manipulate current signal mask
() 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.
is not null, the action of
() depends on the value of the
, which can be one of the
- The new mask is the union of the current mask and the
- 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
is not null, it is set to the previous
value of the signal mask. When set
the value of how
is insignificant and the
mask remains unchanged, providing a way to examine the signal mask without
The system quietly disallows
to be blocked.
Upon successful completion, the value 0 is returned; otherwise the
value -1 is returned and the global variable
is set to indicate the error.
() 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.
() function call is expected to
conform to IEEE Std 1003.1-2008