rangelockrs

range-lock - Multithread range lock for Vec
===========================================

`https://bues.ch/ `_

Provides multi-threaded access to a single Vec instance. Any thread can atomically request access to a slice of the Vec. Such access is granted, if no other thread is simultaneously holding the right to access an overlapping slice.


Usage
=====

Add this to your Cargo.toml:

.. code:: toml

[dependencies]
range-lock = "0.1"


RangeLock example usage
-----------------------

General purpose RangeLock:

.. code:: rust

extern crate range_lock;
use range_lock::RangeLock;
use std::sync::{Arc, Barrier};
use std::thread;

// The data that will simultaneously be accessed from the threads.
let data = vec![10, 11, 12, 13];

// Embed the data in a RangeLock
// and clone atomic references to it for the threads.
let data_lock0 = Arc::new(RangeLock::new(data));
let data_lock1 = Arc::clone(&data_lock0);
let data_lock2 = Arc::clone(&data_lock0);

// Thread barrier, only for demonstration purposes.
let barrier0 = Arc::new(Barrier::new(2));
let barrier1 = Arc::clone(&barrier0);

// Spawn first thread.
let thread0 = thread::spawn(move || {
{
let mut guard = data_lock0.try_lock(0..2).expect("T0: Failed to lock 0..2");
guard[0] = 100; // Write to data[0]
}
barrier0.wait(); // Synchronize with second thread.
{
let guard = data_lock0.try_lock(2..4).expect("T0: Failed to lock 2..4");
assert_eq!(guard[0], 200); // Read from data[2]
}
});

// Spawn second thread.
let thread1 = thread::spawn(move || {
{
let mut guard = data_lock1.try_lock(2..4).expect("T1: Failed to lock 2..4");
guard[0] = 200; // Write to data[2]
}
barrier1.wait(); // Synchronize with first thread.
{
let guard = data_lock1.try_lock(0..2).expect("T1: Failed to lock 0..2");
assert_eq!(guard[0], 100); // Read from data[0]
}
});

// Wait for both threads to finish and check result.
thread0.join().expect("Thread 0 failed");
thread1.join().expect("Thread 1 failed");

// Unwrap the data from the lock.
let data = Arc::try_unwrap(data_lock2).expect("Arc unwrap failed").into_inner();

// Check the data that has been modified by the threads.
assert_eq!(data, vec![100, 11, 200, 13]);


RepRangeLock example usage
--------------------------

The RepRangeLock is a restricted range lock, that provides interleaved patterns of slices to the threads.

Locking a RepRangeLock is more lightweight than locking a RangeLock.

Please see the example below.

.. code:: rust

use range_lock::RepRangeLock;
use std::sync::Arc;
use std::thread;

let data = vec![1, 2, 3, 4, 5, 6, // <- cycle 0
7, 8, 9, 10, 11, 12]; // <- cycle 1
// ^--^ ^---^ ^----^
// | | |
// offset-0 offset-1 offset-2

let lock = Arc::new(RepRangeLock::new(data,
2, // slice_len: Each slice has 2 elements.
3)); // cycle_len: Each cycle has 3 slices (offsets).
let lock0 = Arc::clone(&lock);
let lock1 = Arc::clone(&lock);
let lock2 = Arc::clone(&lock);

let thread0 = thread::spawn(move || {
// Lock slice offset 0:
let mut guard = lock0.try_lock(0).expect("Failed to lock offset.");

// Read:
assert_eq!(guard[0][0], 1); // Cycle 0, Slice element 0
assert_eq!(guard[0][1], 2); // Cycle 0, Slice element 1
// let _ = guard[0][2]; // Would panic. Slice len is only 2.
assert_eq!(guard[1][0], 7); // Cycle 1, Slice element 0
assert_eq!(guard[1][1], 8); // Cycle 1, Slice element 1
// let _ = guard[2][0]; // Would panic: The data vec is only 2 repeat cycles long.

// Write:
guard[0][0] = 10; // Cycle 0, Slice element 0
guard[0][1] = 20; // Cycle 0, Slice element 1
// guard[0][2] = 42; // Would panic: Slice len is only 2.
guard[1][0] = 30; // Cycle 1, Slice element 0
guard[1][1] = 40; // Cycle 1, Slice element 1
// guard[2][0] = 42; // Would panic: The data vec is only 2 repeat cycles long.
});

let thread1 = thread::spawn(move || {
// Lock slice offset 1:
let mut guard = lock1.try_lock(1).expect("Failed to lock offset.");

guard[0][0] = 100; // Cycle 0, Slice element 0
guard[0][1] = 200; // Cycle 0, Slice element 1
guard[1][0] = 300; // Cycle 1, Slice element 0
guard[1][1] = 400; // Cycle 1, Slice element 1
});

let thread2 = thread::spawn(move || {
// Lock slice offset 2:
let mut guard = lock2.try_lock(2).expect("Failed to lock offset.");

guard[0][0] = 1000; // Cycle 0, Slice element 0
guard[0][1] = 2000; // Cycle 0, Slice element 1
guard[1][0] = 3000; // Cycle 1, Slice element 0
guard[1][1] = 4000; // Cycle 1, Slice element 1
});

thread0.join();
thread1.join();
thread2.join();

// Get the data that has been modified by the threads.
let data = Arc::try_unwrap(lock).expect("Thread is still using data.").into_inner();

assert_eq!(data,
vec![10, 20, 100, 200, 1000, 2000,
30, 40, 300, 400, 3000, 4000]);


TODOs for future releases
=========================

The following new features might be candidates for future releases:

* Optimize the range overlap search algorithm.
* Sleeping lock, in case of lock contention.
* Add support for arrays.


License
=======

Copyright (c) 2021 Michael Buesch

Licensed under the Apache License version 2.0 or the MIT license, at your option.