable struct Worker
         if haskey(map_pid_wrkr, id)
             return map_pid_wrkr[id]
         end
-        w=new(id, [], [], false, W_CREATED, Condition(), time(), conn_func)
+        w=new(id, [], [], false, W_CREATED, Event(), time(), conn_func)
         w.initialized = Event()
         register_worker(w)
         w
@@ -144,7 +144,7 @@ end
 
 function set_worker_state(w, state)
     w.state = state
-    notify(w.c_state; all=true)
+    notify(w.c_state)
 end
 
 function check_worker_state(w::Worker)
@@ -189,7 +189,7 @@ function wait_for_conn(w)
         timeout =  worker_timeout() - (time() - w.ct_time)
         timeout <= 0 && error("peer $(w.id) has not connected to $(myid())")
 
-        @async (sleep(timeout); notify(w.c_state; all=true))
+        @async (sleep(timeout); notify(w.c_state))
         wait(w.c_state)
         w.state === W_CREATED && error("peer $(w.id) didn't connect to $(myid()) within $timeout seconds")
     end

stdlib/Distributed/test/distributed_exec.jl

@@ -1711,4 +1711,5 @@ include("splitrange.jl")
 # Run topology tests last after removing all workers, since a given
 # cluster at any time only supports a single topology.
 rmprocs(workers())
+include("threads.jl")
 include("topology.jl")

stdlib/Distributed/test/threads.jl

@@ -0,0 +1,61 @@
+using Test
+using Distributed, Base.Threads
+using Base.Iterators: product
+
+exeflags = ("--startup-file=no",
+            "--check-bounds=yes",
+            "--depwarn=error",
+            "--threads=2")
+
+function call_on(f, wid, tid)
+  remotecall(wid) do
+    t = Task(f)
+    ccall(:jl_set_task_tid, Cvoid, (Any, Cint), t, tid-1)
+    schedule(t)
+    @assert threadid(t) == tid
+    t
+  end
+end
+
+# Run function on process holding the data to only serialize the result of f.
+# This becomes useful for things that cannot be serialized (e.g. running tasks)
+# or that would be unnecessarily big if serialized.
+fetch_from_owner(f, rr) = remotecall_fetch(f∘fetch, rr.where, rr)
+
+isdone(rr) = fetch_from_owner(istaskdone, rr)
+isfailed(rr) = fetch_from_owner(istaskfailed, rr)
+
+@testset "RemoteChannel allows put!/take! from thread other than 1" begin
+  ws = ts = product(1:2, 1:2)
+  @testset "from worker $w1 to $w2 via 1" for (w1, w2) in ws
+    @testset "from thread $w1.$t1 to $w2.$t2" for (t1, t2) in ts
+      # We want (the default) lazyness, so that we wait for `Worker.c_state`!
+      procs_added = addprocs(2; exeflags, lazy=true)
+      @everywhere procs_added using Base.Threads
+      p1 = procs_added[w1]
+      p2 = procs_added[w2]
+      chan_id = first(procs_added)
+      chan = RemoteChannel(chan_id)
+      send = call_on(p1, t1) do
+        put!(chan, nothing)
+      end
+      recv = call_on(p2, t2) do
+        take!(chan)
+      end
+
+      # Wait on the spawned tasks on the owner
+      @sync begin
+        @async fetch_from_owner(wait, recv)
+        @async fetch_from_owner(wait, send)
+      end
+
+      # Check the tasks
+      @test isdone(send)
+      @test isdone(recv)
+
+      @test !isfailed(send)
+      @test !isfailed(recv)
+      rmprocs(procs_added)
+    end
+  end
+end