From 4ea46657cc73ad74c8b9faaf357748929b9f8403 Mon Sep 17 00:00:00 2001
From: Tuomas Rossi <tuomas.rossi@csc.fi>
Date: Mon, 24 Jun 2024 15:14:50 +0300
Subject: [PATCH] Add demos on testing and probing messages

---
 mpi/demos/send_and_recv_nonblocking_probing.c | 41 +++++++++++++++++
 mpi/demos/send_and_recv_nonblocking_testing.c | 45 +++++++++++++++++++
 mpi/docs/06-non-blocking-communication.md     |  6 +++
 3 files changed, 92 insertions(+)
 create mode 100644 mpi/demos/send_and_recv_nonblocking_probing.c
 create mode 100644 mpi/demos/send_and_recv_nonblocking_testing.c

diff --git a/mpi/demos/send_and_recv_nonblocking_probing.c b/mpi/demos/send_and_recv_nonblocking_probing.c
new file mode 100644
index 000000000..5869ca498
--- /dev/null
+++ b/mpi/demos/send_and_recv_nonblocking_probing.c
@@ -0,0 +1,41 @@
+#include <stdio.h>
+#include <unistd.h>  // for sleep()
+#include <mpi.h>
+
+int main(int argc, char *argv[])
+{
+  int size, rank;
+  MPI_Init(&argc, &argv);
+  MPI_Comm_size(MPI_COMM_WORLD, &size);
+  MPI_Comm_rank(MPI_COMM_WORLD, &rank);
+
+  printf("Hello from rank %d of %d\n", rank, size);
+
+  if (rank == 0) {
+    usleep(100);  // "computing"
+    double data = 42.0;
+
+    // Send with rank 0
+    MPI_Send(&data, 1, MPI_DOUBLE, 1, 0, MPI_COMM_WORLD);
+    printf("Rank %d sent %f\n", rank, data);
+
+  } else if (rank == 1) {
+    int message_waiting;
+    MPI_Status status;
+    MPI_Iprobe(0, 0, MPI_COMM_WORLD, &message_waiting, &status);
+
+    while (!message_waiting) {
+      printf("Rank %d has no incoming messages. Let's do some computing\n", rank);
+      usleep(10);  // "computing"
+      MPI_Iprobe(0, 0, MPI_COMM_WORLD, &message_waiting, &status);
+    }
+
+    printf("Rank %d has incoming message. Let's receive\n", rank);
+    double data;
+    MPI_Recv(&data, 1, MPI_DOUBLE, 0, 0, MPI_COMM_WORLD, &status);
+    printf("Rank %d received %f\n", rank, data);
+
+  }
+
+  MPI_Finalize();
+}
diff --git a/mpi/demos/send_and_recv_nonblocking_testing.c b/mpi/demos/send_and_recv_nonblocking_testing.c
new file mode 100644
index 000000000..6375829d3
--- /dev/null
+++ b/mpi/demos/send_and_recv_nonblocking_testing.c
@@ -0,0 +1,45 @@
+#include <stdio.h>
+#include <unistd.h>  // for sleep()
+#include <mpi.h>
+
+int main(int argc, char *argv[])
+{
+  int size, rank;
+  MPI_Init(&argc, &argv);
+  MPI_Comm_size(MPI_COMM_WORLD, &size);
+  MPI_Comm_rank(MPI_COMM_WORLD, &rank);
+
+  printf("Hello from rank %d of %d\n", rank, size);
+
+  if (rank == 0) {
+    usleep(100);  // "computing"
+    double data = 42.0;
+
+    // Send with rank 0
+    MPI_Send(&data, 1, MPI_DOUBLE, 1, 0, MPI_COMM_WORLD);
+    printf("Rank %d sent %f\n", rank, data);
+
+  } else if (rank == 1) {
+    // Receive with rank 1
+    double data = 0.0;
+    MPI_Request request;
+    MPI_Irecv(&data, 1, MPI_DOUBLE, 0, 0, MPI_COMM_WORLD, &request);
+
+    printf("Rank %d data before wait %f\n", rank, data);
+
+    int completed;
+    MPI_Status status;
+    MPI_Test(&request, &completed, &status);
+    while (!completed) {
+      printf("Rank %d request has not completed. Let's do some computing\n", rank);
+      usleep(10);  // "computing"
+      MPI_Test(&request, &completed, &status);
+    }
+
+    printf("Rank %d request has completed\n", rank);
+    printf("Rank %d received %f\n", rank, data);
+
+  }
+
+  MPI_Finalize();
+}
diff --git a/mpi/docs/06-non-blocking-communication.md b/mpi/docs/06-non-blocking-communication.md
index 982cad022..15350725a 100644
--- a/mpi/docs/06-non-blocking-communication.md
+++ b/mpi/docs/06-non-blocking-communication.md
@@ -106,6 +106,9 @@ MPI_Test(`request`{.input}, `flag`{.output}, `status`{.output})
 - Flag is true if the operation has completed
 - Status of the completed communication is similar to that of `MPI_Recv`
 
+<p>
+- Demo: `send_and_recv_nonblocking_testing.c`
+
 # Test for many non-blocking operations
 
 MPI_Testall(`count`{.input}, `array_of_requests`{.input}, `flag`{.output}, `array_of_statuses`{.output})
@@ -128,6 +131,9 @@ MPI_Iprobe(`source`{.input}, `tag`{.input}, `comm`{.input}, `flag`{.output}, `st
 - `MPI_ANY_SOURCE` can be used for source
 - `MPI_ANY_TAG` can be used for tag
 
+<p>
+- Demo: `send_and_recv_nonblocking_probing.c`
+
 
 # Message probing