Assignment 1

prog.c

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+/* Write a C program prog.c that creates a tree of processes in order to
+recursively compute the maximum in an array of integers. The process at the root
+of the tree reads the count n of integers in the array as a command-line parameter.
+An array A of size n is then populated with randomly generated integers of small
+value (in the range 0-127). The initially unsorted array is printed by the root
+process. Any process in the tree handles a chunk of the array A. The chunk is
+delimited by two indices L and R. For the root process, L=0 and R=n-1.
+
+Any process P in the tree (including the root) first counts the number of integers
+in the chunk it has got. If that count is less than 10, then the process itself
+computes the maximum element in its chunk, prints it and exits. If the chunk size
+of P is 10 or more, then P creates two child processes PL and PR which handle the
+chunks [L, M] and [M+1, R] in A respectively, where M = (L+R)/2. P waits until the
+two child processes PL and PR exit. It then computes the maximum of the two maximum
+values computed by PL and PR, prints the maximum and exits.
+
+Every non-root process returns to its parent (via the exit status) the maximum
+value of its chunk. During the printing of the maximum by a process P, the PID
+and the parent PID of P are also printed. The code is expected to handle values
+in the range of 50 - 100.
+*/
+
+#include <stdio.h>
+#include <unistd.h>
+#include <stdlib.h>
+#include <time.h>
+#include <sys/types.h>
+#include <sys/wait.h>
+
+#define MIN_SIZE 50
+#define MAX_SIZE 100
+
+int *A;
+
+int getMax(int l, int r) {
+  int max = -1;
+  for (int i = l ; i <= r ; ++i)
+    max = max > A[i] ? max : A[i];
+  return max;
+}
+
+int recurFindMax(int l, int r) {
+  if (r-l < 10) {
+    printf("Current process: %u, Parent process: %u\n", getpid(), getppid());
+    return getMax(l, r);
+  }
+
+  int pid1, pid2, status1, status2;
+
+  if ((pid1 = fork()) == 0)
+    exit(recurFindMax(l, (l+r)/2));
+  else {
+    if ((pid2 = fork()) == 0)
+      exit(recurFindMax((l+r)/2, r));
+    else {
+      waitpid(pid1, &status1, 0);
+      waitpid(pid2, &status2, 0);
+      status1 = WEXITSTATUS(status1);
+      status2 = WEXITSTATUS(status2);
+
+      printf("Current process: %u, Parent process: %u\n", getpid(), getppid());
+      return status1 > status2 ? status1 : status2;
+    }
+  }
+}
+
+int main(int argc, char* argv[]) {
+  int n = atoi(argv[1]);
+  if (n < MIN_SIZE && n > MAX_SIZE) {
+    printf("The value of n should be between %d and %d\n", MIN_SIZE, MAX_SIZE);
+    exit(1);
+  }
+  A = (int*)malloc(n*sizeof(int));
+  srand((unsigned int)time(NULL));
+
+  for (int i = 0 ; i < n ; ++i)
+    A[i] = rand() % 128;
+
+  printf("A[] = ");
+  for (int i = 0 ; i < n ; ++i)
+    printf("%d ", A[i]);
+  printf("\n");
+
+  int res = recurFindMax(0, n-1);
+  printf("The maximum value in the array is %d\n", res);
+
+  return 0;
+}