sigblock

Purpose

     Blocks signals.

Syntax

     int sigblock (mask)
     int mask;

Description

     The sigblock system call  causes the signals specified by
     the mask parameter to be added to the set of signals cur-
     rently  being blocked  from  delivery.   The signals  are
     blocked from delivery by logically OR-ing the mask param-
     eter into the process's signal mask.  Signal i is blocked
     if the i-th bit in mask is a 1.

     &c2del.  It  is not  possible to block  SIGKILL.  &c2off.
     &c2ins.  It is  not possible to block  SIGKILL or SIGSAK.
     &c2off.   The  system  provides  no  indication  of  this
     restriction.

     Typically,  the sigblock  system  call is  used to  block
     signals  during  a critical  section  of  code, and  then
     sigsetmask is called to restore  the mask to the previous
     value returned by sigblock.

Return Value

     Upon completion,  the previous  set of masked  signals is
     returned.

Example

     The  following  example sets  the  signal  mask to  block
     SIGINT from delivery, in addition to the signals that are
     already blocked:

       #include <signal.h>

       int prevmask;
        . . .
       prevmask = sigblock (1 << (SIGINT - 1));

Related Information

     In   this   book:    "kill,"  "signal,"   "sigvec,"   and
     "sigsetmask."