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.\" $FreeBSD$
.\"
.Dd Sep 10, 2002
.Dt MAKECONTEXT 3
.Os
.Sh NAME
.Nm makecontext
.Nm swapcontext
.Nd modify and exchange user thread contexts
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In ucontext.h
.Ft void
.Fn makecontext "ucontext_t *ucp" "void (*func)()" "int argc" "..."
.Ft int
.Fn swapcontext "ucontext_t *oucp" "const ucontext_t *ucp"
.Sh DESCRIPTION
.Fn makecontext
modifies the user thread context pointed to by
.Fa ucp ,
which must have previously been initialized by a call to
.Fn getcontext
and had a stack allocated for it.
The context is modified so that it will continue execution by invoking
.Fn func
with the arguments provided.
.Fa argc
must be equal to the number of additional arguments provided to
.Fn makecontext
and also equal to the number of parameters to
.Fn func ,
or else the behavior is undefined.
.Pp
.Fa "ucp->uc_link"
must be initialized before calling
.Fn makecontext
and determines the action to take when
.Fn func
returns:
if equal to
.Dv NULL ,
the process exits;
otherwise,
.Fn setcontext "ucp->uc_link"
is implicitly invoked.
.Pp
.Fn swapcontext
saves the current thread context in
.Fa "*oucp"
and makes
.Fa "*ucp"
the currently active context.
.Sh RETURN VALUES
If successful,
.Fn swapcontext
returns zero;
otherwise -1 is returned and
.Va errno
is set appropriately.
.Sh ERRORS
.Fn swapcontext
will fail if:
.Bl -tag -width Er
.It Bq Er ENOMEM
There is not enough stack space in
.Fa ucp
to complete the operation.
.El
.Sh SEE ALSO
.Xr setcontext 3 ,
.Xr ucontext 3