change or examine signal mask
int sigprocmask(int how, const sigset_t *set, sigset_t *oset);
The sigprocmask function is used to examine and/or change the
calling process's signal mask.
If the value how is SIG_BLOCK,
the set pointed to by the argument set is added to the
current signal mask.
If the value how is SIG_UNBLOCK, the set pointed
by the argument set is removed from the current signal mask.
If the value how is SIG_SETMASK, the current signal mask is
replaced by the set pointed to by the argument set.
If the argument oset
is not NULL, the previous mask is stored in the space pointed to by
If the value of the argument set is NULL,
the value how is not significant
and the process's signal mask is unchanged; thus, the call can be used
to enquire about currently blocked signals.
If there are any pending unblocked signals after the call to sigprocmask,
at least one of those signals will be delivered before the call to
It is not possible to block those signals that cannot be ignored
This restriction is silently imposed by the system.
If sigprocmask fails, the process's signal
mask is not changed.
On success, sigprocmask returns 0.
On failure, sigprocmask returns -1 and sets errno to identify the error.
In the following conditions, sigprocmask fails and sets errno to:
The value of the how argument is not equal to one of the defined values.
The value of set or oset points outside the process's allocated
Considerations for threads programming
Signal masks are maintained per thread.
for further details.
Considerations for lightweight processes
Signal masks are internally maintained per LWP.
The Threads Library has a wrapper function for this system call
to make its effect per thread.
© 2004 The SCO Group, Inc. All rights reserved.
UnixWare 7 Release 7.1.4 - 25 April 2004