JuliaParallel
Recv
In mpi-base.jl Recv has the following declaration:
function Recv{T<:MPIDatatype}(::Type{T}, src::Integer, tag::Integer, comm::Comm)
However:
MPI.Recv(Int64, Int(rank + txOffst), Int(i), comm) and MPI.Recv(typeof(rxVal), Int(rank + txOffst), Int(i), comm)
Both throw the error
ERROR: LoadError: MethodError: Recv! has no method matching Recv!(::Type{Ref{Int64}}, ::Int64, ::Int64, ::MPI.Comm)
It appears that Recv calls Recv! which then expects an array type, am I missing something or is this a bug? I notice that there are no tests or examples for sending single objects.
Yes, it seems the definition of Recv! lacks the Ref type; it only handles Ptr and Array. And yes, test coverage is lacking here.
In your examples, the explicit conversions to Int are not necessary.
Perhaps out of ignorance of what is best practice I have omitted any type declaration for the variables i, rank and txOffst. If I do not explicitly convert to an int I found that the function MPI.Send fails with a no matching method error.
Could the issue with Recv be solved in the same way as single object sends appear to be handled in MPI.Send? I.e. function Recv{T<:MPIDatatype}(obj::T, src::Integer, tag::Integer, comm::Comm) buf = [obj] Recv!(buf, src, tag, comm)
That should work, but is less efficient than changing the declaration of Recv! to include Ref as well: Change buf::Union{Ptr{T},Array{T}} there to buf::Union{Ptr{T},Ref{T},Array{T}}. (Untested; will look at it later today.)