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MAKECONTEXT(3)		     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  in-
     voked.

     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 In-
     terfaces 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 makecon-
     text() and swapcontext() as obsolete, citing portability issues and  recom-
     mending  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 im-
     plementation  detail  that  it may be possible to pass pointer arguments to
     functions.

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

FreeBSD ports 15.quarterly	 March 23, 2020 		  MAKECONTEXT(3)

Want to link to this manual page? Use this URL:
<https://man.freebsd.org/cgi/man.cgi?query=swapcontext&sektion=3&manpath=FreeBSD+15.1-RELEASE+and+Ports.quarterly>

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