longjmp(3) - NetBSD Manual Pages

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SETJMP(3)               NetBSD Library Functions Manual              SETJMP(3)


NAME

     sigsetjmp, siglongjmp, setjmp, longjmp, _setjmp, _longjmp, longjmperror
     -- non-local jumps


LIBRARY

     Standard C Library (libc, -lc)


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.

     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 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 _setjmp()/_longjmp() function pairs save and restore only the reg-
     ister set and the stack.  (See sigmask(2).)

     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 porta-
     bility.


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 ALSO

     sigaction(2), sigaltstack(2), signal(3)


STANDARDS

     The setjmp() and longjmp() functions conform to ANSI X3.159-1989
     (``ANSI C89'').  The sigsetjmp() and siglongjmp() functions conform to
     ISO/IEC 9945-1:1990 (``POSIX.1'').


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.  Further-
     more, 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 previ-
     ously thought.

NetBSD 3.1.1                    August 10, 2002                   NetBSD 3.1.1