Make communication non-blocking by using iSend and iRecv

Fix comment semantics and structure

Add -v verbose check

Signed-off-by: vdhyasani17 <[email protected]>

Author: vdhyasani17

examples/Connectivity.java

@@ -1,51 +1,71 @@
 /*
  * Test the connectivity between all processes
- * WIP
  */
 
 import mpi.*;
+import java.nio.IntBuffer;
 
 class Connectivity {
     public static void main(String args[]) throws MPIException {
         MPI.Init(args);
 
         /*
-         * MPI_COMM_WORLD is the communicator provided when MPI is
+         * MPI.COMM_WORLD is the communicator provided when MPI is
          * initialized. It contains all the processes that are created
          * upon program execution.
          */
         int myRank = MPI.COMM_WORLD.getRank();
         int numProcesses = MPI.COMM_WORLD.getSize();
         Status status;
-        int verbose = 0;
+        boolean verbose = false;
         int peerProcess;
         String processorName = MPI.getProcessorName();
 
+        for (String arg : args) {
+            if (arg.equals("-v") || arg.equals("--verbose")) {
+                verbose = true;
+                break;
+            }
+        }
+
         for (int i = 0; i < numProcesses; i++) {
-            if (myRank == i) { /* Find current process */
+            /* Find current process */
+            if (myRank == i) {
                 /* send to and receive from all higher ranked processes */
                 for (int j = i + 1; j < numProcesses; j++) {
-                    if (verbose != 0)
+                    if (verbose)
                         System.out.printf("Checking connection between rank %d on %s and rank %d\n", i, processorName,
                                 j);
 
-                    int[] dataBuffer = { myRank }; /*
-                                                    * Data buffer to be sent to next process (in this case, only send
-                                                    * rank num)
-                                                    */
-                    int[] recBuffer = new int[1]; /* Data buffer that current process receives from previous process */
+                    /*
+                     * rank is the Buffer passed into iSend to send to rank j.
+                     * rank is populated with myRank, which is the data to send off
+                     * peer is the Buffer received from rank j from iRecv
+                     */
+                    IntBuffer rank = MPI.newIntBuffer(1);
+                    IntBuffer peer = MPI.newIntBuffer(1);
+                    rank.put(0, myRank);
 
-                    /* Process must send message first then wait to receive to avoid deadlock */
-                    MPI.COMM_WORLD.send(dataBuffer, 1, MPI.INT, j, myRank);
-                    MPI.COMM_WORLD.recv(recBuffer, 1, MPI.INT, j, j);
+                    /*
+                     * To avoid deadlocks, use non-blocking communication iSend and iRecv
+                     * This will allow the program to progress, in the event that
+                     * two ranks both send to each other at the same time and could
+                     * potentially cause deadlock. The ranks can send their requests
+                     * without halting the program and immediately
+                     */
+                    Request sendReq = MPI.COMM_WORLD.iSend(rank, 1, MPI.INT, j, myRank);
+                    Request recvReq = MPI.COMM_WORLD.iRecv(peer, 1, MPI.INT, j, j);
+                    sendReq.waitFor();
+                    recvReq.waitFor();
                 }
             } else if (myRank > i) {
-                int[] dataBuffer = { myRank };
-                int[] recBuffer = new int[1];
+                IntBuffer rank = MPI.newIntBuffer(1);
+                IntBuffer peer = MPI.newIntBuffer(1);
+                rank.put(0, myRank);
 
                 /* receive from and reply to rank i */
-                MPI.COMM_WORLD.recv(recBuffer, 1, MPI.INT, i, i);
-                MPI.COMM_WORLD.send(dataBuffer, 1, MPI.INT, i, myRank);
+                MPI.COMM_WORLD.iRecv(peer, 1, MPI.INT, i, i).waitFor();
+                MPI.COMM_WORLD.iSend(rank, 1, MPI.INT, i, myRank).waitFor();
             }
         }