makecontext(3C)                                      makecontext(3C)


       NAME
             makecontext, swapcontext - manipulate user contexts

       SYNOPSIS
             #include <ucontext.h>
             void makecontext (ucontext_t *ucp, (void *func)(),
                   int argc, . . . );
             int swapcontext (ucontext_t *oucp, ucontext_t *ucp);

       DESCRIPTION
             These functions are useful for implementing user-level context
             switching between multiple threads of control within a
             process.

             makecontext modifies the context specified by ucp, which has
             been initialized using getcontext; when this context is
             resumed using swapcontext or setcontext [see getcontext(2)],
             program execution continues by calling the function func,
             passing it the arguments that follow argc in the makecontext
             call.  Before a call is made to makecontext, the context being
             modified should have a stack allocated for it.  The value of
             argc must match the number of integers passed to func,
             otherwise the behavior is undefined.

             The uc_link field is used to determine the context that will
             be resumed when the context being modified by makecontext
             returns. The uc_link field should be initialized prior to the
             call to makecontext.

             swapcontext saves the current context in the context structure
             pointed to by oucp and sets the context to the context
             structure pointed to by ucp.

          Return Values
             On successful completion, swapcontext return a value of zero.
             Otherwise, a value of -1 is returned and errno is set to
             indicate the error.

          Errors
             These functions will fail if either of the following is true:

             ENOMEM
                  ucp does not have enough stack left to complete the
                  operation.




                           Copyright 1994 Novell, Inc.               Page 1

      makecontext(3C)                                      makecontext(3C)


            EFAULT
                 ucp or oucp points to an invalid address.

      REFERENCES
            exit(2), getcontext(2), sigaction(2), sigprocmask(2),
            ucontext(5)

      NOTICES
            The size of the ucontext_t structure may change in future
            releases.  To remain binary compatible, users of these
            features must always use makecontext or getcontext to create
            new instances of them.




































                          Copyright 1994 Novell, Inc.               Page 2