rt_sigprocmask

       #include <signal.h>

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

   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

       sigprocmask(): _POSIX_C_SOURCE >= 1 || _XOPEN_SOURCE || _POSIX_SOURCE

DESCRIPTION
       sigprocmask()  is  used  to  fetch and/or change the signal mask of the
       calling thread.  The signal mask is the set of signals  whose  delivery
       is  currently  blocked  for  the  caller  (see  also signal(7) for more
       details).

       The behavior of the call is dependent on the value of how, as follows.

       SIG_BLOCK
              The set of blocked signals is the union of the current  set  and
              the set argument.

       SIG_UNBLOCK
              The  signals  in set are removed from the current set of blocked
              signals.  It is permissible to attempt to unblock a signal which
              is not blocked.

       SIG_SETMASK
              The set of blocked signals is set to the argument set.

       If  oldset is non-NULL, the previous value of the signal mask is stored
       in oldset.

       If set is NULL, then  the  signal  mask  is  unchanged  (i.e.,  how  is
       ignored),  but  the  current  value  of the signal mask is nevertheless
       returned in oldset (if it is not NULL).

       The use of sigprocmask() is unspecified in a multithreaded process; see
       pthread_sigmask(3).

RETURN VALUE
       sigprocmask() returns 0 on success and -1 on error.  In the event of an
       error, errno is set to indicate the cause.

ERRORS
       EFAULT The set or oldset argument points outside  the  process's  allo-
              cated address space.

       EINVAL The value specified in how was invalid.

CONFORMING TO
       POSIX.1-2001, POSIX.1-2008.

NOTES
       It  is not possible to block SIGKILL or SIGSTOP.  Attempts to do so are
       silently ignored.

   C library/kernel differences
       The  glibc wrapper function for sigprocmask() silently ignores attempts
       to block the two real-time signals that are used internally by the NPTL
       threading implementation.  See nptl(7) for details.

       The  original Linux system call was named sigprocmask().  However, with
       the addition of real-time signals in Linux 2.2, the fixed-size,  32-bit
       sigset_t  type supported by that system call was no longer fit for pur-
       pose.  Consequently, a new system call, rt_sigprocmask(), was added  to
       support  an enlarged sigset_t type.  The new system call takes a fourth
       argument, size_t sigsetsize, which specifies the size in bytes  of  the
       signal  sets in set and oldset.  This argument is currently required to
       have the value sizeof(sigset_t) (or the  error  EINVAL  results).   The
       glibc  sigprocmask()  wrapper  function  hides  these  details from us,
       transparently calling rt_sigprocmask() when the kernel provides it.

SEE ALSO
       kill(2),  pause(2),  sigaction(2),  signal(2),  sigpending(2),  sigsus-
       pend(2), pthread_sigmask(3), sigqueue(3), sigsetops(3), signal(7)

COLOPHON
       This  page  is  part of release 4.04 of the Linux man-pages project.  A
       description of the project, information about reporting bugs,  and  the
       latest     version     of     this    page,    can    be    found    at
       http://www.kernel.org/doc/man-pages/.

Linux                             2015-07-23                    SIGPROCMASK(2)
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