29 lines
994 B
Rust
29 lines
994 B
Rust
use std::cell::UnsafeCell;
|
|
use std::mem;
|
|
|
|
// Like `&mut *x.get()`, but without intermediate raw pointers.
|
|
#[allow(mutable_transmutes)]
|
|
unsafe fn unsafe_cell_get<T>(x: &UnsafeCell<T>) -> &'static mut T {
|
|
mem::transmute(x)
|
|
}
|
|
|
|
fn main() { unsafe {
|
|
let c = &UnsafeCell::new(UnsafeCell::new(0));
|
|
let inner_uniq = &mut *c.get();
|
|
let inner_shr = &*inner_uniq;
|
|
// stack: [c: SharedReadWrite, inner_uniq: Unique, inner_shr: SharedReadWrite]
|
|
|
|
let _val = c.get().read(); // invalidates inner_uniq
|
|
// stack: [c: SharedReadWrite, inner_uniq: Disabled, inner_shr: SharedReadWrite]
|
|
|
|
// We have to be careful not to add any raw pointers above inner_uniq in
|
|
// the stack, hence the use of unsafe_cell_get.
|
|
let _val = *unsafe_cell_get(inner_shr); // this still works
|
|
|
|
*c.get() = UnsafeCell::new(0); // now inner_shr gets invalidated
|
|
// stack: [c: SharedReadWrite]
|
|
|
|
// now this does not work any more
|
|
let _val = *inner_shr.get(); //~ ERROR borrow stack
|
|
} }
|