NAME
makecontext,
swapcontext —
manipulate user contexts
LIBRARY
library “libc”
SYNOPSIS
#include
<ucontext.h>
void
makecontext(ucontext_t
*ucp, void
(*func)(), int
argc, ...);
int
swapcontext(ucontext_t
* restrict oucp,
ucontext_t * restrict
ucp);
DESCRIPTION
Themakecontext()
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
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.