MAKECONTEXT(3) Linux Programmer's Manual MAKECONTEXT(3)
NAME
makecontext, swapcontext - manipulate user context
SYNOPSIS
#include<ucontext.h>
voidmakecontext(ucontext_t*ucp,void*func(),int argc,...);
intswapcontext(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(), make-
context() 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 con-
text 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.
RETURNVALUE
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.
CONFORMINGTO
SUSv2, POSIX 1003.1-2001.
SEEALSO
getcontext(2), sigaction(2), sigaltstack(2), sigprocmask(2),
sigsetjmp(3)
Linux 2.4 2001-11-15 MAKECONTEXT(3)
Free eBook: 
