From 1328f599540fc4b2232deb812151ffbeba6fb147 Mon Sep 17 00:00:00 2001
From: Pitesse <pietro.pizzoccheri@mail.polimi.it>
Date: Tue, 3 Dec 2024 18:59:40 +0100
Subject: [PATCH] mpi exercises

---
 .gitignore                                    |  5 +-
 NSDS/MPI/NSDS_MPI_tutorial/src/average.c      | 67 ++++++++++++----
 .../NSDS_MPI_tutorial/src/avoiding_deadlock.c | 29 +++++++
 NSDS/MPI/NSDS_MPI_tutorial/src/filter.c       | 77 +++++++++++++++----
 NSDS/MPI/NSDS_MPI_tutorial/src/hello_world.c  |  8 +-
 NSDS/MPI/NSDS_MPI_tutorial/src/ping_pong.c    | 30 +++++++-
 NSDS/MPI/NSDS_MPI_tutorial/src/probe.c        | 10 +++
 NSDS/MPI/NSDS_MPI_tutorial/src/ring.c         | 24 ++++--
 8 files changed, 209 insertions(+), 41 deletions(-)
 create mode 100644 NSDS/MPI/NSDS_MPI_tutorial/src/avoiding_deadlock.c

diff --git a/.gitignore b/.gitignore
index 593e90c..0ee33cf 100644
--- a/.gitignore
+++ b/.gitignore
@@ -416,4 +416,7 @@ notes.txt
 package-lock.json
 package.json
 
-.DS_Store
\ No newline at end of file
+.DS_Store
+
+NSDS/MPI/NSDS_MPI_tutorial/src/*
+!NSDS/MPI/NSDS_MPI_tutorial/src/*.c
\ No newline at end of file
diff --git a/NSDS/MPI/NSDS_MPI_tutorial/src/average.c b/NSDS/MPI/NSDS_MPI_tutorial/src/average.c
index 85fc94f..d663832 100644
--- a/NSDS/MPI/NSDS_MPI_tutorial/src/average.c
+++ b/NSDS/MPI/NSDS_MPI_tutorial/src/average.c
@@ -4,36 +4,44 @@
 #include <mpi.h>
 
 // Creates an array of random numbers
-int *create_random_array(int num_elements, int max_value) {
-  int *arr = (int *) malloc(sizeof(int)*num_elements);
-  for (int i=0; i<num_elements; i++) {
+int *create_random_array(int num_elements, int max_value)
+{
+  int *arr = (int *)malloc(sizeof(int) * num_elements);
+  for (int i = 0; i < num_elements; i++)
+  {
     arr[i] = (rand() % max_value);
   }
   return arr;
 }
 
 // Computes the average value
-float compute_average(int *array, int num_elements) {
+float compute_average(int *array, int num_elements)
+{
   int sum = 0;
-  for (int i=0; i<num_elements; i++) {
+  for (int i = 0; i < num_elements; i++)
+  {
     sum += array[i];
   }
-  return ((float) sum) / num_elements;
+  return ((float)sum) / num_elements;
 }
 
-// Computes final average value
-float compute_final_average(float *array, int num_elements) {
+// Computes final average value from other averages
+float compute_final_average(float *array, int num_elements)
+{
   float sum = 0.0f;
-  for (int i=0; i<num_elements; i++) {
+  for (int i = 0; i < num_elements; i++)
+  {
     sum += array[i];
   }
-  return  sum/num_elements;
+  return sum / num_elements;
 }
 
-int main(int argc, char** argv) {
+int main(int argc, char **argv)
+{
   // Number of elements for each processor
   int num_elements_per_proc = 1000;
-  if (argc > 1) {
+  if (argc > 1)
+  {
     num_elements_per_proc = atoi(argv[1]);
   }
 
@@ -42,18 +50,45 @@ int main(int argc, char** argv) {
 
   MPI_Init(NULL, NULL);
 
-  int my_rank, world_size; 
+  int my_rank, world_size;
   MPI_Comm_rank(MPI_COMM_WORLD, &my_rank);
   MPI_Comm_size(MPI_COMM_WORLD, &world_size);
 
   // Process 0 creates the array
   int *global_arr = NULL;
-  if (my_rank == 0) {
+  if (my_rank == 0)
+  {
     global_arr = create_random_array(num_elements_per_proc * world_size, 100);
   }
 
-  // TODO
-  
+  // scatter the array
+  int *local_arr = (int *)malloc(sizeof(int) * num_elements_per_proc);
+  MPI_Scatter(global_arr, num_elements_per_proc, MPI_INT, local_arr, num_elements_per_proc, MPI_INT, 0, MPI_COMM_WORLD);
+
+  // compute the average
+  float local_avg = compute_average(local_arr, num_elements_per_proc);
+
+  printf("Process %d has the average: %f\n", my_rank, local_avg);
+
+  // gather all partial averages
+  float *partial_avgs = NULL;
+  if (my_rank == 0)
+  {
+    partial_avgs = (float *)malloc(sizeof(float) * world_size);
+  }
+  MPI_Gather(&local_avg, 1, MPI_FLOAT, partial_avgs, 1, MPI_FLOAT, 0, MPI_COMM_WORLD);
+
+  // p0 computes the final average 
+  if (my_rank == 0)
+  {
+    float final_avg = compute_final_average(partial_avgs, world_size);
+    printf("Final average: %f\n", final_avg);
+    free(partial_avgs);
+    free(global_arr);
+  }
+
+  free(local_arr);
+
   MPI_Barrier(MPI_COMM_WORLD);
   MPI_Finalize();
 }
diff --git a/NSDS/MPI/NSDS_MPI_tutorial/src/avoiding_deadlock.c b/NSDS/MPI/NSDS_MPI_tutorial/src/avoiding_deadlock.c
new file mode 100644
index 0000000..c1c06c8
--- /dev/null
+++ b/NSDS/MPI/NSDS_MPI_tutorial/src/avoiding_deadlock.c
@@ -0,0 +1,29 @@
+#include <mpi.h>
+#include <stdio.h>
+
+// Run with two processes.
+// Process 0 sends an integer to process 1 and vice-versa.
+// Try to run the system: what goes wrong?
+
+// mpicc deadlock.c -o deadlock
+// mpirun -np 2 deadlock
+
+int main(int argc, char **argv)
+{
+    MPI_Init(NULL, NULL);
+
+    int my_rank;
+    MPI_Comm_rank(MPI_COMM_WORLD, &my_rank);
+    int other_rank = 1 - my_rank;
+
+    int msg_to_send = 1;
+    int msg_to_recv;
+
+    // send and receive messages in a non-blocking  way to avoid deadlock
+    MPI_Isend(&msg_to_send, 1, MPI_INT, other_rank, 0, MPI_COMM_WORLD, MPI_REQUEST_NULL);
+    MPI_Irecv(&msg_to_recv, 1, MPI_INT, other_rank, MPI_ANY_TAG, MPI_COMM_WORLD, MPI_REQUEST_NULL);
+
+    printf("Rank %d received message %d from rank %d\n", my_rank, msg_to_recv, other_rank);
+
+    MPI_Finalize();
+}
\ No newline at end of file
diff --git a/NSDS/MPI/NSDS_MPI_tutorial/src/filter.c b/NSDS/MPI/NSDS_MPI_tutorial/src/filter.c
index c6040e5..eb8d128 100644
--- a/NSDS/MPI/NSDS_MPI_tutorial/src/filter.c
+++ b/NSDS/MPI/NSDS_MPI_tutorial/src/filter.c
@@ -4,46 +4,97 @@
 #include <mpi.h>
 
 // Creates an array of random numbers.
-int *create_random_array(int num_elements, int max_value) {
-  int *arr = (int *) malloc(sizeof(int)*num_elements);
-  for (int i=0; i<num_elements; i++) {
+int *create_random_array(int num_elements, int max_value)
+{
+  int *arr = (int *)malloc(sizeof(int) * num_elements);
+  for (int i = 0; i < num_elements; i++)
+  {
     arr[i] = (rand() % max_value);
   }
   return arr;
 }
 
+// gets an array of ints and a number and returns an array containing only the
+// elements that are multiples of the number
+// without knowing how many elements will be in the filtered array
+void filter_array_by_multiples_of_n(int *array, int array_size, int n)
+{
+  for (int i = 0; i < array_size; i++)
+  {
+    if (array[i] % n != 0)
+    {
+      array[i] = -1;
+    }
+  }
+}
+
 // Process 0 selects a number num.
 // All other processes have an array that they filter to only keep the elements
 // that are multiples of num.
 // Process 0 collects the filtered arrays and print them.
-int main(int argc, char** argv) {
+int main(int argc, char **argv)
+{
   // Maximum value for each element in the arrays
   const int max_val = 100;
   // Number of elements for each processor
   int num_elements_per_proc = 50;
   // Number to filter by
   int num_to_filter_by = 2;
-  if (argc > 1) {
+  if (argc > 1)
+  {
     num_elements_per_proc = atoi(argv[1]);
   }
 
-  // Init random number generator
-  srand(time(NULL));
-
   MPI_Init(NULL, NULL);
 
-  int my_rank, world_size; 
+  int my_rank, world_size;
   MPI_Comm_rank(MPI_COMM_WORLD, &my_rank);
   MPI_Comm_size(MPI_COMM_WORLD, &world_size);
 
+  // Seed the random number generator with a different value for each process
+  srand(time(NULL) + my_rank);
+
   // Process 0 selects the num
   int num;
-  if (my_rank == 0) {
+  if (my_rank == 0)
+  {
     num = num_to_filter_by;
   }
 
-  // TODO
-  
+  int *arr = create_random_array(num_elements_per_proc, max_val);
+
+  MPI_Bcast(&num, 1, MPI_INT, 0, MPI_COMM_WORLD);
+
+  filter_array_by_multiples_of_n(arr, num_elements_per_proc, num);
+
+  MPI_Send(arr, num_elements_per_proc, MPI_INT, 0, 0, MPI_COMM_WORLD);
+
+  if (my_rank == 0)
+  {
+    int *filtered_arrs = (int *)malloc(sizeof(int) * num_elements_per_proc * world_size);
+    for (int i = 0; i < world_size; i++)
+    {
+      MPI_Recv(filtered_arrs + i * num_elements_per_proc, num_elements_per_proc, MPI_INT, i, 0, MPI_COMM_WORLD, MPI_STATUS_IGNORE);
+    }
+
+    for (int i = 0; i < world_size; i++)
+    {
+      printf("Filtered array from process %d:\n", i);
+      for (int j = 0; j < num_elements_per_proc; j++)
+      {
+        if(filtered_arrs[i * num_elements_per_proc + j] > 0) {
+          printf("%d ", filtered_arrs[i * num_elements_per_proc + j]);
+        }
+      }
+      printf("\n");
+    }
+
+    free(filtered_arrs);
+  }
+
+  free(arr);
+
   MPI_Barrier(MPI_COMM_WORLD);
   MPI_Finalize();
-}
+  return 0;
+}
\ No newline at end of file
diff --git a/NSDS/MPI/NSDS_MPI_tutorial/src/hello_world.c b/NSDS/MPI/NSDS_MPI_tutorial/src/hello_world.c
index e7b93f1..516f83e 100644
--- a/NSDS/MPI/NSDS_MPI_tutorial/src/hello_world.c
+++ b/NSDS/MPI/NSDS_MPI_tutorial/src/hello_world.c
@@ -1,7 +1,12 @@
 #include <mpi.h>
 #include <stdio.h>
 
-int main(int argc, char** argv) {
+/*
+mpicc hello_world.c -o hello
+mpirun hello
+*/
+
+int main(int argc, char *argv[]) {
   // Init the MPI environment
   MPI_Init(NULL, NULL);
 
@@ -13,6 +18,7 @@ int main(int argc, char** argv) {
   int world_rank;
   MPI_Comm_rank(MPI_COMM_WORLD, &world_rank);
 
+
   // Get the name of the processor
   char processor_name[MPI_MAX_PROCESSOR_NAME];
   int name_len;
diff --git a/NSDS/MPI/NSDS_MPI_tutorial/src/ping_pong.c b/NSDS/MPI/NSDS_MPI_tutorial/src/ping_pong.c
index 0a2cdee..42e79c2 100644
--- a/NSDS/MPI/NSDS_MPI_tutorial/src/ping_pong.c
+++ b/NSDS/MPI/NSDS_MPI_tutorial/src/ping_pong.c
@@ -4,17 +4,39 @@
 
 // Simple ping pong program to exemplify MPI_Send and MPI_Recs
 // Assume only two processes
-int main(int argc, char** argv) {
+int main(int argc, char **argv)
+{
   const int tot_msgs = 100;
-  
+
   MPI_Init(NULL, NULL);
 
   int my_rank;
   MPI_Comm_rank(MPI_COMM_WORLD, &my_rank);
+  int other_rank = 1 - my_rank;
 
   int num_msgs = 0;
 
-  // TODO
-  
+  if (my_rank == 0)
+  {
+    MPI_Ssend(&num_msgs, 1, MPI_INT, other_rank, 0, MPI_COMM_WORLD);
+    printf("Rank %d sent message %d to rank %d\n", my_rank, num_msgs, other_rank);
+  }
+
+  while (num_msgs < tot_msgs)
+  {
+    MPI_Recv(&num_msgs, 1, MPI_INT, other_rank, MPI_ANY_TAG, MPI_COMM_WORLD, MPI_STATUS_IGNORE);
+    printf("Rank %d received message %d from rank %d\n", my_rank, num_msgs, other_rank);
+    num_msgs++;
+    if (num_msgs <= tot_msgs)
+    {
+      MPI_Ssend(&num_msgs, 1, MPI_INT, other_rank, 0, MPI_COMM_WORLD);
+      printf("Rank %d sent message %d to rank %d\n", my_rank, num_msgs, other_rank);
+    }
+    else
+    {
+      break;
+    }
+  }
+
   MPI_Finalize();
 }
diff --git a/NSDS/MPI/NSDS_MPI_tutorial/src/probe.c b/NSDS/MPI/NSDS_MPI_tutorial/src/probe.c
index 6551c11..95c7764 100644
--- a/NSDS/MPI/NSDS_MPI_tutorial/src/probe.c
+++ b/NSDS/MPI/NSDS_MPI_tutorial/src/probe.c
@@ -24,6 +24,16 @@ int main(int argc, char** argv) {
   // Receiver
   else {
     // TODO: check the message size and receive
+    MPI_Status status;
+    MPI_Probe(other_rank, 0, MPI_COMM_WORLD, &status);
+    int num_msgs;
+    MPI_Get_count(&status, MPI_INT, &num_msgs);
+    int *msgs = (int *) malloc(sizeof(int) * num_msgs);
+    MPI_Recv(msgs, num_msgs, MPI_INT, other_rank, 0, MPI_COMM_WORLD, MPI_STATUS_IGNORE);
+    for (int i=0; i<num_msgs; i++) {
+      printf("Received message: %d\n", msgs[i]);
+    }
+    free(msgs);
   }
   
   MPI_Finalize();
diff --git a/NSDS/MPI/NSDS_MPI_tutorial/src/ring.c b/NSDS/MPI/NSDS_MPI_tutorial/src/ring.c
index 1635b35..9271328 100644
--- a/NSDS/MPI/NSDS_MPI_tutorial/src/ring.c
+++ b/NSDS/MPI/NSDS_MPI_tutorial/src/ring.c
@@ -4,7 +4,8 @@
 
 // Send a message in a ring starting from process 0 and increment by one at each hop.
 // When the message gets back to process 0, print the number of hops.
-int main(int argc, char** argv) {
+int main(int argc, char **argv)
+{
   MPI_Init(NULL, NULL);
 
   int my_rank, world_size;
@@ -13,11 +14,22 @@ int main(int argc, char** argv) {
 
   int num_hops = 0;
 
-  // TODO
-  
-  if (my_rank == 0) {
-    printf("Final number of hops in process %d = %d\n", my_rank, num_hops);
+  while (num_hops < world_size)
+  {
+    int hop = 0;
+    MPI_Recv(&hop, 1, MPI_INT, (my_rank - 1), 0, MPI_COMM_WORLD, MPI_STATUS_IGNORE);
+    if (my_rank == 0 && hop == 0)
+    {
+      MPI_Send(&num_hops, 1, MPI_INT, (my_rank + 1), 0, MPI_COMM_WORLD);
+    }
+    num_hops = hop + 1;
+    if (my_rank == 0)
+    {
+      printf("Number of hops in process %d = %d\n", my_rank, num_hops);
+      break;
+    }
+    MPI_Send(&num_hops, 1, MPI_INT, (my_rank + 1) % world_size, 0, MPI_COMM_WORLD);
   }
-  
+
   MPI_Finalize();
 }