c - Grouping child processes with setgpid() -

i don't whole thing.

my process tree:

     0     / \    1   2   /     \  5       3         /         4 

i want make process group (3, 4, 5), , send group signal from, say, 2.

i tried way:

setpgid(pid3, pid3); setpgid(pid4, pid3); setpgid(pid5, pid3);  ...  kill(-pid3, sigusr1); 

where should place setpgid() block? tried placing in 3, 0 , every other process, setpgid()s return either "no such process" or "operation not permitted".

pids stored in files, retrieve them before calling setpgid()

a process can set process group id of only or of children. furthermore, can't change process group id of 1 of children after child has called 1 of exec functions. --apue

in opinion,

1.a grandparent can't use setgpid() gradechild, can check easily.that's say, code in pid 0 below won't work:

setpgid(pid3, pid3);  setpgid(pid4, pid3); setpgid(pid5, pid3); 

2.you can use setgpid() change one's , itselves chilld pgid,you can't write down setpgid(pid5, pid3) in pid 3, because pid 3 , pid 5 aren't parent , child.

so, you'd better use setgpid(someone's pid, pgid) in itself.

but how can 1 process know other processes' pid? method shared memory.

here 1 rough litte complex implement wrote, don't consider process synchronization.it works expected.

#include "stdlib.h"  #include "stdio.h" #include "errno.h" #include "unistd.h" #include "string.h" #include "sys/stat.h" #include "sys/types.h" #include "sys/ipc.h" #include "sys/shm.h" #include "signal.h" #define perm s_irusr|s_iwusr  void sig_usr3(int); void sig_usr4(int); void sig_usr5(int);  int main() {     size_t msize;     key_t shmid;     pid_t *pid;     msize = 6 * sizeof(pid_t);     if( (shmid = shmget(ipc_private, msize , perm)) == -1 )   {          fprintf(stderr, "share memory error:%s\n\a", strerror(errno));         exit(1);     }     pid = shmat(shmid, 0, 0);     memset(pid,0,msize);     pid[0] =  getpid();     //process 0     if(fork() == 0) {     //process 1          pid = shmat(shmid, 0, 0);         pid[1] =  getpid();         if(fork() == 0) {             //process 5             pid = shmat(shmid, 0, 0);             pid[5] =  getpid();             while(pid[3]==0)                 sleep(1);             if((setpgid(pid[5],pid[3]))==-1)                 printf("pid5 setpgid error.\n");             signal(sigusr1,sig_usr5);             for(;;)                  pause();         }         for(;;)              pause();         exit(0);       }      if(fork() == 0) {         //process 2         pid = shmat(shmid, 0, 0);         pid[2] =  getpid();         if(fork() == 0) {             //process 3             pid = shmat(shmid, 0, 0);             pid[3] =  getpid();             if((setpgid(pid[3],pid[3]))==-1)                 printf("pid3 setpgid error.\n");             if(fork() == 0) {                 //process 4                 pid = shmat(shmid, 0, 0);                 pid[4] =  getpid();                 if((setpgid(pid[4],pid[3]))==-1)                     printf("pid4 setpgid error.\n");                 signal(sigusr1,sig_usr4);                 for(;;)                     pause();             }             else {                 signal(sigusr1,sig_usr3);                 for(;;)                       pause();             }             for(;;)                   sleep(100);      }      if(getpid()==pid[0]) {         int i,flag;         while(!(pid[0]&&pid[1]&&pid[2]&&pid[3]&&pid[4]&&pid[5]))             //wait process folking.             sleep(1);          for(i=0;i<6;i++)             printf("process %d,pid:%d\n",i,pid[i]);         kill(-pid[3],sigusr1);     } }  void sig_usr3(int signo) {     if(signo == sigusr1)         printf("recieved sigal in process 3\npid %d\n\n",getpid());     exit(0); }  void sig_usr4(int signo) {     if(signo == sigusr1)         printf("recieved sigal in process 4\npid %d\n\n",getpid());     exit(0); }  void sig_usr5(int signo) {     if(signo == sigusr1)         printf("recieved sigal in process 5\npid %d\n\n",getpid());     exit(0); } 

output:

process 0,pid:31361 process 1,pid:31362 process 2,pid:31363 process 3,pid:31364 process 4,pid:31366 process 5,pid:31365 recieved sigal in process 3 pid 31364  recieved sigal in process 5 pid 31365  recieved sigal in process 4 pid 31366