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 register set and the stack. (See
sigprocmask(
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 portability.
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),
sigprocmask(2),
pthread_sigmask(3),
signal(3)
STANDARDS
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”).
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. 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.