'\" te
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.TH SIGPROCMASK 2 "Nov 24, 2014"
.SH NAME
sigprocmask \- change or examine caller's signal mask
.SH SYNOPSIS
.LP
.nf
#include <signal.h>

\fBint\fR \fBsigprocmask\fR(\fBint\fR \fIhow\fR, \fBconst sigset_t *restrict\fR \fIset\fR,
     \fBsigset_t *restrict\fR \fIoset\fR);
.fi

.SH DESCRIPTION
.LP
The \fBsigprocmask()\fR function is used to examine and/or change the caller's
signal mask. If the value of the \fIhow\fR argument is \fBSIG_BLOCK\fR, the set
pointed to by the \fIset\fR argument is added to the current signal mask. If
the value of the \fIhow\fR argument is \fBSIG_UNBLOCK\fR, the set pointed by
the \fIset\fR argument is removed from the current signal mask. If the value of
the \fIhow\fR argument is \fBSIG_SETMASK\fR, the current signal mask is
replaced by the set pointed to by the \fIset\fR argument. If the \fIoset\fR
argument is not \fINULL\fR, the previous mask is stored in the space pointed to
by \fIoset\fR. If the value of the  \fIset\fR argument is \fINULL\fR, the value
\fIhow\fR is not significant and the caller's signal mask is unchanged; thus,
the call can be used to inquire about currently blocked signals. If the
\fIset\fR or \fIoset\fR argument points to an invalid address, the behavior is
undefined and \fBerrno\fR may be set to \fBEFAULT\fR.
.sp
.LP
If there are any pending unblocked signals after the call to
\fBsigprocmask()\fR, at least one of those signals will be delivered before the
call to \fBsigprocmask()\fR returns.
.sp
.LP
It is not possible to block signals that cannot be caught or ignored (see
\fBsigaction\fR(2)). It is also not possible to block or unblock SIGCANCEL, as
SIGCANCEL is reserved for the implementation of POSIX thread cancellation (see
\fBpthread_cancel\fR(3C) and \fBcancellation\fR(7)). This restriction is
silently enforced by the standard C library.
.sp
.LP
If \fBsigprocmask()\fR fails, the caller's signal mask is not changed.
.SH RETURN VALUES
.LP
Upon successful completion, \fB0\fR is returned. Otherwise, \fB\(mi1\fR is
returned and \fBerrno\fR is set to indicate the error.
.SH ERRORS
.LP
The \fBsigprocmask()\fR function will fail if:
.sp
.ne 2
.na
\fB\fBEINVAL\fR\fR
.ad
.RS 10n
The value of the \fIhow\fR argument is not equal to one of the defined values.
.RE

.sp
.LP
The \fBsigprocmask()\fR function may fail if:
.sp
.ne 2
.na
\fB\fBEFAULT\fR\fR
.ad
.RS 10n
The \fIset\fR or \fIoset\fR argument points to an illegal address.
.RE

.SH ATTRIBUTES
.LP
See \fBattributes\fR(7) for descriptions of the following attributes:
.sp

.sp
.TS
box;
c | c
l | l .
ATTRIBUTE TYPE	ATTRIBUTE VALUE
_
Interface Stability	Standard
_
MT-Level	Async-Signal-Safe
.TE

.SH SEE ALSO
.LP
.BR sigaction (2),
.BR pthread_cancel (3C),
.BR pthread_sigmask (3C),
.BR signal (3C),
.BR sigsetops (3C),
.BR signal.h (3HEAD),
.BR attributes (7),
.BR cancellation (7)
.SH NOTES
.LP
The call to \fBsigprocmask()\fR affects only the calling thread's signal mask.
It is identical to a call to \fBpthread_sigmask\fR(3C).
.sp
.LP
Signals that are generated synchronously should not be masked. If such a signal
is blocked and delivered, the receiving process is killed.