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GETCONTEXT(3P)             POSIX Programmer's Manual            GETCONTEXT(3P)



PROLOG
       This manual page is part of the POSIX Programmer's Manual.  The Linux implementation of this interface may dif-
       fer (consult the corresponding Linux manual page for details of Linux behavior), or the interface  may  not  be
       implemented on Linux.

NAME
       getcontext, setcontext - get and set current user context

SYNOPSIS
       #include <ucontext.h>

       int getcontext(ucontext_t *ucp);
       int setcontext(const ucontext_t *ucp);


DESCRIPTION
       The  getcontext()  function shall initialize the structure pointed to by ucp to the current user context of the
       calling thread. The ucontext_t type that ucp points to defines the user context and includes  the  contents  of
       the calling thread's machine registers, the signal mask, and the current execution stack.

       The  setcontext()  function shall restore the user context pointed to by ucp. A successful call to setcontext()
       shall 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 makecontext(), 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(), program execution continues with the function  passed  to  makecontext().   When  that  function
       returns,  the  thread shall continue as if after a call to setcontext() with the ucp argument that was input to
       makecontext(). 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 thread shall exit when this context returns. The effects of
       passing a ucp argument obtained from any other source are unspecified.

RETURN VALUE
       Upon successful completion, setcontext() shall not return and getcontext() shall return 0; otherwise,  a  value
       of -1 shall be returned.

ERRORS
       No errors are defined.

       The following sections are informative.

EXAMPLES
       Refer to makecontext().

APPLICATION USAGE
       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(), then it is unspecified whether the context at the time  of  the
       corresponding  setjmp() call is restored and thus whether future calls to getcontext() provide an accurate rep-
       resentation of the current context, since the context restored by longjmp() does not  necessarily  contain  all
       the information that setcontext() requires. Signal handlers should use siglongjmp() or setcontext() instead.

       Conforming applications should not modify or access the uc_mcontext member of ucontext_t. A conforming applica-
       tion cannot assume that context includes any process-wide static data, possibly including errno. Users  manipu-
       lating contexts should take care to handle these explicitly when required.

       Use of contexts to create alternate stacks is not defined by this volume of IEEE Std 1003.1-2001.

RATIONALE
       None.

FUTURE DIRECTIONS
       None.

SEE ALSO
       bsd_signal(),  makecontext(),  setcontext(), setjmp(), sigaction(), sigaltstack(), siglongjmp(), sigprocmask(),
       sigsetjmp(), the Base Definitions volume of IEEE Std 1003.1-2001, <ucontext.h>

COPYRIGHT
       Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003 Edition, Stan-
       dard  for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifica-
       tions Issue 6, Copyright (C) 2001-2003 by the Institute of Electrical and Electronics Engineers,  Inc  and  The
       Open Group. In the event of any discrepancy between this version and the original IEEE and The Open Group Stan-
       dard, the original IEEE and The Open Group Standard is the referee  document.  The  original  Standard  can  be
       obtained online at http://www.opengroup.org/unix/online.html .



IEEE/The Open Group                  2003                       GETCONTEXT(3P)