⚡ zvariant, zbus: use borrowed clone if possible #407
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This change implements `Signature::as_ref()` to get a borrowed clone of a `Signature`. The code is a copy of `Str::as_ref()`.
The variants `MessageField::Path` and `MessageField::Signature` might own their data. Both variants wrap `Str` and `Bytes`, resp., which use `Arc<[_]>` for their owned data. Even though cloning an `Arc` is cheap, it's not exactly for free. An atomic increment has some inherent overhead, and `Arc::clone()` also `panic!()`s if there are excessively many strong references to an `Arc`. For every `panic!()` some code to unwind the stack has to be generated, which hurts cache locality, and bloats the generated code.
This change replaces `Signature::clone()` with `Signature::as_ref()` where possible. This makes the generated code slightly more dense, because there can be no `panic!()`s, and slightly faster, because no exclusive access to the strong reference counter has the be acquired, e.g. through a `lock` prefix on amd64. No function signatures were changed.
zeenix
approved these changes
Jul 16, 2023
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This PR implements
Signature::as_ref()to get a borrowed clone of aSignature. The code is a copy ofStr::as_ref().Even though cloning an
Arcis cheap, it's not exactly for free. An atomic increment has some inherent overhead, andArc::clone()alsopanic!()s if there are excessively many strong references to anArc. For everypanic!()some code to unwind the stack has to be generated, which hurts cache locality, and bloats the generated code.