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In the same vein as `Cell::take` and `Option::take`.
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Bump the bootstrap compiler
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Add undo_leak to reset RefCell borrow state
This method is complementary for the feature cell_leak added in an
earlier PR. It allows *safely* reverting the effects of leaking a borrow guard by
statically proving that such a guard could not longer exist. This was
not added to the existing `get_mut` out of concern of impacting the
complexity of the otherwise pure pointer cast and because the name
`get_mut` poorly communicates the intent of resetting remaining borrows.
This is a follow-up to #68712 and uses the same tracking issue, #69099,
as these methods deal with the same mechanism and the idea came up
[in a review comment](https://github.com/rust-lang/rust/pull/68712#discussion_r384670041).
@dtolnay who reviewed the prior PR.
cc @RalfJung
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This method is complementary for the feature refcell_leak added in an
earlier PR. It allows reverting the effects of leaking a borrow guard by
statically proving that such a guard could not longer exist. This was
not added to the existing `get_mut` out of concern of impacting the
complexity of the otherwise pure pointer cast and because the name
`get_mut` poorly communicates the intent of resetting remaining borrows.
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Add methods to 'leak' RefCell borrows as references with the lifetime of the original reference
Usually, references to the interior are only created by the `Deref` and
`DerefMut` impl of the guards `Ref` and `RefMut`. Note that `RefCell`
already has to cope with leaks of such guards which, when it occurs,
effectively makes it impossible to ever acquire a mutable guard or any
guard for `Ref` and `RefMut` respectively. It is already safe to use
this to create a reference to the inner of the ref cell that lives as
long as the reference to the `RefCell` itself, e.g.
```rust
fn leak(r: &RefCell<usize>) -> Option<&usize> {
let guard = r.try_borrow().ok()?;
let leaked = Box::leak(Box::new(guard));
Some(&*leaked)
}
```
The newly added methods allow the same reference conversion without an
indirection over a leaked allocation. It's placed on the `Ref`/`RefMut` to
compose with both borrow and try_borrow directly.
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Usually, references to the interior are only created by the `Deref` and
`DerefMut` impl of the guards `Ref` and `RefMut`. Note that `RefCell`
already has to cope with leaks of such guards which, when it occurs,
effectively makes it impossible to ever acquire a mutable guard or any
guard for `Ref` and `RefMut` respectively. It is already safe to use
this to create a reference to the inner of the ref cell that lives as
long as the reference to the `RefCell` itself, e.g.
```rust
fn leak(r: &RefCell<usize>) -> Option<&usize> {
let guard = r.try_borrow().ok()?;
let leaked = Box::leak(Box::new(guard));
Some(&*leaked)
}
```
The newly added methods allow the same reference conversion without an
indirection over a leaked allocation and composing with both borrow and
try_borrow without additional method combinations.
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functions with a `const` modifier
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Co-Authored-By: Mazdak Farrokhzad <twingoow@gmail.com>
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Have tidy ensure that we document all `unsafe` blocks in libcore
cc @rust-lang/libs
I documented a few and added ignore flags on the other files. We can incrementally document the files, but won't regress any files this way.
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To make `new` method appear first in documentation.
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Optimize RefCell read borrowing
Instead of doing two comparisons we can do only one with a bit of cleverness.
LLVM currently can't do this optimization itself on x86-64.
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Instead of doing two comparisons we can do only one with a bit of
cleverness.
LLVM currently can't do this optimization itself on x86-64.
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FCP: https://github.com/rust-lang/rust/issues/43038#issuecomment-499900463
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Stabilize RefCell::try_borrow_unguarded
Servo has been using this since https://github.com/servo/servo/pull/23196 to add a runtime check to some unsafe code, as discussed in PR https://github.com/rust-lang/rust/pull/59211. Stabilizing would help do more of the same in libraries that also have users on Stable.
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Servo has been using this since https://github.com/servo/servo/pull/23196 to add a runtime check to some unsafe code, as discussed in PR https://github.com/rust-lang/rust/pull/59211. Stabilizing would help do more of the same in libraries that also have users on Stable.
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Introduce RefCell::try_borrow_unguarded
*Come sit next to the fireplace with me, this is going to be a long story.*
So, you may already be aware that Servo has weird design constraints that forces us developers working on it to do weird things. The thing that interests us today is that we do layout on a separate thread with its own thread pool to do some things in parallel, whereas the data it uses comes from the script thread, which implements the entire DOM and related pieces, with `!Sync` data types such as `RefCell<T>`.
The invariant we maintain is that script does not do anything ever with the DOM data as long as layout is doing its job. That's all nice and all, but one thing we don't ensure is that we don't actually know if script was currently mutably borrowing some `RefCell<T>` prior to starting layout, which may lead to aliasing mutable memory and obviously undefined behaviour.
This PR reinstates `RefCell::borrow_state` so that [this method](https://github.com/servo/servo/blob/master/components/script/dom/bindings/cell.rs#L23-L30) can make use of it and return `None` if the cell was mutably borrowed.
Cc @SimonSapin
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Stabilize refcell_replace_swap feature
Please be kind, this is my first time contributing. :smile:
I noticed #43570 only needs stabilizing (and I need it for a side project I'm working on), so I followed the [guide](https://rust-lang.github.io/rustc-guide/stabilization_guide.html#stabilization-pr) to move things forward.
I'm happy to amend things if needed, let me know!
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This replaces RefCell::borrow_state to something that encodes the use
case of Servo better.
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- Closes #51476
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This reverts commit dc2d5058e999abb18ab2686b4e3e385ec6e36666.
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