NAME
makecontext,
swapcontext —
modify and exchange user thread
contexts
LIBRARY
library “libc”
SYNOPSIS
#include
<ucontext.h>
void
makecontext(ucontext_t *ucp,
void (*func)(void), int argc,
...);
int
swapcontext(ucontext_t
*oucp, const ucontext_t
*ucp);
DESCRIPTION
Themakecontext()
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 of type int
provided to makecontext() and also equal to the number
of arguments of type int to
func(); otherwise , 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
STANDARDS
The makecontext() and
swapcontext() functions conform to
X/Open System Interfaces and Headers Issue 5
(“XSH5”) and IEEE Std 1003.1-2001
(“POSIX.1”).
The IEEE Std 1003.1-2004
(“POSIX.1”) revision marked the functions
makecontext() and
swapcontext() as obsolete, citing portability issues
and recommending the use of POSIX threads instead. The IEEE
Std 1003.1-2008 (“POSIX.1”) revision removed the
functions from the specification.
makecontext(); portable applications should not rely
on the implementation detail that it may be possible to pass pointer arguments
to functions.HISTORY
The makecontext() and
swapcontext() functions first appeared in
AT&T System V Release 4 UNIX.