# \`KeyError\` when using \`pmap\`

**URL:** <https://discourse.julialang.org/t/keyerror-when-using-pmap/114464>\
**Category:** General Usage\
**Tags:** question, package, distributed, parallel-computing\
**Created:** [May 20, 2024, 3:26am UTC](https://discourse.julialang.org/t/keyerror-when-using-pmap/114464 "2024-05-20T03:26:11Z")\
**Posts on this page:** 4\
**Page:** 1

<div class="post-metadata">

**Author:** ![WuSiren](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/wusiren/32/42529_2.png) [@WuSiren](https://discourse.julialang.org/u/WuSiren)\
**Post date:** [May 20, 2024, 3:26am UTC](https://discourse.julialang.org/t/keyerror-when-using-pmap/114464/1 "2024-05-20T03:26:11Z")

</div>

I’m trying to use `pmap` form `Distributed.jl` for parallel computing in the `runtests.jl` file of a package (`MyPkg`) that is in development. The code is like:

```julia
# runtests.jl

using Distributed: @everywhere, addprocs, pmap
using MyPkg

myvect = [...] # The vector that is to be computed by `myfunc` parallelly.

addprocs(2)
@time result = pmap(myfunc, myvect); # `myfunc` is defined in `MyPkg.jl` (and other `.jl` files included by it)

```

If the last line is `map(myfunc, myvect)` the code can run normally. But when I change it to `map(myfunc, myvect)`, it repots:

```julia
ERROR: On worker 2:
KeyError: key MyPkg[8f2d0ece-bb0f-4d0c-a9d4-8a8c66038d81] not found
Stacktrace:
  [1] getindex
    @ .\dict.jl:498 [inlined]
  [2] macro expansion
    @ .\lock.jl:267 [inlined]
  [3] root_module
    @ .\loading.jl:1878
  [4] deserialize_module
    @ D:\Software\julia-1.10.3\share\julia\stdlib\v1.10\Serialization\src\Serialization.jl:994
  [5] handle_deserialize
    @ D:\Software\julia-1.10.3\share\julia\stdlib\v1.10\Serialization\src\Serialization.jl:896
  [6] deserialize
    @ D:\Software\julia-1.10.3\share\julia\stdlib\v1.10\Serialization\src\Serialization.jl:814
  [7] deserialize_datatype
    @ D:\Software\julia-1.10.3\share\julia\stdlib\v1.10\Serialization\src\Serialization.jl:1398
  [8] handle_deserialize
    @ D:\Software\julia-1.10.3\share\julia\stdlib\v1.10\Serialization\src\Serialization.jl:867
  [9] deserialize
    @ D:\Software\julia-1.10.3\share\julia\stdlib\v1.10\Serialization\src\Serialization.jl:814
 [10] handle_deserialize
    @ D:\Software\julia-1.10.3\share\julia\stdlib\v1.10\Serialization\src\Serialization.jl:874
 [11] deserialize
    @ D:\Software\julia-1.10.3\share\julia\stdlib\v1.10\Serialization\src\Serialization.jl:814 [inlined]
 [12] deserialize_global_from_main
    @ D:\Software\julia-1.10.3\share\julia\stdlib\v1.10\Distributed\src\clusterserialize.jl:160
 [13] #5
    @ D:\Software\julia-1.10.3\share\julia\stdlib\v1.10\Distributed\src\clusterserialize.jl:72 [inlined]
 [14] foreach
    @ .\abstractarray.jl:3097
 [15] deserialize
    @ D:\Software\julia-1.10.3\share\julia\stdlib\v1.10\Distributed\src\clusterserialize.jl:72
 [16] handle_deserialize
    @ D:\Software\julia-1.10.3\share\julia\stdlib\v1.10\Serialization\src\Serialization.jl:960
 [17] deserialize
    @ D:\Software\julia-1.10.3\share\julia\stdlib\v1.10\Serialization\src\Serialization.jl:814
 [18] handle_deserialize
    @ D:\Software\julia-1.10.3\share\julia\stdlib\v1.10\Serialization\src\Serialization.jl:871
 [19] deserialize
    @ D:\Software\julia-1.10.3\share\julia\stdlib\v1.10\Serialization\src\Serialization.jl:814
 [20] handle_deserialize
    @ D:\Software\julia-1.10.3\share\julia\stdlib\v1.10\Serialization\src\Serialization.jl:874
 [21] deserialize
    @ D:\Software\julia-1.10.3\share\julia\stdlib\v1.10\Serialization\src\Serialization.jl:814 [inlined]
 [22] deserialize_msg
    @ D:\Software\julia-1.10.3\share\julia\stdlib\v1.10\Distributed\src\messages.jl:87
 [23] #invokelatest#2
    @ .\essentials.jl:892 [inlined]
 [24] invokelatest
    @ .\essentials.jl:889 [inlined]
 [25] message_handler_loop
    @ D:\Software\julia-1.10.3\share\julia\stdlib\v1.10\Distributed\src\process_messages.jl:176
 [26] process_tcp_streams
    @ D:\Software\julia-1.10.3\share\julia\stdlib\v1.10\Distributed\src\process_messages.jl:133
 [27] #103
    @ D:\Software\julia-1.10.3\share\julia\stdlib\v1.10\Distributed\src\process_messages.jl:121
Stacktrace:
  [1] (::Base.var"#1033#1035")(x::Task)
    @ Base .\asyncmap.jl:171
  [2] foreach(f::Base.var"#1033#1035", itr::Vector{Any})
    @ Base .\abstractarray.jl:3097
  [3] maptwice(wrapped_f::Function, chnl::Channel{Any}, worker_tasks::Vector{Any}, c::Vector{Any})
    @ Base .\asyncmap.jl:171
  [4] wrap_n_exec_twice
    @ .\asyncmap.jl:147 [inlined]
  [5] #async_usemap#1018
    @ .\asyncmap.jl:97 [inlined]
  [6] async_usemap
    @ .\asyncmap.jl:78 [inlined]
  [7] #asyncmap#1017
    @ .\asyncmap.jl:75 [inlined]
  [8] asyncmap
    @ .\asyncmap.jl:74 [inlined]
  [9] pmap(f::Function, p::Distributed.WorkerPool, c::Vector{…}; distributed::Bool, batch_size::Int64, on_error::Nothing, retry_delays::Vector{…}, retry_check::Nothing)
    @ Distributed D:\Software\julia-1.10.3\share\julia\stdlib\v1.10\Distributed\src\pmap.jl:126
 [10] pmap(f::Function, p::Distributed.WorkerPool, c::Vector{Any})
    @ Distributed D:\Software\julia-1.10.3\share\julia\stdlib\v1.10\Distributed\src\pmap.jl:99
 [11] pmap(f::Function, c::Vector{Any}; kwargs::@Kwargs{})
    @ Distributed D:\Software\julia-1.10.3\share\julia\stdlib\v1.10\Distributed\src\pmap.jl:156
 [12] macro expansion
    @ .\timing.jl:279 [inlined]
 [13] top-level scope
    @ d:\name\MyPkg\test\runtests.jl:35

```

---

<div class="post-metadata">

**Author:** ![jishnub](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/jishnub/32/33620_2.png) [@jishnub](https://discourse.julialang.org/u/jishnub)\
**Post date:** [May 20, 2024, 3:31am UTC](https://discourse.julialang.org/t/keyerror-when-using-pmap/114464/2 "2024-05-20T03:31:49Z")

</div>

You likely need `@everywhere using MyPkg`

---

<div class="post-metadata">

**Author:** ![WuSiren](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/wusiren/32/42529_2.png) [@WuSiren](https://discourse.julialang.org/u/WuSiren)\
**Post date:** [May 20, 2024, 3:37am UTC](https://discourse.julialang.org/t/keyerror-when-using-pmap/114464/3 "2024-05-20T03:37:08Z")

</div>

Oh, I see! All the packaged and variables used in `runtests.jl` should be added `@everywhere`. Is it?

---

<div class="post-metadata">

**Author:** ![WuSiren](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/wusiren/32/42529_2.png) [@WuSiren](https://discourse.julialang.org/u/WuSiren)\
**Post date:** [May 20, 2024, 3:42am UTC](https://discourse.julialang.org/t/keyerror-when-using-pmap/114464/4 "2024-05-20T03:42:19Z")

</div>

> [@jishnub](#):
>
> You likely need `@everywhere using MyPkg`

Sorry, I tried again and it report the same KeyError even I have added ` @everywhere` 🥴