NAME
getcontext
setcontext — get and set
current user context
SYNOPSIS
[OB
XSI]
#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(3),
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(3), program execution continues with the
function passed to makecontext(3). When that function
returns, the thread shall continue as if after a call to
setcontext () with the ucp argument that
was input to makecontext(3). 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.
EXAMPLES
Refer to makecontext(3).
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(3), then it is unspecified whether the context
at the time of the corresponding setjmp(3) call is
restored and thus whether future calls to getcontext
() provide an accurate representation of the current context, since the
context restored by longjmp(3) does not necessarily
contain all the information that setcontext () requires.
Signal handlers should use siglongjmp(3) 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 (“POSIX.1”).
The obsolescent functions getcontext (),
makecontext(3), and swapcontext(3) can
be replaced using POSIX threads functions.
RATIONALE
None.
FUTURE DIRECTIONS
None.
SEE ALSO
bsd_signal(3), makecontext(3), setcontext(3), setjmp(3), sigaction(3), sigaltstack(3), siglongjmp(3), sigprocmask(3), sigsetjmp(3), the Base Definitions volume of IEEE Std 1003.1-2001 (“POSIX.1”), <ucontext.h>
CHANGE HISTORY
First released in Issue 4, Version 2.
Issue 5
Moved from X/OPEN UNIX extension to BASE.
The following sentence was removed from the DESCRIPTION: "If the ucp argument was passed to a signal handler, program execution continues with the program instruction following the instruction interrupted by the signal."
Issue 6
IEEE Std 1003.1-2001
(“POSIX.1”)/Cor 2-2004, item XSH/TC2/D6/45 is applied,
updating the SYNOPSIS and APPLICATION USAGE sections to note that the
getcontext () and setcontext ()
functions are obsolescent.
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