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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 differ (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  con-
       tents  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 execu-
       tion resumes at the point specified by the ucp argument passed to  set-
       context(). 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(), pro-
       gram execution continues 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  makecon-
       text(). 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  getcon-
       text() 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 setcontext() instead.
       Conforming applications should not modify  or  access  the  uc_mcontext
       member  of ucontext_t. A conforming application cannot assume that con-
       text 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  vol-
       ume 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 Defi-
       nitions 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 original Standard can be  obtained  online
       at http://www.opengroup.org/unix/online.html .

IEEE/The Open Group                  2003                       GETCONTEXT(3P)