NAME
makecontext,
swapcontext —
manipulate user contexts
LIBRARY
Standard C Library (libc, -lc)
SYNOPSIS
#include <ucontext.h>
void
makecontext(
ucontext_t
*ucp,
void (*func)(),
int argc,
...);
int
swapcontext(
ucontext_t
* restrict oucp,
ucontext_t
* restrict ucp);
DESCRIPTION
The
makecontext() function modifies the object pointed to by
ucp, which has been initialized using
getcontext(2). When this
context is resumed using
swapcontext() or
setcontext(2), program
execution continues as if
func had been called with the
arguments specified after
argc in the call of
makecontext(). The value of
argc must
be equal to the number of integer arguments following it, and must be equal to
the number of integer arguments expected by
func;
otherwise, the behavior is undefined.
Before being modified using
makecontext(), a stack must be
allocated for the context (in the
uc_stack member), and
a context to resume after
func has returned must be
determined (pointed to by the
uc_link member);
otherwise, the behavior is undefined. If
uc_link is a
null pointer, then the context is the main context, and the process will exit
with an exit status of 0 upon return.
The
swapcontext() function saves the current context in the
object pointed to by
oucp, sets the current context to
that specified in the object pointed to by
ucp, and
resumes execution. When a context saved by
swapcontext() is
restored using
setcontext(2), execution
will resume as if the corresponding invocation of
swapcontext() had just returned (successfully).
RETURN VALUES
The
makecontext() function returns no value.
On success,
swapcontext() returns a value of 0, Otherwise, -1
is returned and
errno is set to indicate the error.
ERRORS
The
swapcontext() function will fail if:
-
-
- [
EFAULT
]
- The oucp argument or the
ucp argument points to an invalid address.
-
-
- [
EINVAL
]
- The contents of the datum pointed to by
ucp are invalid.
SEE ALSO
_exit(2),
getcontext(2),
setcontext(2),
ucontext(2)
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.
The standard does
not clearly define the type of integer arguments passed to
func via makecontext(); portable
applications should not rely on the implementation detail that it may be
possible to pass pointer arguments to functions.
This may be clarified in a future revision of the standard.
HISTORY
The
makecontext() and
swapcontext()
functions first appeared in
AT&T System V
Release 4 UNIX.