makecontext(3) -- Linux man page
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(), 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 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)
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