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geta
Apprentice
Joined: 10 May 2003
Posts: 153
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 Posted: Wed Sep 17, 2003 9:58 pm Post subject: signal handling and glibc |
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UPDATE: By including some output messages I've rooted the problem down to wrong file flags, which locked up read() in my sigio handler. Although I set the O_NONBLOCK attribute I didn't set it in a clean fashion. So my questions from earlier on are solved.
But there has been an other question popping up. Why does Linux keep sending a few dozen of SIGIOs per second, although there's no input at any of the opened ports?
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Being a newbie at implementing (programming) inter-process features, I've got some problems related to signal handling, which neither the glibc-manual nor google could give me any answers to.
Here's my programme. It opens one real serial port (/dev/ttySx) and a terminal (/dev/pts/x). As soon as input arrives (signalled by a SIGIO) it reads out both ports (it cannot distiguish, which port sent the signal), displays the content and sends the content on to the other port.
| Code: | #include <stdio.h> // printf, scanf
#include <termios.h> // needed for termios struct
#include <unistd.h> // needed for termios struct and getpid()
#include <fcntl.h> // needed by open(,,) and for I/O modes (sigio)
#include <stdlib.h> // needed by close()
#include <string.h>
#include <signal.h> // IPC signals
#include <sys/types.h> // to get PID of this process |
some variables, then define signal handlers:
| Code: | void term_handler(int sig){...}
void sigint_handler(int sig){...}
void port_handler(int sig){...//print data and copy to other port} |
then cleanup(), then main:
| Code: | int main (){
atexit(cleanup);
signal(SIGIO, port_handler);
signal(SIGTERM, term_handler);
signal(SIGINT, sigint_handler); |
... then set up pty and ttySx to send SIGIOs to this process...
and now the important bit:
| Code: | sigset_t waitmask;
sigemptyset(&waitmask);
sigaddset(&waitmask, SIGIO);
// sigaddset(&waitmask, SIGTERM);
// sigaddset(&waitmask, SIGINT);
while(1){
sigsuspend(&waitmask); // pause as long as no signals or interrupts appear
} // use SIGINT or SIGTERM to properly shutdown programme |
other functions etc...
What strikes me, is that, although setting up the signal handlers it did not react at all, when I had pause() instead of sigsuspend() in the endless-loop.
Furthermore I can only shut down the programme with ctrl-c when "waitmask" is set exactly as above, although the SIGTERM and SIGINT are those signals, which I've implemented for that purpose. Does the programme think that I've sent it a SIGIO when I enter ctrl-c?
I'd be glad if anyone could answer my questions and give some explanations as to why those strange(?) things happen.
My environment: glibc 2.3.2-r1, anjuta (but testing done outside of anjuta because of the silly gnome-pty-helper, which blocks those crucial signals), xterm
Cheers, geta
Last edited by geta on Thu Sep 18, 2003 11:10 am; edited 1 time in total |
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puggy
Bodhisattva
Joined: 28 Feb 2003
Posts: 1992
Location: Oxford, UK
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| Posted: Wed Sep 17, 2003 10:03 pm Post subject: |
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Request for programming help so... Moving to Portage & Programming from Off The Wall.
Puggy
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