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     sigprocmask — manipulate current signal mask


     Standard C Library (libc, -lc)


     #include <signal.h>

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


     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().


     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.


     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.


     kill(2), sigaction(2), sigpending(2), sigsuspend(2), fpsetmask(3), pthread_sigmask(3),


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