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.  The integer value of argc must
         match the number of arguments that follow argc.  Otherwise the
         behavior is undefined.

         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.

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

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

         EFAULT         ucp or oucp points to an invalid address.

   SEE ALSO
         exit(2), getcontext(2), sigaction(2), sigprocmask(2), ucontext(5).

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

   NOTES
         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.








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