berk_signal(3C)                   SDK R4.11                  berk_signal(3C)


NAME
       berksignal, signal - simplified software signal facilities

SYNOPSIS
       #define BSDSIGNALFLAVOR
       #include <signal.h>

       (*signal(sig, func))()
                int (*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/UX (Trademark) 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 termio(7)).  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 occurrences 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 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.

   Considerations for Threads Programming
                    +------------+-----------------------------+
                    |            |                      async- |
                    |function    | reentrant   cancel   cancel |
                    |            |             point     safe  |
                    +------------+-----------------------------+
                    |berksignal |     Y         N        N    |
                    |signal      |     Y         N        N    |
                    +------------+-----------------------------+
RETURN VALUE
       The previous action is returned on a successful call.  Otherwise, -1
       is returned and errno is set to indicate the error.

DIAGNOSTICS
       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), reentrant(3), setjmp(3C),
       termio(7)

NOTES
       signal(3C) provides compatibility with BSD signal handling while
       signal(2) is System V based.  You can use signal(3C) 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
            berksignal, which is signal(3C).  signal(2) is unavailable with
            this method.

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

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


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