getcontext, setcontext - get and set current user context
#include <ucontext.h>
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(3C), program execution continues with
the function passed to makecontext(3C). When that function 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 unspecified.
On successful completion, setcontext() does not return and
getcontext() returns 0. Otherwise, −1 is returned.
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(3C), then it is unspecified whether the context at the time of
the corresponding setjmp(3C) 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(3C) 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 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.
See attributes(7) for descriptions of the following attributes:
| ATTRIBUTE
TYPE |
ATTRIBUTE VALUE |
| Interface Stability |
Standard |