SETJMP(3) BSD Programmer's Manual SETJMP(3)
sigsetjmp, siglongjmp, setjmp, longjmp, _setjmp, _longjmp, longjmperror -
non-local jumps
#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);
The sigsetjmp(), setjmp(), and _setjmp() functions save their calling en-
vironment 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 invo-
cation 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 invo-
cation 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() function saves the signal mask if the argument savemask
is non-zero, and the siglongjmp() function restores the signal mask if it
was saved by such call. 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 porta-
bility.
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().
sigaction(2), sigaltstack(2), signal(3)
The setjmp() and longjmp() functions conform to ANSI X3.159-1989 ("ANSI
C89"). The sigsetjmp() and siglongjmp() functions conform to IEEE Std
1003.1-1990 ("POSIX.1").
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.
MirBSD #10-current March 31, 2012 1