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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 specifi-
     cation.

     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.

HISTORY
     The makecontext() and swapcontext() functions first appeared in AT&T
     System V Release 4	UNIX.

FreeBSD	13.0			March 23, 2020			  FreeBSD 13.0

NAME | LIBRARY | SYNOPSIS | DESCRIPTION | RETURN VALUES | ERRORS | SEE ALSO | STANDARDS | HISTORY

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