Basic signal handling in C++

Question

This is a pretty basic scenario but I\'m not finding too many helpful resources. I have a C++ program running in Linux that does file processing. Reads lines, does various t

Answer 1

I'd recommend checking out this link which gives the details on registering a signal.

Unless I'm mistaken, one important thing to remember is that any function inside an object expects a referent parameter, which means non-static member functions can't be signal handlers. I believe you'll need to register it either to a static member function, or some kind of global function. From there, if you have a specific object function you want to take care of your update, you'll need a way to reference that object.

Answer 2

I would handle it just like you might handle it in C. I think it's perfectly fine to have a stand-alone signal handler function, since you'll just be posting to a semaphore or setting a variable or some such, which another thread or object can inspect to determine if it needs to re-read the settings.

#include <signal.h>
#include <stdio.h>

/* or you might use a semaphore to notify a waiting thread */
static volatile sig_atomic_t sig_caught = 0;

void handle_sighup(int signum) 
{
    /* in case we registered this handler for multiple signals */ 
    if (signum == SIGHUP) {
        sig_caught = 1;
    }
}

int main(int argc, char* argv[]) 
{
    /* you may also prefer sigaction() instead of signal() */
    signal(SIGHUP, handle_sighup);

    while(1) {
        if (sig_caught) {
            sig_caught = 0;
            printf("caught a SIGHUP.  I should re-read settings.\n");
        }
    }

    return 0;
}

You can test sending a SIGHUP by using kill -1 `pidof yourapp`.

Answer 3

You can define a Boost signal corresponding to the OS signal and tie the Boost signal to your slot to invoke the respective handler.

Answer 4

There are several possibilities; it would not necessarily be overkill to implement all of them:

• Respond to a specific signal, just like C does. C++ works the same way. See the documentation for signal().
• Trigger on the modification timestamp of some file changing, like the database if it is stored in a flat file.
• Trigger once per hour, or once per day (whatever makes sense).