sigaction(3-thr)                                           sigaction(3-thr)

NAME
     sigaction - examines and changes synchronous signal actions (POSIX
     software signal facilities)

SYNOPSIS
     #include <signal.h>

     struct sigaction {
         void (*sahandler)();
         sigsett samask;
         int saflags;
     };

     int sigaction(int sig; const struct sigaction *act;
                   struct sigaction *oact);

PARAMETERS
     sig       Synchronous signal to examine or change.

     act       Points to a sigaction structure that describes the action to
               be taken upon receipt of the signal indicated by the value
               of the act parameter.

     oact      Points to a sigaction structure in which the signal action
               data in effect at the time of the sigaction() function call
               is returned.

DESCRIPTION
     The sigaction POSIX service allows for per-thread handlers to be
     installed for catching synchronous signals. It is called in a mul-
     tithreaded process to establish thread specific actions for such sig-
     nals. This call is the POSIX equivalent of the sigaction() system call
     with the following exceptions or modifications:

     -  The sigaction() routine only modifies behavior for individual
        threads.

     -  The sigaction() routine only works for synchronous signals.
        Attempting to set a signal action for an asynchronous signal is an
        error. This is true even in a single-threaded process.

        Any multithreaded application using DCE Threads will need to use
        the sigwait() function for dealing with asynchronous signals. The
        sigwait() function can be used to synchronously wait for delivery
        of asynchronously generated signals.

     -  The SARESTART flag is always set by the underlying system in POSIX
        mode so that interrupted system calls will fail with return value
        of -1 and the EINTR error in errno instead of getting restarted.






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sigaction(3-thr)                                           sigaction(3-thr)

        The system's SARESTART flag has the opposite meaning of the
        SARESTART flag in the saflags field and is always set in the
        underlying system call resulting from sigaction() regardless of
        whether SARESTART was indicated in saflags.

     -  The signal mask is manipulated using the POSIX sigsetops(3C) func-
        tions. They are sigemptyset(3C), sigfillset(3C), sigaddset(3C),
        sigdelset(3C), and sigismember(3C).

     The sigaction() function can be used to inquire about the current han-
     dling of a given signal by specifying a null pointer for act, since
     the action is unchanged unless this parameter is not a null pointer.
     In order for the signal action in effect at the time of the
     sigaction() call to be returned, the oact parameter must not be a null
     pointer.

RETURN VALUES
     Possible return values are as follows:

     EFAULT    Either act or oact points to memory which is not a valid
               part of the process address space. A new signal handler is
               not installed.

     EINVAL    The value specified by sig is invalid. A new signal handler
               is not installed.

     EINVAL    An attempt is made to ignore or supply a handler for SIGKILL
               or SIGSTOP. A new signal handler is not installed.

SEE ALSO
     sigsuspend(2), sigvec(2), siginterrupt(3), sigpending(3-thr),
     sigprocmask(3-thr), setjmp(3C), sigsetops(3C), signal(5), tty(7).






















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