This manual page is part of the POSIX Programmer's Manual. The Linux
implementation of this interface may differ (consult the
corresponding Linux manual page for details of Linux behavior), or
the interface may not be implemented on Linux.
The implementation of the sigemptyset() (or sigfillset()) function
could quite trivially clear (or set) all the bits in the signal set.
Alternatively, it would be reasonable to initialize part of the
structure, such as a version field, to permit binary-compatibility
between releases where the size of the set varies. For such reasons,
either sigemptyset() or sigfillset() must be called prior to any
other use of the signal set, even if such use is read-only (for
example, as an argument to sigpending()). This function is not
intended for dynamic allocation.
The sigfillset() and sigemptyset() functions require that the
resulting signal set include (or exclude) all the signals defined in
this volume of POSIX.1‐2008. Although it is outside the scope of this
volume of POSIX.1‐2008 to place this requirement on signals that are
implemented as extensions, it is recommended that implementation-
defined signals also be affected by these functions. However, there
may be a good reason for a particular signal not to be affected. For
example, blocking or ignoring an implementation-defined signal may
have undesirable side-effects, whereas the default action for that
signal is harmless. In such a case, it would be preferable for such a
signal to be excluded from the signal set returned by sigfillset().
In early proposals there was no distinction between invalid and
unsupported signals (the names of optional signals that were not
supported by an implementation were not defined by that
implementation). The [EINVAL] error was thus specified as a required
error for invalid signals. With that distinction, it is not necessary
to require implementations of these functions to determine whether an
optional signal is actually supported, as that could have a
significant performance impact for little value. The error could have
been required for invalid signals and optional for unsupported
signals, but this seemed unnecessarily complex. Thus, the error is
optional in both cases.
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2013 Edition, Standard for Information
Technology -- Portable Operating System Interface (POSIX), The Open
Group Base Specifications Issue 7, Copyright (C) 2013 by the
Institute of Electrical and Electronics Engineers, Inc and The Open
Group. (This is POSIX.1-2008 with the 2013 Technical Corrigendum 1
applied.) In the event of any discrepancy between this version and
the original IEEE and The Open Group Standard, the original IEEE and
The Open Group Standard is the referee document. The original
Standard can be obtained online at http://www.unix.org/online.html .
Any typographical or formatting errors that appear in this page are
most likely to have been introduced during the conversion of the
source files to man page format. To report such errors, see
IEEE/The Open Group 2013 SIGEMPTYSET(3P)