Wiatpid usage code in linux operating system

Wiatpid usage

#include <sys/wait.h>
#include <unistd.h>
#include <stdio.h>

int main() {
  pid_t ret;
  int i, status;
  printf("welcome..pid=%d\n", getpid());
  ret = fork();
  if (ret < 0) {
    perror("fork");
    exit(1);
  }
  if (ret == 0) {
    printf("child--welcome,pid=%d,ppid=%d\n", getpid(), getppid());
    for (i = 1; i <= 5; i++) {
      printf("child--pid=%d,ppid=%d\n", getpid(), getppid());
      usleep(100);
    }
    // exit(5);
    exit(0);
  } else // ret>0
  {
    printf("parent--hello,pid=%d,ppid=%d\n", getpid(), getppid());
    // some work by parent
    waitpid(-1, &status, 0); // wait(&status);
    printf("parent--child exit status=%d\n", WEXITSTATUS(status));
  }
  return 0;
}

 
Notes
 

• Blocks parent process till completion of child process
• Collect exit status of child
• Cleans some pending resources of child (else child will become Zombie)
• waitpid paramaters
  • 1st param : pid of child process waiting for, -1 means any one child
  • 2nd param : status of terminated child (pass by address)
  • 3rd param : flags
• Macros WEXITSTATUS, WIFEXITED to check exit status, normal/abnormal termination

 
Observations & Understanding
 

• Do child process is re parenting to init (adoption by init) after adding waitpid?
• Meaning of 1st parameter to waitpid : -1
• More analysis on child exit status thru waitpid –  WIFEXITED, WIFSIGNALED etc.
• Observations of different ways in which process terminates
  • Normal and Success – exit child with zero
  • Normal and Failure – exit child with non zero, +ve value
  • Abnormal Termination (Try divided by zero or null pointer difference in child)