# Can't remove process when added on different thread

**URL:** <https://discourse.julialang.org/t/cant-remove-process-when-added-on-different-thread/129357>\
**Category:** General Usage\
**Tags:** multithreading, error, distributed\
**Created:** [May 26, 2025, 6:16pm UTC](https://discourse.julialang.org/t/cant-remove-process-when-added-on-different-thread/129357 "2025-05-26T18:16:30Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![NonDairyNeutrino](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/nondairyneutrino/32/221496_2.png) [@NonDairyNeutrino](https://discourse.julialang.org/u/NonDairyNeutrino)\
**Post date:** [May 26, 2025, 6:16pm UTC](https://discourse.julialang.org/t/cant-remove-process-when-added-on-different-thread/129357/1 "2025-05-26T18:16:30Z")

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It seems that when a worker process is added on a thread with threadid != 1 (probably), it can’t be naively removed. For example

```julia
using Distributed

new_proc = fetch(Threads.@spawn addprocs(1)) |> only
rmprocs(new_proc)

```

results in

```julia
ERROR: ConcurrencyViolationError("lock must be held")
Stacktrace:
  [1] concurrency_violation()
    @ Base ./condition.jl:8
  [2] assert_havelock
    @ ./condition.jl:25 [inlined]
  [3] assert_havelock
    @ ./condition.jl:48 [inlined]
  [4] assert_havelock
    @ ./condition.jl:72 [inlined]
  [5] notify(c::Condition, arg::Any, all::Bool, error::Bool)
    @ Base ./condition.jl:150
  [6] notify (repeats 2 times)
    @ ./condition.jl:148 [inlined]
  [7] set_worker_state
    @ ~/.julia/juliaup/julia-1.11.5+0.x64.linux.gnu/share/julia/stdlib/v1.11/Distributed/src/cluster.jl:148 [inlined]
  [8] _rmprocs(pids::Vector{Int64}, waitfor::Int64)
    @ Distributed ~/.julia/juliaup/julia-1.11.5+0.x64.linux.gnu/share/julia/stdlib/v1.11/Distributed/src/cluster.jl:1053
  [9] rmprocs(pids::Int64; waitfor::Int64)
    @ Distributed ~/.julia/juliaup/julia-1.11.5+0.x64.linux.gnu/share/julia/stdlib/v1.11/Distributed/src/cluster.jl:1037
 [10] rmprocs(pids::Int64)
    @ Distributed ~/.julia/juliaup/julia-1.11.5+0.x64.linux.gnu/share/julia/stdlib/v1.11/Distributed/src/cluster.jl:1028
 [11] top-level scope
    @ REPL[7]:1

```

This isn’t even a question of “adding multiple processes in parallel” (though that’s where it started), but rather why does _seem_ like the threadid affects the removal but not the creation? It makes sense there would be a lock on each worker, but is that lock bound to the thread on which it was created?

---

<div class="post-metadata">

**Author:** ![JamesNZ](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/jamesnz/32/35361_2.png) [@JamesNZ](https://discourse.julialang.org/u/JamesNZ)\
**Post date:** [May 26, 2025, 9:02pm UTC](https://discourse.julialang.org/t/cant-remove-process-when-added-on-different-thread/129357/2 "2025-05-26T21:02:44Z")

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Unfortunately Distributed was never threadsafe 🙃 That has been fixed in Julia 1.12, and indeed your MWE works for me in the 1.12 beta.

---

<div class="post-metadata">

**Author:** ![NonDairyNeutrino](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/nondairyneutrino/32/221496_2.png) [@NonDairyNeutrino](https://discourse.julialang.org/u/NonDairyNeutrino)\
**Post date:** [May 26, 2025, 9:05pm UTC](https://discourse.julialang.org/t/cant-remove-process-when-added-on-different-thread/129357/3 "2025-05-26T21:05:05Z")

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Huh, TIL. 1.12 is gonna be sick!