setup_read_cleanup

A library for managing data through distinct lifecycle phases: Setup -> Read -> Cleanup.

This crate provides "phased cells", a collection of smart pointer types that enforce a specific lifecycle for the data they manage. This is useful for data that is initialized once, read by multiple threads or tasks for a period, and then explicitly destroyed.

Core Concepts

The lifecycle is divided into three phases:

Setup: The initial phase. The data can be mutably accessed for initialization.
Read: The operational phase. The data can only be accessed immutably. This phase is optimized for concurrent, lock-free reads.
Cleanup: The final phase. The data can be mutably accessed again for deconstruction or resource cleanup.

Panic Handling in Transition Closures

The transition_to_read and transition_to_cleanup methods execute user-provided closures. If a panic occurs within these closures, PhasedCell ensures the following behavior across all its variants:

transition_to_read: If the closure panics, the cell's phase is safely reverted to Setup.
transition_to_cleanup: If the closure panics, the cell's phase is safely transitioned to Cleanup.

In both cases, any acquired internal mutexes are released before the panic is resumed, preventing deadlocks. The original panic is re-propagated, maintaining Rust's panic-safety guarantees while ensuring internal consistency.

Cell Variants

This crate offers several cell variants to suit different concurrency needs:

PhasedCell: The basic cell. It is Sync, allowing it to be shared across threads for reading. However, mutable access via get_mut_unlocked is not thread-safe and requires the caller to ensure exclusive access.
PhasedCellSync: A thread-safe version that uses a std::sync::Mutex to allow for safe concurrent mutable access during the Setup and Cleanup phases.
PhasedCellAsync: (Requires the tokio feature) An async version of PhasedCellSync that uses a tokio::sync::Mutex.

Graceful Features

(Requires the graceful feature)

The graceful module provides wrappers that add graceful capabilities to phased cells:

Graceful Cleanup: It ensures that all ongoing read operations complete before allowing the cell to fully transition to the Cleanup phase.
Graceful Read: If a read operation is attempted while the cell is in the Setup phase and transitioning to Read, the read operation will wait for the transition to complete and for the cell to enter the Read phase.

It provides the following cells:

GracefulPhasedCell
GracefulPhasedCellSync
GracefulPhasedCellAsync (Requires graceful and tokio features)

Features

tokio: Enables the async cell variants (PhasedCellAsync, GracefulPhasedCellAsync) which use tokio::sync.
graceful: Enables the graceful module, which provides cells with graceful cleanup capabilities.

Examples

Using a static PhasedCellSync to initialize data, read it from multiple threads, and then clean it up.

use setup_read_cleanup::{PhasedCellSync, Phase};
use std::thread;

struct MyData {
    items: Vec<i32>,
}

// Declare a static PhasedCellSync instance
static CELL: PhasedCellSync<MyData> = PhasedCellSync::new(MyData { items: Vec::new() });

fn main() {
    // --- Setup Phase ---
    assert_eq!(CELL.phase(), Phase::Setup);
    {
        let mut data = CELL.lock().unwrap();
        data.items.push(10);
        data.items.push(20);
    } // Lock is released here

    // --- Transition to Read Phase ---
    CELL.transition_to_read(|data| {
        data.items.push(30);
        Ok::<(), std::io::Error>(())
    }).unwrap();
    assert_eq!(CELL.phase(), Phase::Read);

    // --- Read Phase ---
    // Now, multiple threads can read the data concurrently.
    let mut handles = Vec::new();
    for i in 0..3 {
        handles.push(thread::spawn(move || {
            let data = CELL.read().unwrap(); // Access the static CELL
            println!("Thread {} reads: {:?}", i, data.items);
            assert_eq!(data.items, &[10, 20, 30]);
        }));
    }

    for handle in handles {
        handle.join().unwrap();
    }

    // --- Transition to Cleanup Phase ---
    CELL.transition_to_cleanup(|data| {
        println!("Cleaning up. Final item: {:?}", data.items.pop());
        Ok::<(), std::io::Error>(())
    }).unwrap();
    assert_eq!(CELL.phase(), Phase::Cleanup);

    println!("Example finished successfully!");
}

Installation

In Cargo.toml, write this crate as a dependency:

[dependencies]
setup_read_cleanup = "0.6.0"

Supported Rust versions

This crate supports Rust 1.74.1 or later.

% ./build.sh msrv
  [Meta]   cargo-msrv 0.18.4

Compatibility Check #1: Rust 1.74.1
  [OK]     Is compatible

Compatibility Check #2: Rust 1.65.0
  [FAIL]   Is incompatible

Compatibility Check #3: Rust 1.69.0
  [FAIL]   Is incompatible

Compatibility Check #4: Rust 1.71.1
  [FAIL]   Is incompatible

Compatibility Check #5: Rust 1.72.1
  [FAIL]   Is incompatible

Compatibility Check #6: Rust 1.73.0
  [FAIL]   Is incompatible

Result:
   Considered (min … max):   Rust 1.56.1 … Rust 1.91.1
   Search method:            bisect
   MSRV:                     1.74.1
   Target:                   x86_64-apple-darwin

License

This program is free software under MIT License. See the file LICENSE in this distribution for more details.

setup_read_cleanup 0.6.0