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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 modi-
       fied so that it will continue execution by invoking func() with the ar-
       guments provided.  The argc argument must be equal to the number	of ad-
       ditional	arguments of type int provided to makecontext()	and also equal
       to the number of	arguments of type int to func(); otherwise ,  the  be-
       havior 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	speci-
       fication.

       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	13.2			March 23, 2020			MAKECONTEXT(3)
NAME | LIBRARY | SYNOPSIS | DESCRIPTION | RETURN VALUES | ERRORS | SEE ALSO | STANDARDS | HISTORY

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