makecontext(3) [netbsd man page]

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 num-
     ber 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 (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 specifica-
     tion.

     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

Check Out this Related Man Page

MAKECONTEXT(3)						     Linux Programmer's Manual						    MAKECONTEXT(3)

NAME

       makecontext, swapcontext - manipulate user context

SYNOPSIS

       #include <ucontext.h>

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

DESCRIPTION

       In a SysV-like environment, one has the type ucontext_t defined in <ucontext.h> and the four functions getcontext(), setcontext(), makecon-
       text() and swapcontext() that allow user-level context switching between multiple threads of control within a process.

       For the type and the first two functions, see getcontext(2).

       The makecontext() function modifies the context pointed to by ucp (which was obtained from a call to getcontext()).  Before  calling  make-
       context(),  one	should	allocate  a  new  stack for this context, assigning to ucp->uc_stack, and define a successor context, assigning to
       ucp->uc_link.  When this context is later activated (using setcontext() or swapcontext()) then first the function func is called, with  the
       arguments  specified  following argc (where argc must contain the number of these arguments), and when this function returns, the successor
       context is activated. When the successor context pointer is NULL, the thread exits.

       The swapcontext() function saves the current context in the structure pointed to by oucp, and then activates the context pointed to by ucp.

RETURN VALUE

       When successful, makecontext() returns 0 and swapcontext() does not return. (But we may return later, in case oucp is activated,  in  which
       case it looks like swapcontext() returns 0.)  On error, both return -1 and set errno appropriately.

ERRORS

       ENOMEM Insufficient stack space left.

NOTES

       The interpretation of ucp->uc_stack is just as in sigaltstack(2), namely, this struct contains start and length of a memory area to be used
       as stack, regardless of the direction of growth of the stack. So, it is not necessary for the user program to worry about this direction.

CONFORMING TO

       SUSv2, POSIX 1003.1-2001.

SEE ALSO

       getcontext(2), sigaction(2), sigaltstack(2), sigprocmask(2), sigsetjmp(3)

Linux 2.4							    2001-11-15							    MAKECONTEXT(3)

Linux and UNIX Man Pages

makecontext(3) [netbsd man page]

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