(libc.info.gz) Handler Returns

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(libc.info.gz) Defining Handlers

(libc.info.gz) Termination in Handler

 
 24.4.1 Signal Handlers that Return
 ----------------------------------
 
 Handlers which return normally are usually used for signals such as
 'SIGALRM' and the I/O and interprocess communication signals.  But a
 handler for 'SIGINT' might also return normally after setting a flag
 that tells the program to exit at a convenient time.
 
    It is not safe to return normally from the handler for a program
 error signal, because the behavior of the program when the handler
 function returns is not defined after a program error.   Program
 Error Signals.
 
    Handlers that return normally must modify some global variable in
 order to have any effect.  Typically, the variable is one that is
 examined periodically by the program during normal operation.  Its data
 type should be 'sig_atomic_t' for reasons described in  Atomic Data
 Access.
 
    Here is a simple example of such a program.  It executes the body of
 the loop until it has noticed that a 'SIGALRM' signal has arrived.  This
 technique is useful because it allows the iteration in progress when the
 signal arrives to complete before the loop exits.
 
 
      #include <signal.h>
      #include <stdio.h>
      #include <stdlib.h>
 
      /* This flag controls termination of the main loop. */
      volatile sig_atomic_t keep_going = 1;
 
      /* The signal handler just clears the flag and re-enables itself. */
      void
      catch_alarm (int sig)
      {
        keep_going = 0;
        signal (sig, catch_alarm);
      }
 
      void
      do_stuff (void)
      {
        puts ("Doing stuff while waiting for alarm....");
      }
 
      int
      main (void)
      {
        /* Establish a handler for SIGALRM signals. */
        signal (SIGALRM, catch_alarm);
 
        /* Set an alarm to go off in a little while. */
        alarm (2);
 
        /* Check the flag once in a while to see when to quit. */
        while (keep_going)
          do_stuff ();
 
        return EXIT_SUCCESS;
      }
 

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(libc.info.gz) Defining Handlers

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