Setting default algorithm to discover the communication graph

Project.toml

@@ -12,6 +12,7 @@ FillArrays = "1a297f60-69ca-5386-bcde-b61e274b549b"
 IterativeSolvers = "42fd0dbc-a981-5370-80f2-aaf504508153"
 LinearAlgebra = "37e2e46d-f89d-539d-b4ee-838fcccc9c8e"
 MPI = "da04e1cc-30fd-572f-bb4f-1f8673147195"
+Preferences = "21216c6a-2e73-6563-6e65-726566657250"
 Printf = "de0858da-6303-5e67-8744-51eddeeeb8d7"
 Random = "9a3f8284-a2c9-5f02-9a11-845980a1fd5c"
 SparseArrays = "2f01184e-e22b-5df5-ae63-d93ebab69eaf"
@@ -26,6 +27,7 @@ Distances = "0.10"
 FillArrays = "0.10, 0.11, 0.12, 0.13, 1"
 IterativeSolvers = "0.9"
 MPI = "0.16, 0.17, 0.18, 0.19, 0.20"
+Preferences = "1"
 SparseMatricesCSR = "0.6"
 StaticArrays = "1"
 julia = "1.1"

src/PartitionedArrays.jl

@@ -11,6 +11,10 @@ import IterativeSolvers
 import Distances
 using BlockArrays
 using Adapt
+using Preferences
+
+export set_default_find_rcv_ids
+include("preferences.jl")
 
 export length_to_ptrs!
 export rewind_ptrs!

src/mpi_array.jl

@@ -660,9 +660,14 @@ end
 Issend(data, dest::Integer, tag::Integer, comm::MPI.Comm, req=MPI.Request()) =
     Issend(MPI.Buffer_send(data), dest, tag, comm, req)
 
-
 function default_find_rcv_ids(::MPIArray)
-    find_rcv_ids_gather_scatter
+    @static if default_find_rcv_ids_algorithm == "gather_scatter"
+        find_rcv_ids_gather_scatter
+    elseif default_find_rcv_ids_algorithm == "ibarrier"
+        find_rcv_ids_ibarrier
+    else
+        error("Unknown algorithm: $(default_find_rcv_ids_algorithm)")
+    end
 end
 
 """

src/preferences.jl

@@ -0,0 +1,28 @@
+
+"""
+    set_default_find_rcv_ids(algorithm::String)
+
+Sets the default algorithm to discover communication neighbors. The available algorithms are:
+
+- `gather_scatter`: Gathers neighbors in a single processor, builds the communications graph 
+  and then scatters the information back to all processors.
+
+- `ibarrier`: Implements Alg. 2 in https://dl.acm.org/doi/10.1145/1837853.1693476
+
+Feature only available in Julia 1.6 and later due to restrictions from `Preferences.jl`.
+"""
+function set_default_find_rcv_ids(algorithm::String)
+    if !(algorithm in ("gather_scatter", "ibarrier"))
+        throw(ArgumentError("Invalid algorihtm: \"$(algorithm)\""))
+    end
+
+    # Set it in our runtime values, as well as saving it to disk
+    @set_preferences!("default_find_rcv_ids" => algorithm)
+    @info("New deafult algorithm set; restart your Julia session for this change to take effect!")
+end
+
+@static if VERSION >= v"1.6"
+    const default_find_rcv_ids_algorithm = @load_preference("default_find_rcv_ids", "gather_scatter")
+else
+    const default_find_rcv_ids_algorithm = "gather_scatter"
+end