Added Process exercise's chapter

collatz_shm.c

@@ -0,0 +1,64 @@
+#include <fcntl.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/mman.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+#include <sys/wait.h>
+#include <unistd.h>
+
+#define SIZE 4096
+#define SHM_NAME "collatz"
+
+int collatz(int, void *);
+
+int main(int argc, char *argv[]) {
+  if (argc < 2) {
+    perror("Usage: collatz NUMBER\n");
+    return EXIT_FAILURE;
+  }
+
+  int n = atoi(argv[1]);
+  if (n <= 1) {
+    perror("The number MUST be greater than 1\n");
+    return EXIT_FAILURE;
+  }
+
+  printf("Collatz of %d\n", n);
+
+  // Create memory shared object
+  int fd = shm_open(SHM_NAME, O_CREAT | O_RDWR, 0600);
+  ftruncate(fd, SIZE);
+  void *ptr = (int *)mmap(0, SIZE, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
+
+  pid_t pid = fork();
+  if (pid == 0) {
+    collatz(n, ptr);
+  } else if (pid > 0) {
+    wait(NULL);
+
+    printf("%s\n", (char *)ptr);
+    shm_unlink(SHM_NAME);
+  }
+
+  return EXIT_SUCCESS;
+}
+
+int collatz(int n, void *shm) {
+  char buff[50];
+  sprintf(buff, "%d", n);
+  sprintf(shm, "%s", buff);
+  shm += strlen(buff);
+
+  sprintf(shm, "%s", " ");
+  shm += 1;
+
+  if (n == 1) {
+    return n;
+  } else if (n % 2 == 0) {
+    return collatz(n / 2, shm);
+  } else {
+    return collatz(3 * n + 1, shm);
+  }
+}