SIGPROCMASK(2)                       BSD                        SIGPROCMASK(2)



NAME
     sigprocmask - Set the current signal mask

SYNOPSIS
     #include <signal.h>

     int sigprocmask (how, set, o_set)
     int how;
     const sigset_t *set;
     sigset_t *o_set;


DESCRIPTION
     The sigprocmask function is used to examine or change the signal mask of
     the calling process. The arguments are defined as follows:

     how  Indicates the manner in which the set of masked signals is changed;
          it has one of the following values:

          SIG_BLOCK
               The resulting set is the union of the current set and the
               signal set pointed to by the set argument.

          SIG_UNBLOCK
               The resulting set is the intersection of the current set and
               the complement of the signal set pointed to by the set
               argument.

          SIG_SETMASK
               The resulting set is the signal set pointed to by the set
               argument.

     set  Specifies the signal set.  If the value of the set argument is not
          null, it points to a set of signals to be used to change the
          currently blocked set. If the value of the set argument is null, the
          value of the how argument is not significant and the process signal
          mask is unchanged; thus, the call can be used to inquire about
          currently blocked signals.

     o_set
          If the o_set argument is not the null value, the signal mask in
          effect at the time of the call is stored in the spaced pointed to by
          the o_set argument.

     If there are any pending unblocked signals after the call to sigprocmask,
     at least one of those signals will be delivered before the call to
     sigprocmask returns.

     It is not possible to block those signals which cannot be ignored. That
     is enforced by the system without causing an error to be indicated.

     If any of the SIGFPE, SIGILL or SIGSEGV signals are generated while they
     are blocked, the result is undefined, unless the signal was generated by
     a call to the kill(2) function.

     If the sigprocmask function fails, the process' signal mask is not
     changed.

     Applications should call either sigemptyset(3) or sigfillset(3) at least
     once for each object of type sigset_t prior to any other use of that
     object.  If such an object is not initialized in this way, but is

     nonetheless supplied as an argument to the sigprocmask function, the
     results are undefined.

EXAMPLE
     To set the signal mask to block only the SIGINT signal from delivery,
     enter:

          #include <signal.h>

          int return_value;
          sigset_t newset;
          sigset_t *newset_p;
           . . .
          newset_p = &newset;
          sigemptyset(newset_p);
          sigaddset(newset_p, SIGINT);
          return_value = sigprocmask (SIG_SETMASK, newset_p, NULL);

DIAGNOSTICS
     Upon successful completion, the sigprocmask function returns a value of 0
     (zero). Otherwise, a value of -1 is returned.

ERRORS
     If the sigprocmask() function fails, errno will be set to one of the
     following values:

     [EINVAL]  The value of the how argument is not equal to one of the
               defined values.

SEE ALSO
     kill(2), sigaction(2), sigpause(2), sigsuspend(2), sigsetops(3),