getcontext, setcontext - get and set current user context
int getcontext(ucontext_t *ucp);
int setcontext(const ucontext_t *ucp);
The getcontext() function initializes the structure pointed to by ucp
to the current user context of the calling process. The ucontext_t
type that ucp points to defines the user context and includes the
contents of the calling process' machine registers, the signal mask,
and the current execution stack.
The setcontext() function restores the user context pointed to by ucp.
A successful call to setcontext() does 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 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 process continues as if after a call
to setcontext() with the ucp argument that was input to makecontext().
If the ucp argument was passed to a signal handler, program execution
continues with the program instruction following the instruction
interrupted by the signal. 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 process will exit when this
context returns. The effects of passing a ucp argument obtained from
any other source are unspecified.
On successful completion, setcontext() does not return and
getcontext() returns 0. Otherwise, a value of -1 is returned.
Context APIs are not recommended due to possible compatibility
problems from release to release, because context APIs are very
architecture-specific. The context APIs "expose" the architecture to
the application, such that the application may not be compatible with
If you must use context APIs, be aware of the following:
+ Do not copy the context yourself. It is not contiguous. The
context may have pointers that may point back to the original
Hewlett-Packard Company - 1 - HP-UX Release 11i: November 2000
context rather than in the copied context; hence, it will be
+ The size of the context will vary in length from release to
No errors are defined.
When a signal handler is executed, the current user context is saved
and a new context is created. If the process 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() will provide an accurate representation of the
current context, since the context restored by longjmp() may not
contain all the information that setcontext() requires. Signal
handlers should use siglongjmp() or setcontext() instead.
Portable applications should not modify or access the uc_mcontext
member of ucontext_t. A portable 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.
bsd_signal(), makecontext(2), setjmp(3C), sigaction(2),
sigaltstack(2), sigprocmask(2), sigsetjmp(), <ucontext.h>.
First released in Issue 4, Version 2.
Hewlett-Packard Company - 2 - HP-UX Release 11i: November 2000