MirOS Manual: longjmp(3), longjmperror(3), setjmp(3), siglongjmp(3), sigsetjmp(3), _longjmp(3), _setjmp(3)

SETJMP(3)                  BSD 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 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.

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
     C"). The sigsetjmp() and siglongjmp() functions conform to IEEE Std
     1003.1-1990 ("POSIX").

CAVEATS

     Historically, on AT&TNon-Null System V UNIX, the setjmp()/longjmp() func-
     tions 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.

MirOS BSD #10-current           March 31, 2012                               1

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