Processes

EXAMPLE: count.c

#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>

main(int argc, char *argv[])
{
  int i, max;

  if (argc == 1)
    max = 100;
  else
    max = atoi(argv[1]);

  for (i=1; i<=max; i++) {
    printf("%d\n", i);
    sleep(1);
  }
}

EXEC

• Exec():
  execl(path, arg0, arg1, ..., 0);

must terminate with 0. arg0 must be the executable name.

#include<stdio.h>
#include <unistd.h>

int main()
{
  int ret=execl("./count", "count", "4", 0);
  printf("ERROR !! exec returned: %d\n", ret);
}

EXECV

• Exec():
  execv(path, A);

as above, but
A[0] = arg0,
A[1] = arg1, ...
A[n] = 0.

#include<stdio.h>
#include <unistd.h>

int main()
{
  char* A[3];

  A[0] = "count";
  A[1] = "4";
  A[2] = 0;

  /* here we pass an array of strings */
  int ret = execv("./count",A);

  printf("ERROR !! exec returned: %d\n", ret);
}

FORK

• Fork():
  childpid = fork();

child process gets childpid == 0,
parent gets the child's process id

#include <stdio.h>
#include <unistd.h>
main()
{
  int pchild,i;

  pchild=fork();
  if (pchild ==0) {
    //I'm the child
    int ret=execl("./count", "count", "4", 0);
    printf("ERROR !! exec returned: %d\n", ret);
  }
  // I'm the parent
  for(i=0;i<8;i++) {
    printf("parent: %d\n", i);
    sleep(1);
  }
}

WAIT

• Waitpid():
  waitpid(pid,&status,0);

#include <sys/wait.h>
#include <stdio.h>
#include <unistd.h>
main()
{
  int pchild,i;
  int status;

  pchild=fork();
  if (pchild ==0) {
    //I'm the child
    int ret=execl("./count", "count", "4", 0);
    printf("ERROR !! exec returned: %d\n", ret);
  }
  // I'm the parent
  waitpid(pchild,&status,0);
  for(i=0;i<8;i++) {
    printf("parent: %d\n", i);
    sleep(1);
  }
}