MAKECONTEXT(3) Linux Programmer's Manual MAKECONTEXT(3)
makecontext, swapcontext - manipulate user context
void makecontext(ucontext_t *ucp, void *func(), int argc, ...);
int swapcontext (ucontext_t *oucp, ucontext_t *ucp);
In a SysV-like environment, one has the type ucontext_t defined in <ucontext.h> and the
four functions getcontext(), setcontext(), makecontext() 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 makecontext(), 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 suc-
cessor 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.
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.
ENOMEM Insufficient stack space left.
The interpretation of ucp->uc_stack is just as in sigaltstack(2), namely, this struct con-
tains 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
SUSv2, POSIX 1003.1-2001.
getcontext(2), sigaction(2), sigaltstack(2), sigprocmask(2), sigsetjmp(3)
Linux 2.4 2001-11-15 MAKECONTEXT(3)