SETJMP(3) OpenBSD Programmer's Manual SETJMP(3)NAME
sigsetjmp, siglongjmp, setjmp, longjmp, _setjmp, _longjmp, longjmperror -
non-local jumps
SYNOPSIS
#include <setjmp.h>
int
sigsetjmp(sigjmp_buf env, int savemask);
void
siglongjmp(sigjmp_buf env, int val);
int
setjmp(jmp_buf env);
void
longjmp(jmp_buf env, int val);
int
_setjmp(jmp_buf env);
void
_longjmp(jmp_buf env, int val);
void
longjmperror(void);
DESCRIPTION
The sigsetjmp(), setjmp(), and _setjmp() functions save their calling
environment in env. Each of these functions returns 0.
The corresponding longjmp() functions restore the environment saved by
the most recent invocation of the respective setjmp() function. They
then return so that program execution continues as if the corresponding
invocation of the setjmp() call had just returned the value specified by
val, instead of 0. The value specified by val must be non-zero; a 0
value is treated as 1 to allow the programmer to differentiate between a
direct invocation of setjmp() and a return via longjmp().
Pairs of calls may be intermixed; i.e., both sigsetjmp() and siglongjmp()
as well as setjmp() and longjmp() combinations may be used in the same
program. However, individual calls may not -- e.g., the env argument to
setjmp() may not be passed to siglongjmp().
The longjmp() routines may not be called after the routine which called
the setjmp() routines returns.
All accessible objects have values as of the time the longjmp() routine
was called, except that the values of objects of automatic storage
invocation duration that do not have the volatile type and have been
changed between the setjmp() invocation and longjmp() call are
indeterminate.
The setjmp()/longjmp() function pairs save and restore the signal mask
while the _setjmp()/_longjmp() function pairs save and restore only the
register set and the stack (see sigmask(3)).
The sigsetjmp()/siglongjmp() function pairs save and restore the signal
mask if the argument savemask is non-zero. Otherwise, only the register
set and the stack are saved.
In other words, setjmp()/longjmp() are functionally equivalent to
sigsetjmp()/siglongjmp() when sigsetjmp() is called with a non-zero
savemask argument. Conversely, _setjmp()/_longjmp() are functionally
equivalent to sigsetjmp()/siglongjmp() when sigsetjmp() is called with a
zero-value savemask.
The sigsetjmp()/siglongjmp() interfaces are preferred for maximum
portability.
ERRORS
If the contents of the env are corrupted or correspond to an environment
that has already returned, the longjmp() routine calls the routine
longjmperror(3). If longjmperror() returns, the program is aborted (see
abort(3)). The default version of longjmperror() prints the message
``longjmp botch'' to standard error and returns. User programs wishing
to exit more gracefully should write their own versions of
longjmperror().
SEE ALSOsigaction(2), sigaltstack(2), signal(3)STANDARDS
The setjmp() and longjmp() functions conform to ANSI X3.159-1989 (``ANSI
C''). The sigsetjmp() and siglongjmp() functions conform to IEEE Std
1003.1-1990 (``POSIX'').
CAVEATS
Historically, on AT&T System V UNIX, the setjmp()/longjmp() functions
have been equivalent to the BSD _setjmp()/_longjmp() functions and do not
restore the signal mask. Because of this discrepancy, the
sigsetjmp()/siglongjmp() interfaces should be used if portability is
desired.
Use of longjmp() or siglongjmp() from inside a signal handler is not as
easy as it might seem. Generally speaking, all possible code paths
between the setjmp() and longjmp() must be signal race safe, as discussed
in signal(3). Furthermore, the code paths must not do resource
management (such as open(2) or close(2)) without blocking the signal in
question, or resources might be mismanaged. Obviously this makes
longjmp() much less useful than previously thought.
OpenBSD 4.9 May 31, 2007 OpenBSD 4.9