NAME
getcontext, setcontext - get and set current user context
SYNOPSIS
#include <ucontext.h>
int getcontext(ucontext_t *ucp);
int setcontext(const ucontext_t *ucp);
DESCRIPTION
The getcontext() function shall initialize the structure pointed to by
ucp to the current user context of the calling thread. The ucontext_t
type that ucp points to defines the user context and includes the
contents of the calling thread’s machine registers, the signal mask,
and the current execution stack.
The setcontext() function shall restore the user context pointed to by
ucp. A successful call to setcontext() shall not return; program
execution resumes at the point specified by the ucp argument passed to
setcontext(). The ucp argument should be created either by a prior call
to getcontext() or makecontext(), or by being passed as an argument to
a signal handler. If the ucp argument was created with getcontext(),
program execution continues as if the corresponding call of
getcontext() had just returned. If the ucp argument was created with
makecontext(), program execution continues with the function passed to
makecontext(). When that function returns, the thread shall continue
as if after a call to setcontext() with the ucp argument that was input
to makecontext(). If the uc_link member of the ucontext_t structure
pointed to by the ucp argument is equal to 0, then this context is the
main context, and the thread shall exit when this context returns. The
effects of passing a ucp argument obtained from any other source are
unspecified.
RETURN VALUE
Upon successful completion, setcontext() shall not return and
getcontext() shall return 0; otherwise, a value of -1 shall be
returned.
ERRORS
No errors are defined.
The following sections are informative.
EXAMPLES
Refer to makecontext() .
APPLICATION USAGE
When a signal handler is executed, the current user context is saved
and a new context is created. If the thread leaves the signal handler
via longjmp(), then it is unspecified whether the context at the time
of the corresponding setjmp() call is restored and thus whether future
calls to getcontext() provide an accurate representation of the current
context, since the context restored by longjmp() does not necessarily
contain all the information that setcontext() requires. Signal handlers
should use siglongjmp() or setcontext() instead.
Conforming applications should not modify or access the uc_mcontext
member of ucontext_t. A conforming application cannot assume that
context includes any process-wide static data, possibly including
errno. Users manipulating contexts should take care to handle these
explicitly when required.
Use of contexts to create alternate stacks is not defined by this
volume of IEEE Std 1003.1-2001.
RATIONALE
None.
FUTURE DIRECTIONS
None.
SEE ALSO
bsd_signal() , makecontext() , setcontext() , setjmp() , sigaction() ,
sigaltstack() , siglongjmp() , sigprocmask() , sigsetjmp() , the Base
Definitions volume of IEEE Std 1003.1-2001, <ucontext.h>
COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
Electrical and Electronics Engineers, Inc and The Open Group. In the
event of any discrepancy between this version and the original IEEE and
The Open Group Standard, the original IEEE and The Open Group Standard
is the referee document. The original Standard can be obtained online
at http://www.opengroup.org/unix/online.html .