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NetBSD 6.1.5 - man page for swapcontext (netbsd section 3)

MAKECONTEXT(3)			   BSD Library Functions Manual 		   MAKECONTEXT(3)

NAME
     makecontext, swapcontext -- manipulate user contexts

LIBRARY
     Standard C Library (libc, -lc)

SYNOPSIS
     #include <ucontext.h>

     void
     makecontext(ucontext_t *ucp, void (*func)(), int argc, ...);

     int
     swapcontext(ucontext_t * restrict oucp, ucontext_t * restrict ucp);

DESCRIPTION
     The makecontext() 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 execu-
     tion.  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
     _exit(2), getcontext(2), setcontext(2), ucontext(2)

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.

     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.  This may be clarified in a future
     revision of the standard.

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

BSD					   May 4, 2012					      BSD


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