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The
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 is not null, the action of depends
on the value of the parameter The signal mask is changed as a function
of the specified and the current mask. The function is specified by using
one of the following values from The new mask is the union of the current
mask and the specified The new mask is the intersection of the current
mask and the complement of the specified The current mask is replaced
by the specified If is not null, it is set to the previous value of
the signal mask. When is null, the value of is insignificant and the mask
remains unset providing a way to examine the signal mask without modification.
The system quietly disallows or to be blocked.
A 0 value
indicated that the call succeeded. A -1 return value indicates an error
occurred and is set to indicated the reason.
The call will fail
and the signal mask will be unchanged if one of the following occurs:
has a value other than those listed here.
The function
call is expected to conform to
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