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 integer value of argc must match the number of arguments that
     follow argc.  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.

     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.

BUGS
     Due to the procedure calling conventions on the MIPS processor and
     restrictions of stdarg(5), the arguments that follow the argc parameter
     for makecontext are restricted to longs and pointers only.


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.


                                                                        Page 2