Alarm signal around popen

Hi all,

I have an issue with getting a timeout to work with popen.

Code:

---

alarm(sig_timeout);
read_fp = popen(system_call,"r"); //call to a system command
if (read_fp != NULL)
{
 chars_read = fread(sys_result, sizeof(char), sizeof(sys_result) - 1, read_fp);       
 pclose(read_fp);
}
alarm(0);

---

The alarm signal is failing to timeout the popen/fread when the system_call hangs. Have I done something wrong?

TIA, rotis23

additional code if needed:

Code:

---

....

struct sigaction action;
int sig_timeout;

....

bzero(&action, sizeof(action));
action.sa_handler = timed_out;
action.sa_flags = 0;
sigaction(SIGALRM, &action, 0);

sig_timeout = 30;

....

alarm(sig_timeout);
read_fp = popen(system_call,"r"); //call to a system command
if (read_fp != NULL)
{
 chars_read = fread(sys_result, sizeof(char), sizeof(sys_result) - 1, read_fp);       
 pclose(read_fp);
}
alarm(0);

---

Is popen() blocking the signal?

thankyou very much VvV, I shall use select.

I'll consider my wrist severely slapped for treading the treacherous path of choosing the wrong board. Please forgive me.

Full marks for noticing my delibarate change for the board of an otherwise perfect variable name.