Wrap R_MAIN in an UnsafeCell
#664
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DavisVaughan
approved these changes
Jan 10, 2025
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| /// We use the `once_cell` crate for init synchronisation because the stdlib | ||
| /// equivalent `std::sync::Once` does not have a `wait()` method. | ||
| static R_INIT: once_cell::sync::OnceCell<()> = once_cell::sync::OnceCell::new(); |
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Looks like wait() is a nightly method that may get stabilized soon ish https://doc.rust-lang.org/std/sync/struct.OnceLock.html#method.wait
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| // We extend the lifetime to `'static` as `R_MAIN` is effectively static once initialized. | ||
| // This allows us to return a `&mut` from the unsafe cell to the caller. | ||
| unsafe { std::mem::transmute::<&mut RMain, &'static mut RMain>(main_ref) } |
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The alternative is to remove get_mut() in favor of the with_mut() everywhere right?
Since effectively what we are bypassing here is "the reference may outlive the object" kind of compiler errors?
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Correct. I went for minimal changes here.
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Also I don't think this transmute is problematic since R_MAIN is effectively 'static after init.
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Progress towards #661.
Workaround for #663 (see this issue for context).
Supersedes and closes #662.
Make
R_MAINa thread-local variable as this is a nicer way of controlling accesses from other threads.Wrap it in an
UnsafeCellso we're able to create multiple&mutto it without compilation warning. This bypasses the borrow checker and causes undefined behaviour. No changes from the status quo in this regard. Alternatively we could pass raw pointers around but that would require lots ofunsafemarkers everywhere to call methods or set state. So accepting the UB is the easiest way to fix the warning until we can do better.