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MAKECONTEXT(3)             Library Functions Manual             MAKECONTEXT(3)

     makecontext, swapcontext - manipulate user contexts

     Standard C Library (libc, -lc)

     #include <ucontext.h>

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

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

     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 execution.  When a context saved by
     swapcontext() is restored using setcontext(2), execution will resume as
     if the corresponding invocation of swapcontext() had just returned

     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.

     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

     _exit(2), getcontext(2), setcontext(2), ucontext(2)

     The makecontext() and swapcontext() functions conform to X/Open System
     Interfaces and Headers Issue 5 ("XSH5") and IEEE Std 1003.1-2001

     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

     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

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

NetBSD 10.99                      May 4, 2012                     NetBSD 10.99