SharedArray(Void, 1) errors

[mauro3]

SharedArray(Void, 1) errors on 0.5:

   _       _ _(_)_     |  A fresh approach to technical computing
  (_)     | (_) (_)    |  Documentation: http://docs.julialang.org
   _ _   _| |_  __ _   |  Type "?help" for help.
  | | | | | | |/ _` |  |
  | | |_| | | | (_| |  |  Version 0.5.0-dev+4754 (2016-06-14 05:04 UTC)
 _/ |\__'_|_|_|\__'_|  |  Commit dab5c8d* (7 days old master)
|__/                   |  x86_64-pc-linux-gnu

julia> SharedArray(Void, 1)
ERROR: BoundsError: attempt to access 0-element Array{Void,1} at index [1:1]
 in throw_boundserror(::Array{Void,1}, ::Tuple{UnitRange{Int64}}) at ./abstractarray.jl:281
 in checkbounds at ./abstractarray.jl:290 [inlined]
 in sub at ./subarray.jl:121 [inlined]
 in sub_1dim(::SharedArray{Void,1}, ::Int64) at ./sharedarray.jl:329
 in init_loc_flds(::SharedArray{Void,1}) at ./sharedarray.jl:341
 in initialize_shared_array(::SharedArray{Void,1}, ::Array{Void,1}, ::Bool, ::Bool, ::Array{Int64,1}) at ./sharedarray.jl:200
 in #SharedArray#446(::Bool, ::Array{Int64,1}, ::Type{T}, ::Type{T}, ::Tuple{Int64}) at ./sharedarray.jl:100
 in #SharedArray#451(::Array{Any,1}, ::Type{T}, ::Type{T}, ::Int64, ::Vararg{Int64,N}) at ./sharedarray.jl:111
 in SharedArray{T,N}(::Type{T}, ::Int64) at ./sharedarray.jl:111
 in eval(::Module, ::Any) at ./boot.jl:225
 in macro expansion at ./REPL.jl:92 [inlined]
 in (::Base.REPL.##1#2{Base.REPL.REPLBackend})() at ./event.jl:46

and 0.4:

   _       _ _(_)_     |  A fresh approach to technical computing
  (_)     | (_) (_)    |  Documentation: http://docs.julialang.org
   _ _   _| |_  __ _   |  Type "?help" for help.
  | | | | | | |/ _` |  |
  | | |_| | | | (_| |  |  Version 0.4.6 (2016-06-19 17:16 UTC)
 _/ |\__'_|_|_|\__'_|  |  
|__/                   |  x86_64-pc-linux-gnu

julia> SharedArray(Void, 1)
ERROR: ArgumentError: requested size must be > 0, got 0
 in tryparse_internal at ./parse.jl:118
 in tryparse_internal at ./parse.jl:136
 in parse at parse.jl:146
 in print_shmem_limits at sharedarray.jl:463
 in shm_mmap_array at sharedarray.jl:490
 in __SharedArray#138__ at sharedarray.jl:58
 in SharedArray at sharedarray.jl:117

[amitmurthy]

The size of the required shmem segment is calculated by multiplying the size of the element type with the size of the array.

The issue is isbits(Void) is true and sizeof(Void) is 0.

We should probably not allow shared arrays of type Void.

[mauro3]

Note, all other singleton immutables also have this property too (and throw the same errors).

For generic programming it would be nice to have this work, although special casing is not the end of the world. But for sure, a better error message.

[amitmurthy]

Yes, for zero sized types, we shouldn't actually create and map any segment but just have local arrays of the requested type. Should work.

[mauro3]

Thanks! Could this be back-ported?

[amitmurthy]

Marking it for back-porting though I don't know if are going to have a 0.4.7 anytime soon.

[amitmurthy]

Marking it on the PR.