From 8b4bbbcd950a89ba3fdbaa1a99fbd17ee9914232 Mon Sep 17 00:00:00 2001
From: Erik Schnetter <schnetter@gmail.com>
Date: Tue, 8 Sep 2026 13:16:31 -0400
Subject: [PATCH 1/2] Dist_graph_create*: Finalize the created communicators

---
 src/topology.jl            |  7 ++++++-
 test/test_neighbor_comm.jl | 27 +++++++++++++++++++++++++++
 2 files changed, 33 insertions(+), 1 deletion(-)

diff --git a/src/topology.jl b/src/topology.jl
index 5ace5bb19..b24d54f76 100644
--- a/src/topology.jl
+++ b/src/topology.jl
@@ -198,6 +198,8 @@ const WEIGHTS_EMPTY = WeightsEmpty()
 
 Create a new communicator from a given directed graph topology, described by local incoming and outgoing edges on an existing communicator.
 
+[`MPI.free`](@ref) may be called on the returned communicator once it is no longer needed; otherwise it is freed at finalization.
+
 # Arguments
 - `comm::Comm`: The communicator on which the distributed graph topology should be induced.
 - `sources::Vector{Cint}`: The local, incoming edges on the rank of the calling process.
@@ -229,6 +231,7 @@ function Dist_graph_create_adjacent(comm::Comm, sources::Vector{Cint}, destinati
                                        length(sources), sources, source_weights,
                                        length(destinations), destinations, destination_weights,
                                        Info(infokws...), reorder, graph_comm)
+    graph_comm != COMM_NULL && finalizer(free, graph_comm)
     return graph_comm
 end
 
@@ -237,6 +240,8 @@ end
 
 Create a new communicator from a given directed graph topology, described by incoming and outgoing edges on an existing communicator.
 
+[`MPI.free`](@ref) may be called on the returned communicator once it is no longer needed; otherwise it is freed at finalization.
+
 # Arguments
 - `comm::Comm`: The communicator on which the distributed graph topology should be induced.
 - `sources::Vector{Cint}`: An array with the ranks for which this call will specify outgoing edges.
@@ -266,7 +271,7 @@ function Dist_graph_create(comm::Comm, sources::Vector{Cint}, degrees::Vector{Ci
     #                           MPI_Info info, int reorder, MPI_Comm *comm_dist_graph)
     API.MPI_Dist_graph_create(comm, length(sources), sources, degrees, destinations, weights,
                               Info(infokws...), reorder, graph_comm)
-
+    graph_comm != COMM_NULL && finalizer(free, graph_comm)
     return graph_comm
 end
 
diff --git a/test/test_neighbor_comm.jl b/test/test_neighbor_comm.jl
index 4dcb25a5a..fdeaf92bf 100644
--- a/test/test_neighbor_comm.jl
+++ b/test/test_neighbor_comm.jl
@@ -53,5 +53,32 @@ let
     @test srcw2 == srcw3 == Cint[prev_rank + comm_size]
 end
 
+# Both `Dist_graph_create*` must attach a finalizer, like every other
+# communicator constructor, so that the communicator is not leaked.
+let
+    graph_comm = ring_graph(; weighted=false)
+    @test graph_comm != MPI.COMM_NULL
+    finalize(graph_comm)
+    @test graph_comm == MPI.COMM_NULL
+end
+
+let
+    sources = Cint[prev_rank]
+    destinations = Cint[next_rank]
+    graph_comm = MPI.Dist_graph_create_adjacent(comm, sources, destinations)
+    @test graph_comm != MPI.COMM_NULL
+    finalize(graph_comm)
+    @test graph_comm == MPI.COMM_NULL
+end
+
+# An explicit `free` must compose with the finalizer rather than double-free.
+let
+    graph_comm = ring_graph(; weighted=false)
+    MPI.free(graph_comm)
+    @test graph_comm == MPI.COMM_NULL
+    finalize(graph_comm)
+    @test graph_comm == MPI.COMM_NULL
+end
+
 MPI.Finalize()
 @test MPI.Finalized()

From 6c0bc1fb2e580bc0f71c72107a4a94284f64b04e Mon Sep 17 00:00:00 2001
From: Erik Schnetter <schnetter@gmail.com>
Date: Tue, 22 Sep 2026 10:24:15 -0400
Subject: [PATCH 2/2] Remove test for `COMM_NULL`

---
 src/topology.jl | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/src/topology.jl b/src/topology.jl
index b24d54f76..ea0a850b0 100644
--- a/src/topology.jl
+++ b/src/topology.jl
@@ -231,7 +231,7 @@ function Dist_graph_create_adjacent(comm::Comm, sources::Vector{Cint}, destinati
                                        length(sources), sources, source_weights,
                                        length(destinations), destinations, destination_weights,
                                        Info(infokws...), reorder, graph_comm)
-    graph_comm != COMM_NULL && finalizer(free, graph_comm)
+    finalizer(free, graph_comm)
     return graph_comm
 end
 
@@ -271,7 +271,7 @@ function Dist_graph_create(comm::Comm, sources::Vector{Cint}, degrees::Vector{Ci
     #                           MPI_Info info, int reorder, MPI_Comm *comm_dist_graph)
     API.MPI_Dist_graph_create(comm, length(sources), sources, degrees, destinations, weights,
                               Info(infokws...), reorder, graph_comm)
-    graph_comm != COMM_NULL && finalizer(free, graph_comm)
+    finalizer(free, graph_comm)
     return graph_comm
 end