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FreeBSD 11.0 - man page for makecontext (freebsd section 3)

MAKECONTEXT(3)						   BSD Library Functions Manual 					    MAKECONTEXT(3)

NAME
makecontext, swapcontext -- modify and exchange user thread contexts
LIBRARY
Standard C Library (libc, -lc)
SYNOPSIS
#include <ucontext.h> void makecontext(ucontext_t *ucp, void (*func)(void), int argc, ...); int swapcontext(ucontext_t *oucp, const ucontext_t *ucp);
DESCRIPTION
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 argu- ments 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 implicitly invoked. The swapcontext() function saves the current thread context in *oucp and makes *ucp the currently active context.
RETURN VALUES
If successful, swapcontext() returns zero; otherwise -1 is returned and the global variable errno is set appropriately.
ERRORS
The swapcontext() function will fail if: [ENOMEM] There is not enough stack space in ucp to complete the operation.
SEE ALSO
setcontext(3), ucontext(3)
BSD
September 10, 2002 BSD