Function guard

user/src/bin/stackful_coroutine.rs:210–215

This is our guard function that we place on top of the stack. All this function does is set the state of our current task and then `yield` which will then schedule a new task to be run.

()

/// This is our guard function that we place on top of the stack. All this function does is set the
/// state of our current task and then `yield` which will then schedule a new task to be run.
fn guard() {
    unsafe {
        let rt_ptr = RUNTIME as *mut Runtime;
        (*rt_ptr).t_return();
    };
}

/// We know that Runtime is alive the length of the program and that we only access from one core
/// (so no datarace). We yield execution of the current task  by dereferencing a pointer to our