freebsd man page for sigprocmask

SIGPROCMASK(2)						      BSD System Calls Manual						    SIGPROCMASK(2)

NAME
     sigprocmask -- manipulate current signal mask

LIBRARY
     Standard C Library (libc, -lc)

SYNOPSIS
     #include <signal.h>

     int
     sigprocmask(int how, const sigset_t * restrict set, sigset_t * restrict oset);

DESCRIPTION
     The sigprocmask() system call examines and/or changes the current signal mask (those signals that are blocked from delivery).  Signals are
     blocked if they are members of the current signal mask set.

     If set is not null, the action of sigprocmask() depends on the value of the how argument.	The signal mask is changed as a function of the
     specified set and the current mask.  The function is specified by how using one of the following values from <signal.h>:

     SIG_BLOCK	  The new mask is the union of the current mask and the specified set.

     SIG_UNBLOCK  The new mask is the intersection of the current mask and the complement of the specified set.

     SIG_SETMASK  The current mask is replaced by the specified set.

     If oset is not null, it is set to the previous value of the signal mask.  When set is null, the value of how is insignificant and the mask
     remains unset providing a way to examine the signal mask without modification.

     The system quietly disallows SIGKILL or SIGSTOP to be blocked.

     In threaded applications, pthread_sigmask(3) must be used instead of sigprocmask().

RETURN VALUES
     The sigprocmask() function returns the value 0 if successful; otherwise the value -1 is returned and the global variable errno is set to
     indicate the error.

ERRORS
     The sigprocmask() system call will fail and the signal mask will be unchanged if one of the following occurs:

     [EINVAL]		The how argument has a value other than those listed here.

SEE ALSO
     kill(2), sigaction(2), sigpending(2), sigsuspend(2), fpsetmask(3), pthread_sigmask(3), sigsetops(3)

STANDARDS
     The sigprocmask() system call is expected to conform to ISO/IEC 9945-1:1990 (``POSIX.1'').

BSD
								    May 7, 2010 							       BSD