makecontext, swapcontext -- modify and exchange user thread contexts
Standard C Library (libc, -lc)
makecontext(ucontext_t *ucp, void (*func)(void), int argc, ...);
swapcontext(ucontext_t *oucp, const ucontext_t *ucp);
The makecontext() function modifies the user thread context pointed to by
ucp, which must have previously been initialized by a call to
getcontext(3) and had a stack allocated for it. The context is modified
so that it will continue execution by invoking func() with the arguments
provided. The argc argument must be equal to the number of additional
arguments provided to makecontext() and also equal to the number of arguments
to func(), or else the behavior is undefined.
The ucp->uc_link argument must be initialized before calling
makecontext() and determines the action to take when func() returns: if
equal to NULL, the process exits; otherwise, setcontext(ucp->uc_link) is
The swapcontext() function saves the current thread context in *oucp and
makes *ucp the currently active context.
If successful, swapcontext() returns zero; otherwise -1 is returned and
the global variable errno is set appropriately.
The swapcontext() function will fail if:
[ENOMEM] There is not enough stack space in ucp to complete the
FreeBSD 5.2.1 September 10, 2002 FreeBSD 5.2.1 [ Back ]