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LIBUNWIND-SETJMP(3)          Programming Library           LIBUNWIND-SETJMP(3)


NAME

       libunwind-setjmp -- libunwind-based non-local gotos


SYNOPSIS

       #include <setjmp.h>

       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);


DESCRIPTION

       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().


CAVEATS

       *      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
              information).

       *      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().


FILES

       -lunwind-setjmp
               The library an application should be linked against to ensure
              it uses the libunwind-based non-local goto routines.


SEE ALSO

       libunwind(3), setjmp(3), longjmp(3), _setjmp(3), _longjmp(3),
       sigsetjmp(3), siglongjmp(3)


AUTHOR

       David Mosberger-Tang
       Email: dmosberger@gmail.com
       WWW: http://www.nongnu.org/libunwind/.

Programming Library             16 August 2007             LIBUNWIND-SETJMP(3)

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