MAKECONTEXT(P) POSIX Programmer's Manual MAKECONTEXT(P)NAME
makecontext, swapcontext - manipulate user contexts
SYNOPSIS
#include <ucontext.h>
void makecontext(ucontext_t *ucp, void (*func)(void),
int argc, ...);
int swapcontext(ucontext_t *restrict oucp,
const ucontext_t *restrict ucp);
DESCRIPTION
The makecontext() function shall modify the context specified by ucp,
which has been initialized using getcontext(). When this context is
resumed using swapcontext() or setcontext(), 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 behavior is unde‐
fined.
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 con‐
text structure pointed to by oucp and shall set the context to the con‐
text structure pointed to by ucp.
RETURN VALUE
Upon successful completion, swapcontext() shall return 0. Otherwise, -1
shall be returned and errno set to indicate the error.
ERRORS
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.
EXAMPLES
The following example illustrates the use of makecontext():
#include <stdio.h>
#include <ucontext.h>
static ucontext_t ctx[3];
static void
f1 (void)
{
puts("start f1");
swapcontext(&ctx[1], &ctx[2]);
puts("finish f1");
}
static void
f2 (void)
{
puts("start f2");
swapcontext(&ctx[2], &ctx[1]);
puts("finish f2");
}
int
main (void)
{
char st1[8192];
char st2[8192];
getcontext(&ctx[1]);
ctx[1].uc_stack.ss_sp = st1;
ctx[1].uc_stack.ss_size = sizeof st1;
ctx[1].uc_link = &ctx[0];
makecontext(&ctx[1], f1, 0);
getcontext(&ctx[2]);
ctx[2].uc_stack.ss_sp = st2;
ctx[2].uc_stack.ss_size = sizeof st2;
ctx[2].uc_link = &ctx[1];
makecontext(&ctx[2], f2, 0);
swapcontext(&ctx[0], &ctx[2]);
return 0;
}
APPLICATION USAGE
None.
RATIONALE
None.
FUTURE DIRECTIONS
None.
SEE ALSOexit() , getcontext() , sigaction() , sigprocmask() , the Base Defini‐
tions volume of IEEE Std 1003.1-2001, <ucontext.h>
COPYRIGHT
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 original Standard can be obtained online
at http://www.opengroup.org/unix/online.html .
IEEE/The Open Group 2003 MAKECONTEXT(P)
