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  1. #include <stdio.h>
  2. #include <stdlib.h>
  3. #include <unistd.h>
  4. #include <signal.h>
  5.  
  6. int N = 5;
  7. int _pipe[2];
  8. pid_t children[5];
  9.  
  10. int main(){
  11.     pid_t parent_pid;
  12.     pid_t pid;
  13.     int i = 0;
  14.     int return_val; //we're not going to use this, but need it to call sigwait()
  15.  
  16.     sigset_t set;
  17.     sigfillset(&set);
  18.     sigprocmask(SIG_BLOCK, &set, NULL);
  19.  
  20.     parent_pid = getpid();
  21.     fprintf(stderr,"I am main process, here comes my pid %u\n",getpid());
  22.  
  23.     if (0>pipe(_pipe)) fprintf(stderr,"Error when creating pipe");
  24.  
  25.     //Start creating child processes
  26.     while (i < N){
  27.             pid = fork();
  28.             if (pid == 0){
  29.                 close(_pipe[1]);
  30.             break;
  31.         }
  32.         else{
  33.             fprintf(stderr,"Created child with pid %u\n",pid);
  34.             children[i] = pid;
  35.             write(_pipe[1],&pid,sizeof(pid_t));
  36.         }
  37.         i = i+1;
  38.     }
  39.  
  40.     i = 0;
  41.  
  42.     // What main process does
  43.     if (pid>0){
  44.         close(_pipe[0]);
  45.         close(_pipe[1]);
  46.  
  47.         //sleep(2);
  48.  
  49.         // Main process sends signal to each child
  50.         while(i < N){           
  51.             kill(children[i],SIGUSR1);
  52.             fprintf(stderr,"Sent SIGUSR1 to child %u\n",children[i]);
  53.             // .. Now just wait for SIGUSR2 arrival
  54.             sigwait(&set, &return_val);
  55.  
  56.             i = i+1;
  57.         }
  58.     }
  59.     // What children do
  60.     else{
  61.         // Wait for main process SIGUSR1 delivery
  62.         sigwait(&set, &return_val);
  63.  
  64.         fprintf(stderr, "SIGUSR1 arrived child %u from its father\n",getpid());
  65.  
  66.         // Once SIGUSR1 has arrived, pipe is read N times
  67.         while((i < N) && (read(_pipe[0],&pid,sizeof(pid_t))>0)){
  68.             children[i] = pid;
  69.             i = i+1;
  70.         }
  71.         close(_pipe[0]);
  72.  
  73.         // After reading pipe, a reply is sent to parent process
  74.         kill(parent_pid,SIGUSR2);
  75.     }
  76.  
  77.     return 0;
  78. }
Success #stdin #stdout 0.01s 1716KB
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https://ideone.com/TRcqga
language:
C (gcc 8.3)
created:
11 years ago
visibility:
public

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