MAKECONTEXT(P) POSIX Programmer's Manual MAKECONTEXT(P)
makecontext, swapcontext - manipulate user contexts
void makecontext(ucontext_t *ucp, void (*func)(void),
int argc, ...);
int swapcontext(ucontext_t *restrict oucp,
const ucontext_t *restrict ucp);
The makecontext() function shall modify the context specified by ucp, which has been ini-
tialized using getcontext(). When this context is resumed using swapcontext() or setcon-
text(), program execution shall continue by calling func, passing it the arguments that
follow argc in the makecontext() call.
Before a call is made to makecontext(), the application shall ensure that the context
being modified has a stack allocated for it. The application shall ensure that the value
of argc matches the number of arguments of type int passed to func; otherwise, the behav-
ior is undefined.
The uc_link member is used to determine the context that shall be resumed when the context
being modified by makecontext() returns. The application shall ensure that the uc_link
member is initialized prior to the call to makecontext().
The swapcontext() function shall save the current context in the context structure pointed
to by oucp and shall set the context to the context structure pointed to by ucp.
Upon successful completion, swapcontext() shall return 0. Otherwise, -1 shall be returned
and errno set to indicate the error.
The swapcontext() function shall fail if:
ENOMEM The ucp argument does not have enough stack left to complete the operation.
The following sections are informative.
The following example illustrates the use of makecontext():
static ucontext_t ctx;
ctx.uc_stack.ss_sp = st1;
ctx.uc_stack.ss_size = sizeof st1;
ctx.uc_link = &ctx;
makecontext(&ctx, f1, 0);
ctx.uc_stack.ss_sp = st2;
ctx.uc_stack.ss_size = sizeof st2;
ctx.uc_link = &ctx;
makecontext(&ctx, f2, 0);
exit() , getcontext() , sigaction() , sigprocmask() , the Base Definitions volume of
IEEE Std 1003.1-2001, <ucontext.h>
Portions of this text are reprinted and reproduced in electronic form from IEEE Std
1003.1, 2003 Edition, Standard for Information Technology -- Portable Operating System
Interface (POSIX), The Open Group Base Specifications Issue 6, Copyright (C) 2001-2003 by
the Institute of Electrical and Electronics Engineers, Inc and The Open Group. In the
event of any discrepancy between this version and the original IEEE and The Open Group
Standard, the original IEEE and The Open Group Standard is the referee document. The orig-
inal Standard can be obtained online at http://www.opengroup.org/unix/online.html .
IEEE/The Open Group 2003 MAKECONTEXT(P)