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getcontext, setcontext - Initiates and restores user level context
ucontext_t *ucp );
const ucontext_t *ucp );
Interfaces documented on this reference page conform to industry standards
getcontext(), setcontext(): XSH5.0
Refer to the standards(5) reference page for more information about
industry standards and associated tags.
ucp Provides a pointer to a ucontext structure, defined in the <ucontext.h>
header file. The ucontext structure contains the signal mask,
execution stack, and machine registers. (See ucontext(5) for more
information about the format of the ucontext structure.)
Using both the getcontext() and setcontext() functions enables you to
initiate user level context control, switching between multiple threads of
control within a single process.
When you call getcontext(), it initializes the ucp argument to the current
user context of the calling process.
Use the setcontext() function to restore the state of the user context
pointed to by the ucp argument. The setcontext() function, if successful,
does not return; application execution continues from the point specified
by the ucontext structure you pass to the setcontext() function.
The ucontext structure that you pass to the setcontext() function must have
been created by a call to the getcontext() function or the makecontext()
function, or have been passed as the third argument to a signal handler.
(The third argument in a call to the sigaction() function determines the
action to be performed when a signal is delivered. For more information,
When a context structure is created by the getcontext() function, execution
of the program continues as if the corresponding call of the getcontext()
function had just returned.
When a context structure is created by the makecontext() function, program
execution continues with the function passed to makecontext(). When that
function returns, the thread continues as if after a call to setcontext()
with the context structure argument that was input to makecontext().
If the uc_link member of the ucontext_t structure pointed to by the ucp
argument is 0 (zero), then this context is the main context, and the thread
will exit when this context returns. The effects of passing a ucp argument
from any other source are unspecified.
When a signal handler executes, the current user context is saved and a new
context is created by the kernel. If the process leaves the signal handler
using the longjmp() function, the original context cannot be restored, and
the result of future calls to the getcontext() function are unpredictable.
Use the siglongjmp() or setcontext() functions in signal handlers, instead
of the longjmp() function.
The setcontext() function does not return upon success. The getcontext()
function returns 0 (zero) upon success. Upon failure, both the
setcontext() and getcontext() functions return a value of -1.
Functions: bsd_signal(2), makecontext(2), sigaction(2), sigaltstack(2),
sigprocmask(2), setjmp(3), sigsetjmp(3)
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