From ae33518ca5bca7d18ea6d0c21eb83647acca649c Mon Sep 17 00:00:00 2001
From: Fredrik Ekre <ekrefredrik@gmail.com>
Date: Wed, 27 Jul 2022 18:42:41 +0200
Subject: [PATCH] Use COMM_SELF for single process solves.

---
 docs/src/hypre-matrix-vector.md | 2 +-
 src/HYPRE.jl                    | 6 +++---
 test/runtests.jl                | 6 +++---
 3 files changed, 7 insertions(+), 7 deletions(-)

diff --git a/docs/src/hypre-matrix-vector.md b/docs/src/hypre-matrix-vector.md
index 0bc30a1..ea3b813 100644
--- a/docs/src/hypre-matrix-vector.md
+++ b/docs/src/hypre-matrix-vector.md
@@ -27,7 +27,7 @@ based it can be *slightly* more resource efficient to use `SparseMatrixCSR`.
 The constructors also support both PartitionedArrays.jl backends: When using the `MPI`
 backend the communicator of the `PSparseMatrix`/`PVector` is used also for the
 `HYPREMatrix`/`HYPREVector`, and when using the `Sequential` backend it is assumed to be a
-single-process setup, and the global communicator `MPI.COMM_WORLD` is used.
+single-process setup, and the `MPI.COMM_SELF` communicator is used.
 
 **Example pseudocode**
 
diff --git a/src/HYPRE.jl b/src/HYPRE.jl
index 9af147f..f8da68c 100644
--- a/src/HYPRE.jl
+++ b/src/HYPRE.jl
@@ -243,7 +243,7 @@ function HYPREMatrix(comm::MPI.Comm, B::Union{SparseMatrixCSC,SparseMatrixCSR},
 end
 
 HYPREMatrix(B::Union{SparseMatrixCSC,SparseMatrixCSR}, ilower=1, iupper=size(B, 1)) =
-    HYPREMatrix(MPI.COMM_WORLD, B, ilower, iupper)
+    HYPREMatrix(MPI.COMM_SELF, B, ilower, iupper)
 
 #########################
 # Vector -> HYPREVector #
@@ -266,7 +266,7 @@ function HYPREVector(comm::MPI.Comm, x::Vector, ilower, iupper)
 end
 
 HYPREVector(x::Vector, ilower=1, iupper=length(x)) =
-    HYPREVector(MPI.COMM_WORLD, x, ilower, iupper)
+    HYPREVector(MPI.COMM_SELF, x, ilower, iupper)
 
 # TODO: Other eltypes could be support by using a intermediate buffer
 function Base.copy!(x::Vector{HYPRE_Complex}, h::HYPREVector)
@@ -376,7 +376,7 @@ end
 function Internals.get_comm(A::Union{PSparseMatrix{<:Any,<:M}, PVector{<:Any,<:M}}) where M <: MPIData
     return A.rows.partition.comm
 end
-Internals.get_comm(_::Union{PSparseMatrix,PVector}) = MPI.COMM_WORLD
+Internals.get_comm(_::Union{PSparseMatrix,PVector}) = MPI.COMM_SELF
 
 function Internals.get_proc_rows(A::Union{PSparseMatrix{<:Any,<:M}, PVector{<:Any,<:M}}) where M <: MPIData
     r = A.rows.partition.part
diff --git a/test/runtests.jl b/test/runtests.jl
index f07d05a..c3a9d23 100644
--- a/test/runtests.jl
+++ b/test/runtests.jl
@@ -73,13 +73,13 @@ end
     H = HYPREMatrix(CSC)
     @test H.ijmatrix != HYPRE_IJMatrix(C_NULL)
     @test H.parmatrix != HYPRE_ParCSRMatrix(C_NULL)
-    @test H.comm == MPI.COMM_WORLD
+    @test H.comm == MPI.COMM_SELF
     @test H.ilower == H.jlower == 1
     @test H.iupper == H.jupper == 10
     H = HYPREMatrix(CSR)
     @test H.ijmatrix != HYPRE_IJMatrix(C_NULL)
     @test H.parmatrix != HYPRE_ParCSRMatrix(C_NULL)
-    @test H.comm == MPI.COMM_WORLD
+    @test H.comm == MPI.COMM_SELF
     @test H.ilower == H.jlower == 1
     @test H.iupper == H.jupper == 10
 end
@@ -214,7 +214,7 @@ end
     h = HYPREVector(b)
     @test h.ijvector != HYPRE_IJVector(C_NULL)
     @test h.parvector != HYPRE_ParVector(C_NULL)
-    @test h.comm == MPI.COMM_WORLD
+    @test h.comm == MPI.COMM_SELF
     @test h.ilower == 1
     @test h.iupper == 10