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
)
),
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.
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(
).
)
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'') .
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.