signal interrupts reading from queue

aral · 10-09-2006, 01:29 PM

I have a process who's main thread reads messages from a SystemV message queue every 5 seconds (because the messages arive in the queue every 5 seconds ) . Between two readings from the queue the main thread is blocked in a read( msgrcv call) from the queue , because there are no messages in the queue for 5 seconds. This process is supposed to be stoped by a signal sent from another process . So it should exit the reading loop when the signal arrives, destroy all resources and end properly. But the signal ,which is caught by the signal handler I installed ( this handler only changes a flag ), interrupts the read (msgrcv call) from the queue so the program stops failing at the msgrcv call and thus it doesn't have time to destroy resources and end properly. How could I fix this? I want the process which catches the signal to end properly, and destroy all resources .. How can I do this ?

Hko · 10-10-2006, 10:57 AM

Quote:

Originally Posted by aral

But the signal ,which is caught by the signal handler I installed ( this handler only changes a flag ), interrupts the read (msgrcv call) from the queue so the program stops failing at the msgrcv call and thus it doesn't have time to destroy resources and end properly. How could I fix this? I want the process which catches the signal to end properly, and destroy all resources .. How can I do this ?

I suggest trying something like this:

Code:

/* Other #include's */

#include <errno.h>

/* ... */

int result;

/* ... */

result = msgrcv( ... );
if (result == -1) {
    if (errno == EINTR) {  /* msgrcv() was interrupted by a signal */
        if (flag_set_in_signal_handler) {
            your_resources_cleanup();
            exit(0);
        }
        exit(1);
     }

     /* Other error-handling / printing / logging */
}

/* msgrcv() was successful. 
 * Do somthing with the message just fetched */

Hope this helps.

chrism01 · 10-10-2006, 08:24 PM

I solved a similar issue in Perl ie blocking listen plus clean exit.
Waht I did was make the sighandler close (actually shutdown) the listen socket. this causes the listen loop to then continue and check for an exit/cleanup flag.
HTH
Actually, this was multi-threaded, but I think(?) the same trick would work in single thr.