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

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 sig-
       nal 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 continues as
       if  the corresponding call of getcontext() had just returned. If the ucp argument was cre-
       ated with makecontext(), program execution continues with the function passed to  makecon-
       text().	 When that function returns, the thread shall continue as if after a call to set-
       context() 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 representation 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 setcon-
       text() instead.

       Conforming applications should not modify or access the uc_mcontext member of  ucontext_t.
       A conforming 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.

       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,	Standard  for Information Technology -- Portable Operating System
       Interface (POSIX), The Open Group Base Specifications 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
       Standard, the original IEEE and The Open Group Standard is the referee document. The orig-
       inal Standard can be obtained online at http://www.opengroup.org/unix/online.html .

IEEE/The Open Group			       2003				    GETCONTEXT(P)
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