myshell: Child processes do not run in the background - c

Question

I'm writing myshell program.
it should supportpipe processing. It should also recognize the '&' at the end of the command and run the child process in the background if the '&' is attached.
The problem with my program is,
ls | grep txt works well, but ls | greptxt & is not working.
To this end, I declared globally the pid array that stores the IDs of the generated child processes and the reaped_id array that stores the IDs of the reaped child processes.
The second process are blocked(sigsuspended) if the first child process had not been reapped. Also, when the first process ends, sigchld handler sends a SIGCONT signal to the second process if the second process has been created that moment.
Debugging results in Sigchld handler: it does not send SIGCONT signals to the second process even after the second process has been blocked
More specifically, the incremental pcount (number of child processes created) in the parent process is not reflected in the Sigchld handler.(globally defined) Here's a part of my shell.
while(buffer[idx] != '\0'){
/*check if it is piped process*/
pipe_start_flag = pipe_end_flag; // if last process was piping process, then this process is a piped process
parse_line(&buffer[idx], argv, &idx, &pipe_end_flag); // parse until it meets '\0' or '|'(assign its (index-1) on idx)
pid[pcount] = Fork();
if(pid[pcount] == 0){
int big_bro_idx = pcount - 1; // index of last process
if(!pipe_start_flag && pipe_end_flag){
dup2(fd[WRITEEND],STDOUT_FILENO);
close(fd[READEND]);
}
else if(pipe_start_flag && !pipe_end_flag){
dup2(fd[READEND], STDIN_FILENO);
close(fd[WRITEEND]);
write(STDOUT_FILENO, "second process spawned\n", 23); // debugger
while(reaped_id[big_bro_idx] == 0){ // while last process are executing. If last process terminate, this will be its pid
write(STDOUT_FILENO, "this line works\n", 15); // debugger code
Sigsuspend(&blocking_mask);
}
}
if(execvp(argv[0], argv) < 0){
printf("%s: command not found\n", argv[0]);
exit(1);
}
}
else{ // parent process"
close(fd[WRITEEND]);
if(!bg){
while(reaped_id[pcount] <= 0 && sigtstp_flag == false){
Sigsuspend(&blocking_mask); // wait for sigchld
}
sigtstp_flag = false; // reset flag to false(it changed at sigtstp_flag)
}
else; // background process
write(STDOUT_FILENO, "pcount increased\n", 17); // debugging code
++pcount;
}
++idx;
}
Next is my SIGCHLD handler.
void sigchld_handler(int sig){
sigset_t mask, prev;
int status;
int olderrno = errno;
Sigfillset(&mask);
Sigprocmask(SIG_BLOCK, &mask, &prev);
while((reaped_id[reap_count] = waitpid(-1, &status, WNOHANG)) > 0)
{
write(STDOUT_FILENO, "process terminated\n", 19);
reap_count ++;
}
printf("%d %d %d %d ", pid[reap_count], reap_count, pcount, reaped_id[reap_count -1]);
if(pid[reap_count] > 0 || WIFSTOPPED(status)){ // if there is little brother process
Kill(pid[reap_count], SIGCONT); // send SIGCONT singal to blocked sibling process
write(STDOUT_FILENO, "I alarmed my sibling", 20); // debuggging code; not executed
}
Sigprocmask(SIG_SETMASK, &prev, NULL);
errno = olderrno;
}
process graph:
Shell spawn both child processes
The second process is blocked because the first process is not finished
First process terminated
Sigcont signal should be sent from Sigchld handler to second process but not.
(It shows that the pcount is increased, but when I print a pcount in sigchld handler, it doesn't increase at all.)
I've been up all night for this problem. If you need a full code to execute, we will send it to you.
If there is anything I need to supplement, please tell me and I will supplement it right away.