The distinction between setjmp()/ longjmp() and
sigsetjmp()/ siglongjmp() is only significant for programs which
use sigaction(), sigprocmask(), or sigsuspend().
Note that since this function is defined in terms of setjmp(), if
savemask is zero, it is unspecified whether the signal mask is saved.
The ISO C standard specifies various restrictions on the usage of the
setjmp() macro in order to permit implementors to recognize the name in
the compiler and not implement an actual function. These same restrictions
apply to the sigsetjmp() macro.
There are processors that cannot easily support these calls, but this was not
considered a sufficient reason to exclude them.
4.2 BSD, 4.3 BSD, and XSI-conformant systems provide functions named
_setjmp() and _longjmp() that, together with setjmp() and
longjmp(), provide the same functionality as sigsetjmp() and
siglongjmp(). On those systems, setjmp() and longjmp()
save and restore signal masks, while _setjmp() and _longjmp() do
not. On System V Release 3 and in corresponding issues of the SVID,
setjmp() and longjmp() are explicitly defined not to save and
restore signal masks. In order to permit existing practice in both cases, the
relation of setjmp() and longjmp() to signal masks is not
specified, and a new set of functions is defined instead.
The longjmp() and siglongjmp() functions operate as in the
previous issue provided the matching setjmp() or sigsetjmp() has
been performed in the same thread. Non-local jumps into contexts saved by
other threads would be at best a questionable practice and were not considered
worthy of standardization.
Portions of this text are reprinted and reproduced in electronic form from IEEE
Std 1003.1, 2003 Edition, Standard for Information Technology -- Portable
Operating System Interface (POSIX), The Open Group Base Specifications Issue
6, Copyright (C) 2001-2003 by the Institute of Electrical and Electronics
Engineers, Inc and The Open Group. 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.opengroup.org/unix/online.html