getcontext(2)                                                 getcontext(2)




 NAME    [Toc]    [Back]
      getcontext, setcontext - get and  set  current  user context

 SYNOPSIS    [Toc]    [Back]
      #include <ucontext.h>

      int getcontext(ucontext_t *ucp);

      int setcontext(const ucontext_t *ucp);

 DESCRIPTION    [Toc]    [Back]
      The getcontext() function initializes the structure pointed to by ucp
      to the current user context of the calling process. The ucontext_t
      type that ucp points to defines the user context and includes the
      contents of the calling process' machine registers, the signal mask,
      and the current execution stack.

      The setcontext() function restores the user context pointed to by ucp.
      A successful call to setcontext() does 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 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 created with makecontext(),
      program execution continues with the function passed to makecontext().
      When that function returns, the process continues as if after a call
      to setcontext() with the ucp argument that was input to makecontext().
      If the ucp argument was passed to a signal handler, program execution
      continues with the program instruction following the instruction
      interrupted by the signal. 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 process will exit when this
      context returns. The effects of passing a ucp argument obtained from
      any other source are unspecified.

 RETURN VALUE    [Toc]    [Back]
      On successful completion, setcontext() does not return and
      getcontext() returns 0. Otherwise, a value of -1 is returned.

 WARNINGS    [Toc]    [Back]
      Context APIs are not recommended due to possible compatibility
      problems from release to release, because context APIs are very
      architecture-specific.  The context APIs "expose" the architecture to
      the application, such that the application may not be compatible with
      all releases.

      If you must use context APIs, be aware of the following:

      +  Do not copy the context yourself.  It is not contiguous.  The
         context may have pointers that may point back to the original



 Hewlett-Packard Company            - 1 -   HP-UX 11i Version 2: August 2003






 getcontext(2)                                                 getcontext(2)




         context rather than in the copied context; hence, it will be
         broken.

      +  The size of the context will vary in length from release to
         release.

 ERRORS    [Toc]    [Back]
      No errors are defined.

 APPLICATION USAGE    [Toc]    [Back]
      When a signal handler is executed, the current user context is saved
      and a new context is created. If the process 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() will provide an accurate representation of the
      current context, since the context restored by longjmp() may not
      contain all the information that setcontext() requires. Signal
      handlers should use siglongjmp() or setcontext() instead.

      Portable applications should not modify or access the uc_mcontext
      member of ucontext_t.  A portable 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.

 SEE ALSO    [Toc]    [Back]
      bsd_signal(), makecontext(2), setjmp(3C), sigaction(2),
      sigaltstack(2), sigprocmask(2), sigsetjmp(), <ucontext.h>.

 CHANGE HISTORY    [Toc]    [Back]
      First released in Issue 4, Version 2.


 Hewlett-Packard Company            - 2 -   HP-UX 11i Version 2: August 2003