fix

Dockerfile

@@ -1,6 +1,6 @@
 FROM debian:stable-slim
 
-# Install g++, make, OpenMPI, AND the OpenSSH server
+# ... (all the apt-get install and ssh setup lines are unchanged) ...
 RUN apt-get update && apt-get install -y --no-install-recommends \
     g++ \
     make \
@@ -9,28 +9,17 @@ RUN apt-get update && apt-get install -y --no-install-recommends \
     openssh-server && \
     rm -rf /var/lib/apt/lists/*
 
-# Create a directory for the SSH daemon to run (use -p to avoid errors)
 RUN mkdir -p /var/run/sshd
-
-# --- SSH Key Generation and Configuration ---
-# Generate a passwordless SSH key pair
 RUN ssh-keygen -t rsa -f /root/.ssh/id_rsa -N ''
-
-# Add the public key to the list of authorized keys for passwordless login
 RUN cat /root/.ssh/id_rsa.pub >> /root/.ssh/authorized_keys
 RUN chmod 600 /root/.ssh/authorized_keys
-
-# --- THIS IS THE NEW LINE ---
-# Create an SSH config file to disable host key checking
 RUN echo "Host *\n\tStrictHostKeyChecking no" >> /root/.ssh/config
-# --- END OF NEW LINE ---
-
-# Allow root login via SSH
 RUN sed -i 's/#PermitRootLogin prohibit-password/PermitRootLogin yes/' /etc/ssh/sshd_config
 
 WORKDIR /app
 
 COPY . /app/
 
-# Compile using the MPI C++ compiler wrapper
+# Compile ALL the necessary tasks during the build
 RUN mpic++ -O2 -std=c++17 -o mpi_task task.cpp
+RUN mpic++ -O2 -std=c++17 -o task1 task1.cpp

docker-compose.yml

@@ -2,16 +2,18 @@ services:
   master:
     build: .
     container_name: pdc-master
+    hostname: pdc-master  # <-- ADD THIS LINE
     volumes:
       - ./hostfile:/app/hostfile
     command: >
-      sh -c "/usr/sbin/sshd & sleep 5 && mpirun -np 4 --hostfile /app/hostfile --allow-run-as-root /app/mpi_task"
+      sh -c "/usr/sbin/sshd & sleep 5 && mpirun -np 5 --hostfile /app/hostfile --allow-run-as-root /app/task1"
     networks:
       - pdcn
 
   worker1:
     build: .
     container_name: pdc-worker1
+    hostname: pdc-worker1  # <-- ADD THIS LINE
     command: /usr/sbin/sshd -D
     networks:
       - pdcn
@@ -19,6 +21,7 @@ services:
   worker2:
     build: .
     container_name: pdc-worker2
+    hostname: pdc-worker2  # <-- ADD THIS LINE
     command: /usr/sbin/sshd -D
     networks:
       - pdcn
@@ -26,6 +29,15 @@ services:
   worker3:
     build: .
     container_name: pdc-worker3
+    hostname: pdc-worker3  # <-- ADD THIS LINE
+    command: /usr/sbin/sshd -D
+    networks:
+      - pdcn
+
+  worker4:
+    build: .
+    container_name: pdc-worker4
+    hostname: pdc-worker4  # <-- ADD THIS LINE
     command: /usr/sbin/sshd -D
     networks:
       - pdcn

hostfile

@@ -2,3 +2,4 @@ master slots=1
 worker1 slots=1
 worker2 slots=1
 worker3 slots=1
+worker4 slots=1

task1.cpp

@@ -0,0 +1,78 @@
+#include <iostream>
+#include <vector>
+#include <mpi.h>
+#include <unistd.h> // Required for gethostname() and getpid()
+
+int main(int argc, char** argv) {
+    MPI_Init(&argc, &argv);
+
+    int world_size;
+    MPI_Comm_size(MPI_COMM_WORLD, &world_size);
+
+    int world_rank;
+    MPI_Comm_rank(MPI_COMM_WORLD, &world_rank);
+
+    // Get the hostname of the container/machine the process is running on.
+    char hostname[256];
+    gethostname(hostname, sizeof(hostname));
+
+    // Get the Process ID of this specific MPI process.
+    pid_t pid = getpid();
+
+    int num_workers = world_size - 1;
+
+    if (world_rank == 0) {
+        // --- MASTER PROCESS ---
+        int data[] = {1, 2, 3, 4};
+        int data_count = sizeof(data) / sizeof(int);
+
+        if (data_count != num_workers) {
+            if (world_rank == 0) { // Only master should print the error
+                std::cerr << "Error: The number of workers (" << num_workers 
+                          << ") must match the number of data elements (" << data_count << ").\n"
+                          << "Please run with -np " << data_count + 1 << " processes." << std::endl;
+            }
+            MPI_Abort(MPI_COMM_WORLD, 1);
+        }
+
+        // Updated print statement to include PID and Hostname
+        std::cout << "Master (rank 0, PID " << pid << " on " << hostname << "): sending numbers 1,2,3,4 to workers..." << std::endl;
+
+        for (int i = 0; i < num_workers; ++i) {
+            int worker_rank = i + 1;
+            MPI_Send(&data[i], 1, MPI_INT, worker_rank, 0, MPI_COMM_WORLD);
+        }
+
+        std::vector<int> results(num_workers);
+        for (int i = 0; i < num_workers; ++i) {
+            int worker_rank = i + 1;
+            int received_result;
+            MPI_Recv(&received_result, 1, MPI_INT, worker_rank, 0, MPI_COMM_WORLD, MPI_STATUS_IGNORE);
+            results[i] = received_result;
+        }
+
+        // Updated print statement
+        std::cout << "Master (rank 0, PID " << pid << " on " << hostname << "): collected results {";
+        for (int i = 0; i < results.size(); ++i) {
+            std::cout << results[i] << (i == results.size() - 1 ? "" : ",");
+        }
+        std::cout << "}" << std::endl;
+
+    } else {
+        // --- WORKER PROCESSES ---
+        int received_number;
+        MPI_Recv(&received_number, 1, MPI_INT, 0, 0, MPI_COMM_WORLD, MPI_STATUS_IGNORE);
+
+        int computed_result = received_number * 10;
+        
+        // Updated print statement to include PID and Hostname
+        std::cout << "Worker (rank " << world_rank << ", PID " << pid << " on " << hostname 
+                  << "): received " << received_number 
+                  << ", computed " << computed_result << std::endl;
+        
+        MPI_Send(&computed_result, 1, MPI_INT, 0, 0, MPI_COMM_WORLD);
+    }
+
+    MPI_Finalize();
+    return 0;
+}