MAKECONTEXT(3)						     Linux Programmer's Manual						    MAKECONTEXT(3)

NAME

       makecontext, swapcontext - manipulate user context

SYNOPSIS

       #include <ucontext.h>

       void makecontext(ucontext_t *ucp, void *func(), int argc, ...);
       int swapcontext (ucontext_t *oucp, ucontext_t *ucp);

DESCRIPTION

       In a SysV-like environment, one has the type ucontext_t defined in <ucontext.h> and the four functions getcontext(), setcontext(), makecon-
       text() and swapcontext() that allow user-level context switching between multiple threads of control within a process.

       For the type and the first two functions, see getcontext(2).

       The makecontext() function modifies the context pointed to by ucp (which was obtained from a call to getcontext()).  Before  calling  make-
       context(),  one	should	allocate  a  new  stack for this context, assigning to ucp->uc_stack, and define a successor context, assigning to
       ucp->uc_link.  When this context is later activated (using setcontext() or swapcontext()) then first the function func is called, with  the
       arguments  specified  following argc (where argc must contain the number of these arguments), and when this function returns, the successor
       context is activated. When the successor context pointer is NULL, the thread exits.

       The swapcontext() function saves the current context in the structure pointed to by oucp, and then activates the context pointed to by ucp.

RETURN VALUE

       When successful, makecontext() returns 0 and swapcontext() does not return. (But we may return later, in case oucp is activated,  in  which
       case it looks like swapcontext() returns 0.)  On error, both return -1 and set errno appropriately.

ERRORS

       ENOMEM Insufficient stack space left.

NOTES

       The interpretation of ucp->uc_stack is just as in sigaltstack(2), namely, this struct contains start and length of a memory area to be used
       as stack, regardless of the direction of growth of the stack. So, it is not necessary for the user program to worry about this direction.

CONFORMING TO

       SUSv2, POSIX 1003.1-2001.

SEE ALSO

       getcontext(2), sigaction(2), sigaltstack(2), sigprocmask(2), sigsetjmp(3)

Linux 2.4							    2001-11-15							    MAKECONTEXT(3)