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 con‐
tents 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 setcon‐
text(). 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 con‐
tinues as if the corresponding call of getcontext() had just returned.
If the ucp argument was created with makecontext(3C), program execution
continues with the function passed to makecontext(3C). When that func‐
tion returns, the process continues as if after a call to setcontext()
with the ucp argument that was input to makecontext(3C). 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
On successful completion, setcontext() does not return and getcontext()
returns 0. Otherwise, −1 is returned.
No errors are defined.
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(3UCB), then it is unspecified whether the context at the
time of the corresponding setjmp(3UCB) call is restored and thus
whether future calls to getcontext() will provide an accurate represen‐
tation of the current context, since the context restored by
longjmp(3UCB) may not contain all the information that setcontext()
requires. Signal handlers should use siglongjmp(3C) instead.
Portable applications should not modify or access the uc_mcontext mem‐
ber 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
See attributes(5) for descriptions of the following attributes:
│ ATTRIBUTE TYPE │ ATTRIBUTE VALUE │
│Interface Stability │ Standard │
SEE ALSOsigaction(2), sigaltstack(2), sigprocmask(2), bsd_signal(3C), makecon‐
text(3C), setjmp(3UCB), sigsetjmp(3C), ucontext.h(3HEAD),
Feb 5, 2001 GETCONTEXT(2)