Fix some JET errors around matching methods for `send_connection_hdr(...)` and `send_msg_now(...)` (underlying problem: the `Worker(...)` constructors might not always return a `Worker`) by DilumAluthge · Pull Request #180 · JuliaLang/Distributed.jl

DilumAluthge · 2026-02-20T14:44:01Z

Cherry-picked out of #164

┌ create_worker(manager::Distributed.ClusterManager, wconfig::Distributed.WorkerConfig) @ Distributed ~/Distributed.jl/src/cluster.jl:709
│ no matching method found `send_connection_hdr(::Distributed.LocalProcess, ::Bool)` (1/2 union split): Distributed.send_connection_hdr(w::Union{Distributed.LocalProcess, Distributed.Worker}, true)
└────────────────────

┌ create_worker(manager::Distributed.ClusterManager, wconfig::Distributed.WorkerConfig) @ Distributed ~/Distributed.jl/src/cluster.jl:712
│ no matching method found `send_msg_now(::Distributed.LocalProcess, ::Distributed.MsgHeader, ::Distributed.JoinPGRPMsg)` (1/2 union split): Distributed.send_msg_now(w::Union{Distributed.LocalProcess, Distributed.Worker}, Distributed.MsgHeader(Distributed.RRID(0, 0)::Distributed.RRID, ntfy_oid::Distributed.RRID)::Distributed.MsgHeader, join_message)
└────────────────────

The underlying problem seems to be that the Worker(...) constructors might not always return a Worker. See also: #182

codecov · 2026-02-20T14:52:51Z

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 79.47%. Comparing base (231da28) to head (5cf8ca4).
⚠️ Report is 1 commits behind head on master.

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@@           Coverage Diff           @@
##           master     #180   +/-   ##
=======================================
  Coverage   79.47%   79.47%           
=======================================
  Files          10       10           
  Lines        1959     1959           
=======================================
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  Misses        402      402

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JamesWrigley · 2026-02-20T22:41:37Z

src/cluster.jl

    end

-    w = Worker(w_stub.id, r_s, w_s, manager; config=wconfig)
+    w = Worker(w_stub.id, r_s, w_s, manager; config=wconfig)::Worker


Would this also be fixed by adding ::Worker return annotations to the constructors?

Hmmm. I think we need to look at this code closer.

The problematic line seems to be line 143 here:

Distributed.jl/src/cluster.jl

Lines 140 to 152 in d06aa73

function Worker(id::Int, conn_func)

@assert id > 0

if haskey(map_pid_wrkr, id)

return map_pid_wrkr[id]

end

w=new(id, Threads.ReentrantLock(), [], [], false, W_CREATED, Threads.Condition(), time(), conn_func)

w.initialized = Event()

register_worker(w)

w

end

Worker() = Worker(get_next_pid())

end

Line 143 is this line:

return map_pid_wrkr[id]

map_pid_wrkr is a global constant. The problem (I think) is the type of map_pid_wrkr:

Distributed.jl/src/cluster.jl

Line 850 in d06aa73

const map_pid_wrkr = Dict{Int, Union{Worker, LocalProcess}}()

So when we index into map_pid_wrkr with map_pid_wrkr[id], how do we know whether map_pid_wrkr[id] is a Worker or a LocalProcess?

Wow, I absolutely hate that 🤮 But something to fix another time... We could safely add an annotation to this constructor though, which I think is the one getting called here:

Distributed.jl/src/cluster.jl

Line 124 in d06aa73

function Worker(id::Int, r_stream::IO, w_stream::IO, manager::ClusterManager;

I tried adding ::Worker to that constructor (the constructor starting on line 124), but that's not sufficient. Here's the source code for that constructor:

Distributed.jl/src/cluster.jl

Lines 124 to 137 in 2adcd26

function Worker(id::Int, r_stream::IO, w_stream::IO, manager::ClusterManager;

version::Union{VersionNumber, Nothing}=nothing,

config::WorkerConfig=WorkerConfig())

w = Worker(id)

w.r_stream = r_stream

w.w_stream = buffer_writes(w_stream)

w.w_serializer = ClusterSerializer(w.w_stream)

w.manager = manager

w.config = config

w.version = version

set_worker_state(w, W_CONNECTED)

register_worker_streams(w)

w

end

The problem is, on line 127, that constructor calls the Worker(::Int) constructor, which in turn calls the Worker(::Int, ::Any) constructor, and now we're in the Worker(::Int, ::Any) constructor, which is the constructor that includes the return map_pid_wrkr[id] line.

So, if I try adding ::Worker to the line 124 constructor, JET still complains, because Worker(::Int, ::Any) might return a LocalProcess.

Bleh, devastating.

I've opened an issue: #182

…...)` and `send_msg_now(...)` ``` ┌ create_worker(manager::Distributed.ClusterManager, wconfig::Distributed.WorkerConfig) @ Distributed ~/Distributed.jl/src/cluster.jl:709 │ no matching method found `send_connection_hdr(::Distributed.LocalProcess, ::Bool)` (1/2 union split): Distributed.send_connection_hdr(w::Union{Distributed.LocalProcess, Distributed.Worker}, true) └──────────────────── ``` ``` ┌ create_worker(manager::Distributed.ClusterManager, wconfig::Distributed.WorkerConfig) @ Distributed ~/Distributed.jl/src/cluster.jl:712 │ no matching method found `send_msg_now(::Distributed.LocalProcess, ::Distributed.MsgHeader, ::Distributed.JoinPGRPMsg)` (1/2 union split): Distributed.send_msg_now(w::Union{Distributed.LocalProcess, Distributed.Worker}, Distributed.MsgHeader(Distributed.RRID(0, 0)::Distributed.RRID, ntfy_oid::Distributed.RRID)::Distributed.MsgHeader, join_message) └──────────────────── ``` (cherry picked from commit 3e74cbc)

JamesWrigley

LGTM! (with sadness)

JamesWrigley reviewed Feb 20, 2026

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DilumAluthge force-pushed the dpa/fix-jet-send_connection_hdr branch from 1eaff36 to a18f0b9 Compare February 21, 2026 08:03

Merge branch 'master' into dpa/fix-jet-send_connection_hdr

5cf8ca4

JamesWrigley approved these changes Feb 21, 2026

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DilumAluthge mentioned this pull request Feb 21, 2026

Worker(...) constructors might not always return an object of type Worker? #182

Open

DilumAluthge marked this pull request as ready for review February 21, 2026 08:41

DilumAluthge merged commit d396a8c into master Feb 21, 2026
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DilumAluthge deleted the dpa/fix-jet-send_connection_hdr branch February 21, 2026 08:50

DilumAluthge mentioned this pull request Feb 22, 2026

Forwardports from Distributed.jl#master JuliaParallel/DistributedNext.jl#49

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Fix some JET errors around matching methods for `send_connection_hdr(...)` and `send_msg_now(...)` (underlying problem: the `Worker(...)` constructors might not always return a `Worker`)#180

Fix some JET errors around matching methods for `send_connection_hdr(...)` and `send_msg_now(...)` (underlying problem: the `Worker(...)` constructors might not always return a `Worker`)#180
DilumAluthge merged 2 commits intomasterfrom
dpa/fix-jet-send_connection_hdr

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	function Worker(id::Int, conn_func)
	@assert id > 0
	if haskey(map_pid_wrkr, id)
	return map_pid_wrkr[id]
	end
	w=new(id, Threads.ReentrantLock(), [], [], false, W_CREATED, Threads.Condition(), time(), conn_func)
	w.initialized = Event()
	register_worker(w)
	w
	end

	Worker() = Worker(get_next_pid())
	end

	function Worker(id::Int, r_stream::IO, w_stream::IO, manager::ClusterManager;
	version::Union{VersionNumber, Nothing}=nothing,
	config::WorkerConfig=WorkerConfig())
	w = Worker(id)
	w.r_stream = r_stream
	w.w_stream = buffer_writes(w_stream)
	w.w_serializer = ClusterSerializer(w.w_stream)
	w.manager = manager
	w.config = config
	w.version = version
	set_worker_state(w, W_CONNECTED)
	register_worker_streams(w)
	w
	end

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