instance-copy-on-write

An experimental thread access synchronization primitive which is based on CoW Copy-on-Write and also exclusive lock.

The purpose of this crate to attempt to introduce a CoW method of syncing simpltanious data to shared memory between threads. The create is based on the crossbeam and atomics.

[!ATTENTION] By default an RwLock based implementation is used, because the atomics based implementation is still not ready. It can be activated by enabling the feature prefer_atomic.

The ICoWRead<DATA> instance with inner value DATA obtained from the ICoW<DATA> is valid even after the inner value was copied and copy was commited back. All readers which will will read the ICoW instance after the commit will receive a ICoWRead<DATA> with updated DATA.

Exclusive copying prevents readers from reading while simple non-exclusive copy allows to access the inner data for reading and further copying. But, the non-exclusive copies are not in sync, so each copy is uniq. The sequential commit of copied data is not yet supported.

Dual licensed crate.

This crate i.e code is NOT an Open Source software. This is a FREE (gratis) software and follows the principle of Sources Available/Disclosed software which must be fairly used.
It is published under FSF/OSI approved licenses however author does not follow/share/respect OSI and FSF principles and phylosophy.
License is subject to be changed in further versions without warning.
If you are using code in non-free (in terms of gratis) software you MUST NEVER demand a development of any features which are missing and needed for your business if you are not sponsoring/contributing those changes.
Access to the code can be limited by author to specific entities due to the local laws (not my bad or fault)(despite what is said in the license).

AI generated sloppy code is prohibited. AI generates slop "a priori" (anyway).
Licenses (thank you OSS sectarians ) do not anyhow limit AI training, but f^ck you all - ChatGPT, CockPilot, especially Claude and rest unidentified cr@p.
It is strongly discouraged from using the AI based tools to write or enhance the code. AI slope would 100% violate the license by introducing the 3rd party licensed code.

The pull requests are now supported because the repository was moved to Codeberg. The alternative way is to send patches over the email to patch[at]4neko.org.

In case if you would like to contribute the code, please use pull request. Your pull request should include:

Description of changes and why it is needed.
Test the pull request.

In case of you prefer email and patch files please consider the following:
For each feature or fix, please send patches separatly.
Please write what your patch is implementing or fixing.
I can read the code and I am able to understand it, so don't write a poem or essay in the description to the patches.
Please test your patch.

Version

v 0.6.0. Experimental.

Atomics was updated. Implemented another locking model which utilizes the transaction style which in theory is thread safe.
Added convertion into ICoWCopy from ICoWRead.
Added Weak referencing which could be obtained from ICoWRead. This would allow to detect if cached ICoWRead got outdated.
For the atomics, added a Waker which should wakeup the thread/s which was/were parked while waiting for the exclusive lock. Untested!
A ICoW::clone() and the rest functions which are related to clone_*() were renamed to clone_copy to avoid collisions with the Clone::clone().

Removed Send trait.

License change to MIT
Added Drop for ICoWLock to avoid dead locks.

Added new blocking methods.
Common tests are moved.

Added blocking functions.
Type of locking used.

Removed previous version.
Added two new realizations: atomic based and rwlock based.

License:

Sources are licensed with: MIT License

Description

There are three types of the operations:

Read-only reference
Copy-on-Write writing and storing
Exclusive copy-on-write (giant lock).

All read instances are valid all the time until dropeed, even if the CoW operation was performed.

After CoW instance commited, all new readers will see new value, all previous readers the previous value.

It was designed for the short period and small structures which can be copied. Also, where write operations can fail and the program is ok to use updated value.

An atocis-based CoW operation.

                              ┌─────────────────┐                                   
             ┌────────────────┤  ICoW<Instance> ┼───────────────┐                   
             ▼                └─────────┬───────┘               ▼                   
                                        │                                           
                                        ▼                                           
        ┌──────────┐             ┌─────────────┐      ┌────────────────────┐        
┌──────►│  read()  │◄────────────┤    copy(),  │      │ copy_exclusivly()  │        
│       └────┬─────┘          ^  │    clone()  │      │ clone_exclusivly() │        
│excl.lock   │                |  └─────────────┘      └─────────┬──────────┘        
│ repeat     │                |                                 │                   
│   ┌────────▼───────────┐    V  ┌────────────┐       ┌─────────▼──────────┐        
└───┼ compare_exchange() │    ┌► │ ICowCopy   │       │ compare_exchange() │        
    └────────┬───────────┘    │  └─────┬──────┘       │ self <- null_ptr   │        
             │  success       │        │              └─────────┬──────────┘        
             │                │        │                        │                   
      ┌──────▼──────┐         │        │               ┌────────▼──────────┐ locked 
      │   clone()   │         │        │               │      IF           │already 
      └──────┬──────┘         │        │               │ self == null_ptr  ┼───────┐
             │                │        │               └───────┬───────────┘       │
             │                │        │                       │                   │
             │                │        │                       │                   │
    ┌────────▼────────────┐   │        │              ┌────────▼────────────┐      │
    │ ICowRead<Instance>  ├───┘        │              │ ICowLock<Instance>  │      │
    └────────┬────────────┘            │              └────────┬────────────┘      │
             │                         │                       │                   │
             │                         ▼                       │                   │
             ▼                                                 │                   │
      ┌──────────────┐           ┌─────────────┐               │                   │
      │   / ... /    │           │  / ... /    │◄──────────────┘                   │
      └──────┬───────┘           └───┬────────┬┘                                   │
             │                       │  OR    │                                    │
             │                       │        │                                    │
     ┌───────▼─────┐         ┌───────▼──┐   ┌─▼────────┐                           │
     │  drop()     │         │ drop()   │   │ commit() │                           ▼
     └─────────────┘         └──────────┘   └──────────┘

Examples

Sync syslog (Local Shared)


let val = 
    ICoW::new(TestStruct::new(1, 2));

// read only 
let read1 = val.read();
//..
drop(read1);

// ...

// copy on write NON-exclusively, read is possible
let mut transaction = val.clone_copy();

transaction.start = 5;
transaction.stop = 6;

// update, after calling this function, all reades who 
// read before will still see old version.
// all reades after, new
transaction.commit();
//or
drop(transaction); // to drop changes


// exclusive lock, read is also not possible

let res = val.clone_copy_exclusivly();
// ..
// commit changes releasing lock
commit(val); //or
drop(val); // to drop changes and release lock

instance-copy-on-write 0.6.0