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