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MAKECONTEXT(3) FreeBSD Library Functions Manual MAKECONTEXT(3)
NAME
makecontext, swapcontext - modify and exchange user thread contexts
LIBRARY
Standard C Library (libc, -lc)
SYNOPSIS
#include <ucontext.h>
void
makecontext(ucontext_t *ucp, void (*func)(void), int argc, ...);
int
swapcontext(ucontext_t *oucp, const ucontext_t *ucp);
DESCRIPTION
The makecontext() 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
setcontext(3), ucontext(3)
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.
System V Release 4 UNIX.
FreeBSD 14.0-RELEASE-p11 March 23, 2020 FreeBSD 14.0-RELEASE-p11