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manipulate current signal mask

#include <signal.h>
sigprocmask(int how, const sigset_t *set, sigset_t *oset);

The sigprocmask() function 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 parameter how, which can be one of the following values:
The new mask is the union of the current mask and the specified set.
The new mask is the intersection of the current mask and the complement of the specified set.
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 unchanged, providing a way to examine the signal mask without modification.
The system quietly disallows SIGKILL or SIGSTOP to be blocked.

Upon successful completion, the value 0 is returned; otherwise the value -1 is returned and the global variable errno is set to indicate the error.

The sigprocmask() call will fail and the signal mask will be unchanged if one of the following occurs:
how has a value other than those listed here.

kill(2), sigaction(2), sigsuspend(2), sigsetops(3)

The sigprocmask() function call is expected to conform to IEEE Std 1003.1-2008 (“POSIX.1”).
December 14, 2014 OpenBSD-5.8