GETCONTEXT(3)          FreeBSD Library Functions Manual          GETCONTEXT(3)

NAME
     getcontext, getcontextx, setcontext - get and set user thread context

LIBRARY
     Standard C Library (libc, -lc)

SYNOPSIS
     #include <ucontext.h>

     int
     getcontext(ucontext_t *ucp);

     ucontext_t *
     getcontextx(void);

     int
     setcontext(const ucontext_t *ucp);

DESCRIPTION
     The getcontext() function saves the current thread's execution context in
     the structure pointed to by ucp.  This saved context may then later be
     restored by calling setcontext().

     The getcontextx() function saves the current execution context in the
     newly allocated structure ucontext_t, which is returned on success.  If
     architecture defines additional CPU states that can be stored in extended
     blocks referenced from the ucontext_t, the memory for them may be
     allocated and their context also stored.  Memory returned by
     getcontextx() function shall be freed using free(3).

     The setcontext() function makes a previously saved thread context the
     current thread context, i.e., the current context is lost and
     setcontext() does not return.  Instead, execution continues in the
     context specified by ucp, which must have been previously initialized by
     a call to getcontext(), makecontext(3), or by being passed as an argument
     to a signal handler (see sigaction(2)).

     If ucp was initialized by getcontext(), then execution continues as if
     the original getcontext() call had just returned (again).

     If ucp was initialized by makecontext(3), execution continues with the
     invocation of the function specified to makecontext(3).  When that
     function returns, ucp->uc_link determines what happens next: if
     ucp->uc_link is NULL, the process exits; otherwise,
     setcontext(ucp->uc_link) is implicitly invoked.

     If ucp was initialized by the invocation of a signal handler, execution
     continues at the point the thread was interrupted by the signal.

RETURN VALUES
     If successful, getcontext() returns zero and setcontext() does not
     return; otherwise -1 is returned.  The getcontextx() returns pointer to
     the allocated and initialized context on success, and NULL on failure.

ERRORS
     No errors are defined for getcontext() or setcontext().  The
     getcontextx() may return the following errors in errno:

     [ENOMEM]           No memory was available to allocate for the context or
                        some extended state.

SEE ALSO
     sigaction(2), sigaltstack(2), makecontext(3), ucontext(3)

STANDARDS
     The getcontext() and setcontext() functions conform to X/Open System
     Interfaces and Headers Issue 5 ("XSH5") and IEEE Std 1003.1-2001
     ("POSIX.1").  The errno indications are an extension to the standard.

     The IEEE Std 1003.1-2004 ("POSIX.1") revision marked the functions
     getcontext() and setcontext() as obsolete, citing portability issues and
     recommending the use of POSIX threads instead.  The IEEE Std 1003.1-2008
     ("POSIX.1") revision removed the functions from the specification.

HISTORY
     The getcontext() and setcontext() functions first appeared in AT&T
     System V Release 4 UNIX.

FreeBSD 13.1-RELEASE-p6         March 23, 2020         FreeBSD 13.1-RELEASE-p6