c - trouble with forking 3 grandchildren from children, order and PID and PPIDs not right -


hi have question creating more children fork() based upon earlier question asked using fork() make 3 children out of 1 parent in c (not c++)

i want output (#s simplfied , used illustrate order)

[grandpa]hi pid 1234 , come ####(dont care number is)   [dad] hi pid 2111 , come ppid 1234     [son] hi pid 3111 , come ppid 2111     [son] hi pid 3112 , come ppid 2111     [son] hi pid 3113 , come ppid 2111   [dad] hi pid 2112 , come ppid 1234     [son] hi pid 3111 , come ppid 2112     [son] hi pid 3112 , come ppid 2112     [son] hi pid 3113 , come ppid 2112   [dad] hi pid 2113 , come ppid 1234     [son] hi pid 3111 , come ppid 2113     [son] hi pid 3112 , come ppid 2113     [son] hi pid 3113 , come ppid 2113

but output looks this:

output

it seems ok @ end there regards dad ppid except last 1 , of pids seem out of order. don't know why there 1 son, 5, 3 sons. here code:

int grandforking(null) {     gen1 (null);            return 0; }  int gen1 (null) {       void about(char *);   int i=0;   int j=0;     about("grandpa");       for(i = 0; < 3; i++ )   {         pid_t child = 0;         child = fork();         if (child < 0)          { //unable fork error             perror ("unable fork");             exit(-1);         }             else if (child == 0)         { //child process              gen2 (null);              exit(0);         }             else          { //parent process                   //(do nothing)         }       }      for(j = 0; j < 3; j++ )   {      wait(null);//wait parent acknowledge child process   } return 0; }  int gen2 (null) {      int i=0;   int j=0;   about("dad");   for(i = 0; < 3; i++ )   {         pid_t child = 0;         child = fork();         if (child < 0)         { //unable fork error             perror ("unable fork");             exit(-1);          }              else if (child == 0)          { //child process              ("son");              exit(0);          }             else           { //parent process             //(do nothing)          }   }   for(j = 0; j < 3; j++ )   {     wait(null);//wait parent acknowledge child process   }    return 0;      }

once processes launched, scheduler can , run them in order wishes. includes running several @ same time, if have more 1 processor. (like everyone, these days.)

it can launch child, run child while, , go parent print message.

you'd better ordering if had identifying printf before parent spawned children.

but way you'll lockstep ordering if like:

  • identify oneself
  • start of loop
    • launch child
    • wait child complete
  • exit after children have completed

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