makecontext(3C)                                             makecontext(3C)

NAME
     makecontext, swapcontext - amend user contexts

SYNOPSIS
     #include <ucontext.h>

     void makecontext(ucontextt *ucp, (void(*)())func, int argc,...);

     int swapcontext(ucontextt *oucp, ucontextt *ucp);

DESCRIPTION
     These functions are useful for implementing user-level context switch-
     ing 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.

     The makecontext() will fail if:

     EFAULT    ucp or oucp points to an invalid address.

     The swapcontext() will fail if:

     ENOMEM    ucp does not have enough stack left to complete the opera-
               tion.

RESULT
     On successful completion, swapcontext() returns a value of zero. Oth-
     erwise, a value of -1 is returned and errno is set to indicate the
     error.

NOTES
     The size of the ucontextt 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.

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








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