DragonFly On-Line Manual Pages
LIBUNWIND-SETJMP(3) Programming Library LIBUNWIND-SETJMP(3)
libunwind-setjmp -- libunwind-based non-local gotos
int setjmp(jmp_buf env);
void longjmp(jmp_buf env, int val);
int _setjmp(jmp_buf env);
void _longjmp(jmp_buf env, int val);
int sigsetjmp(sigjmp_buf env, int savemask);
void siglongjmp(sigjmp_buf env, int val);
The unwind-setjmp library offers a libunwind-based implementation of
non-local gotos. This implementation is intended to be a drop-in
replacement for the normal, system-provided routines of the same name.
The main advantage of using the unwind-setjmp library is that setting
up a non-local goto via one of the setjmp() routines is very fast.
Typically, just 2 or 3 words need to be saved in the jump-buffer (plus
one call to sigprocmask(2), in the case of sigsetjmp). On the other
hand, executing a non-local goto by calling one of the longjmp()
routines tends to be much slower than with the system-provided
routines. In fact, the time spent on a longjmp() will be proportional
to the number of call frames that exist between the points where
setjmp() and longjmp() were called. For this reason, the unwind-setjmp
library is beneficial primarily in applications that frequently call
setjmp() but only rarely call longjmp().
* The correct operation of this library depends on the presence of
correct unwind information. On newer platforms, this is rarely
an issue. On older platforms, care needs to be taken to ensure
that each of the functions whose stack frames may have to be
unwound during a longjmp() have correct unwind information (on
those platforms, there is usually a compiler-switch, such as
-funwind-tables, to request the generation of unwind
* The contents of jmp_buf and sigjmp_buf as setup and used by
these routines is completely different from the ones used by the
system-provided routines. Thus, a jump-buffer created by the
libunwind-based setjmp()/_setjmp may only be used in a call to
the libunwind-based longjmp()/_longjmp(). The analogous applies
for sigjmp_buf with sigsetjmp() and siglongjmp().
The library an application should be linked against to ensure
it uses the libunwind-based non-local goto routines.
libunwind(3), setjmp(3), longjmp(3), _setjmp(3), _longjmp(3),
Programming Library 16 August 2007 LIBUNWIND-SETJMP(3)