Add example for LIFO assurance to AutoRealm Drop implementation#720
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Add example for LIFO assurance to AutoRealm Drop implementation#720
AutoRealm Drop implementation#720Conversation
Signed-off-by: Euclid Ye <yezhizhenjiakang@gmail.com>
sagudev
reviewed
Mar 17, 2026
mozjs/src/realm.rs
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| // If we do not implement this, Rust can end the borrow of cx early, | ||
| // while the JSAutoRealm is still active. | ||
| // That would allow a second mutable borrow of cx before the first realm is exited, | ||
| // breaking the LIFO entering/exiting realms. |
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IIRC The real problem is that JSAutoRealm internally uses cx (it's raw ptr), so if we need to make sure that &cx remains bounded until that happens.
I think breaking LIFO is then side effect of this.
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Thanks! How about this?
// If we do not implement this, Rust can end the borrow of [JSContext]
// early while [JSAutoRealm] is still active. Since [JSAutoRealm]
// internally holds a raw pointer to the context, we must ensure the
// cx borrow remains bounded until the guard is dropped to not
// use after free and ensure strict LIFO realm entry/exit.
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There is indeed LIFO problem otherwise, so we could link it: https://play.rust-lang.org/?version=stable&mode=debug&edition=2024&gist=8799c0a41b5e007ff3b352b668dbf603
but otherwise LGTM.
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I played with the example and added some more cases.
Signed-off-by: Euclid Ye <yezhizhenjiakang@gmail.com>
sagudev
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Mar 17, 2026
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Feel free to land when done. |
yezhizhen
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AutoRealm Drop implementation
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There was some typo and wrong space.
Also add more texts based on my understanding.
Added a link for example.