refactor: use ArcSwap and remove Mutex

[timtorChen]

Related issue: #44

[gemini-code-assist]

Summary of Changes

Hello @timtorChen, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request refactors the RusticCollector to enhance its concurrency model by replacing the std::sync::Mutex with the arc-swap crate. This change aims to provide more efficient and lock-free access to the repository and snapshot data, improving performance and reducing the complexity associated with mutex-based synchronization in an asynchronous context.

Highlights

• Concurrency Refactoring: Replaced std::sync::Mutex with arc-swap for managing shared state within the RusticCollector, improving concurrency and reducing potential deadlocks.
• Dependency Update: Updated the arc-swap crate to version 1.8.2 and added it as a direct dependency to Cargo.toml.
• State Management Simplification: Removed the internal State struct, directly managing the repository and snapshots using ArcSwap within the RusticCollector.
• Asynchronous Data Handling: Adapted data update and repository initialization logic to leverage ArcSwap's atomic reference counting for efficient, lock-free access.

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Changelog

• Cargo.lock
  • Updated arc-swap dependency from 1.7.1 to 1.8.2.
  • Added rustversion as a dependency for arc-swap.
  • Added arc-swap as a direct dependency for rustic-exporter.
• Cargo.toml
  • Added arc-swap = "1.8.2" as a new dependency.
• src/collector.rs
  • Imported arc_swap::ArcSwap.
  • Removed the State struct definition.
  • Modified RusticCollector to use ArcSwap<Option<Repository>> for repository and ArcSwap<Vec<SnapshotFile>> for snapshots, replacing the Arc<Mutex<State>>.
  • Updated the new function to return Arc<Self> and initialize ArcSwap instances.
  • Refactored set_repository to store the Repository in ArcSwap.
  • Renamed update_data to update_snpashot and updated its implementation to use ArcSwap for snapshot updates.
  • Adjusted the Collector::encode method to retrieve repository and snapshot data directly from ArcSwap instances.

Activity

• No specific activity (comments, reviews, progress updates) has been recorded for this pull request yet.

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[codecov]

Codecov Report

❌ Patch coverage is 0% with 35 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
src/collector.rs	0.00%	35 Missing ⚠️

Files with missing lines	Coverage Δ
src/collector.rs	0.00% <0.00%> (ø)

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[gemini-code-assist]

Code Review

This pull request refactors the collector to use ArcSwap instead of a Mutex for managing shared state, which is a great improvement for concurrent access. The implementation is mostly correct, but I've found a critical performance regression in the encode method that should be addressed. I've also pointed out a minor typo. Please see my detailed comments.

[timtorChen]

/gemini review

[gemini-code-assist]

Code Review

This pull request refactors the RusticCollector to use arc-swap instead of a Mutex for managing the shared state of repository and snapshots. This is a great improvement as it allows for lock-free reads, which should improve performance, especially under contention. The implementation is well-done. I've identified a critical issue that will prevent compilation, and a minor typo.

[gemini-code-assist]

Changing the return type of new to Arc<Self> is a good move for sharing the collector. However, this breaks its usage in main.rs where it's registered with prometheus-client. Registry::register_collector expects a Box<dyn Collector>, but Box<Arc<RusticCollector>> cannot be used as such because Arc<RusticCollector> doesn't implement Collector.

To fix this, you can implement Collector for Arc<RusticCollector>. Please add the following to this file:

impl Collector for Arc<RusticCollector> {
    fn encode(&self, encoder: DescriptorEncoder) -> Result<(), std::fmt::Error> {
        self.as_ref().encode(encoder)
    }
}

This will allow Box::new(arc_collector) to be treated as a Box<dyn Collector>.

[timtorChen]

The type looks wrong, but it's common, and works due to Rust’s deref coercion.
Arc<RusticCollector> derefs to &RusticCollector, so prometheus-client can call encode on it.

doc: https://doc.rust-lang.org/book/ch15-02-deref.html