berk_signal(3)             DG/UX 4.30              berk_signal(3)



     NAME
          berk_signal, signal - simplified software signal facilities

     SYNOPSIS
          #define _BSD_SIGNAL_FLAVOR
          #include <signal.h>

          (*signal(sig, func))()
                   void (*func)();

     DESCRIPTION
          Signal is a simplified interface to the more general
          sigvec(2) facility.  If you define the _BSD_SIGNAL_FLAVOR
          macro or only the _BSD_SOURCE macro when you compile your C
          application, you will get the signal functionality described
          in this entry; otherwise, you will get the functionality
          described in signal(2).  For more information on the
          _BSD_SIGNAL_FLAVOR and _BSD_SOURCE macros, see Porting
          Applications to the DG/UXTM System.

          A signal is generated by some abnormal event, initiated by a
          user at a terminal (quit, interrupt, stop), by a program
          error (bus error, etc.), by request of another program
          (kill), or when a process is stopped because it wishes to
          access its control terminal while in the background (see
          tty(4)).  Signals are optionally generated when a process
          resumes after being stopped, when the status of child
          processes changes, or when input is ready at the control
          terminal.  Most signals cause termination of the receiving
          process if no action is taken; some signals instead cause
          the process receiving them to be stopped, or are simply
          discarded if the process has not requested otherwise.
          Except for the SIGKILL and SIGSTOP signals, the signal call
          allows signals either to be ignored or to cause an interrupt
          to a specified location.  For a list of the signals, see
          <sys/signal.h>.

          If func is SIG_DFL, the default action for signal sig is
          reinstated.  If func is SIG_IGN, the signal is subsequently
          ignored and pending instances of the signal are discarded.
          Otherwise, when the signal occurs, further occurences of the
          signal are automatically blocked and func is called.

          A return from the function unblocks the handled signal and
          continues the process at the point it was interrupted.
          Unlike previous signal facilities, the handler func remains
          installed after a signal has been delivered.

          If a caught signal occurs during certain system calls,
          causing the call to terminate prematurely, the call is
          automatically restarted.  In particular this can occur
          during a read(2) or write(2) on a slow device (such as a



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     berk_signal(3)             DG/UX 4.30              berk_signal(3)



          terminal; but not a file) and during a wait(2).

          The value of signal is the previous (or initial) value of
          func for the particular signal.

          After a fork(2) or vfork(2) the child inherits all signals.
          Execve(2) resets all caught signals to the default action;
          ignored signals remain ignored.

     RETURN VALUE
          The previous action is returned on a successful call.
          Otherwise, -1 is returned and errno is set to indicate the
          error.

     ERRORS
          Signal will fail and no action will take place if one of the
          following occur:

          EINVAL         Sig is not a valid signal number.

          EINVAL         An attempt is made to ignore or supply a
                         handler for SIGKILL or SIGSTOP.

          EINVAL         An attempt is made to ignore SIGCONT (by
                         default SIGCONT is ignored).

     SEE ALSO
          kill(1), ptrace(2), kill(2), sigvec(2), sigblock(2),
          signal(2), sigsetmask(2), sigpause(2), sigstack(2),
          setjmp(3), tty(4)

     NOTES
          Signal(3) provides compatibility with BSD signal handling
          while signal(2) is System V based.  You can use signal(3) in
          either of the following ways:

          1)   Define _BSD_SIGNAL_FLAVOR (or define _BSD_SOURCE while
               not defining _POSIX_SOURCE or _SYSV3_SOURCE), include
               <signal.h>, and call signal().  Calls to signal will
               translate to berk_signal, which is signal(3).
               signal(2) is unavailable with this method.

          2)   Include <signal.h> and call berk_signal.  With this
               method you can use both System V signal facilities
               (call signal to get signal(2)) and BSD signal
               facilities (call berk_signal to get signal(3)).

     STANDARDS
          When using m88kbcs as the Software Development Environment
          (SDE) target, the berk_signal function will be an incomplete
          emulation of Berkeley semantics.  Since we are using BCS
          system calls, system call restart is not available.



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     berk_signal(3)             DG/UX 4.30              berk_signal(3)



          Instead, interrupted system calls will fail with errno set
          to EINTR.  Also, since this is an emulation requiring
          several BCS system calls, a slight performance degradation
          may be noticed in comparison to using berk_signal in
          /lib/libc.a.


















































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