Multiversion-concurrency-contro Alternatives

multiversion-concurrency-contro reviews and mentions

• Let's write a setjmp
  4 projects | news.ycombinator.com | 12 Feb 2023

  I wrote an unrolled switch statement in Java to simulate eager async/await across treads.

  https://github.com/samsquire/multiversion-concurrency-contro...

  The goal is that a compiler should generate this for you. This code is equivalent to the following:

     task1:

• Structured Concurrency Definition
  2 projects | news.ycombinator.com | 6 Feb 2023

  https://doc.rust-lang.org/book/ch16-00-concurrency.html

  I've been working on implementing Java async/await state machine with switch statements and a scheduling loop. If the user doesn't await the async task handle, then the task's returnvalue is never handled. This is similar to the Go problem with the go statement.

  https://github.com/samsquire/multiversion-concurrency-contro...

  If your async call returns a handle and

• Small VMs and Coroutines
  3 projects | news.ycombinator.com | 19 Jan 2023

  yield value2++

  https://github.com/samsquire/multiversion-concurrency-contro...

  I am still working on allowing multiple coroutines to be in flight in parallel at the same time. At the moment the tasks share the same background thread.

  I asked this stackoverflow question regarding C++ coroutines, as I wanted to use coroutines with a thread pool.

  https://stackoverflow.com/questions/74520133/how-can-i-pass-...

• Hctree is an experimental high-concurrency database back end for SQLite
  5 projects | news.ycombinator.com | 18 Jan 2023

  This is very interesting. Thank you for submitting this and thank you for working on this.

  I am highly interested in parallelism and high concurrency. I implemented multiversion concurrency control in Java.

  https://github.com/samsquire/multiversion-concurrency-contro...

  I am curious how to handle replication with high concurrency. I'm not sure how you detect dangerous reads+writes to the same key (tuples/fields) across different replica machines. In other words, multiple master.

  I am aware Google uses truetime and some form of timestamp ordering and detection of interfering timestamps. But I'm not sure how to replicate that.

  I began working on an algorithm to synchronize database records, do a sort, then a hash for each row where hash(row) = hash(previous_row.hash + row.data)

  Then do a binary search on hashes matching/not matching. This is a synchronization algorithm I'm designing that requires minimal data transfer but multiple round trips.

  The binary search would check the end of the data set for hash(replica_a.row[last]) == hash(replica_b.row[last]) then split the hash list in half and check the middle item, this shall tell you which row and which columns are different.

• Tail Call Optimization: The Musical
  2 projects | news.ycombinator.com | 8 Jan 2023

  https://github.com/samsquire/multiversion-concurrency-contro...

  I want to redesign the architecture of the async/await to be easier to understand. I want to use a state machine somehow.

• Rust Atomics and Locks: Low-Level Concurrency in Practice
  3 projects | news.ycombinator.com | 6 Jan 2023

  I wrote an unrolled state machine for my async/await in Java. This models a simple async/await program and runs tasks on other threads - without locks. I use a design I call token ring parallelism, where threads take turns and are linked together in a ring structure.

  https://github.com/samsquire/multiversion-concurrency-contro...

  I wrote a own lock free algorithm here that I use to do message passing between actor threads. My goal is high throughput performance and low latency.

  https://github.com/samsquire/multiversion-concurrency-contro...

  With 11 threads (on a 12 core processor, deliberately left one core for Windows)

• A Compiler Writing Playground
  3 projects | news.ycombinator.com | 26 Nov 2022

  I then started writing a parser for a high level language and then code generation from the AST to the imaginary assembly. My interpreter is multithreaded and can send integers between interpreters. It is very early and doesn't do much.

  Code is at https://github.com/samsquire/multiversion-concurrency-contro...

  The high level language looks similar to Javascript except I tried to parse everything as an expression. I need to parse functions as expressions.

  I was experimenting with Protothreads in C recently to try understand how it worked and I wrote a giant switch statement and a while loop in Java to simulate async/await. It would be interesting to do codegen for coroutines.

  here's that giant switch statement and scheduler https://github.com/samsquire/multiversion-concurrency-contro...

  One idea for a stackless design I had was to preallocate memory for each method call for a call to that function and avoid a stack altogether. This would allow coroutines between methods and avoid the function colour problem because everything is a coroutine.

  Is there any communities for programming language developers? Where do all the language developers meet up and talk theory and implementation? I am on eatonphil's discord and we talk there.

  One problem I am trying to understand how to solve is how you would write a multithreaded interpreter and language that allowed parallel interpretation similar to C# and Java. If the allocator is thread safe and you share an object pool between interpreters and you hash object equality by sourcecode, then you could send objects between threads with only a synchronization cost.

  I believe Python has the problem that object identity is different in each subinterpreter so you need to marshall the data.

• Safely writing code that isn't thread-safe: An under-appreciated Rust feature
  3 projects | news.ycombinator.com | 22 Nov 2022

  Thank you for writing this.

  I have worked on the same problem. It lead to me implementing multiversion concurrency control. Multiversion concurrency control allows thread safety avoiding locks except for internal data structures of the MVCC.

  Multiple threads can read/write the same data but they'll never modify the exact same data due to the multiple versions.

  https://github.com/samsquire/multiversion-concurrency-contro...

  I also implemented the bank account example but I serialised the account transactions in ConcurrentWithdrawer.java - this solution doesn't use multiversion concurrency control.

  My other solution BankAccounts2.java and BankAccounts3.java take different approaches.

  The BankAccounts2.java has 1 thread out of 11 threads that synchronizes the bank accounts and performs the serialization of account balances. The other threads generate transactions.

  BankAccounts3.java simply uses a lock.

  The problem with the bank accounts problem is that I am yet to work out how to scale it. You could shard threads to serve a certain range of account numbers.

  Or you can separate the current balance of each account across threads and if the receiving transaction is less than that balance, you don't need to read other threads to check.

• Software Mimicry
  3 projects | news.ycombinator.com | 19 Nov 2022

  I experiment with programming language theory and designs as a hobby and one of my thoughts is that the core underlying problem of computing is an arrangement problem of a turing machine. Compiling is "planning what you shall do". Execution is "doing". We have the luxury of many ways of doing things in computing. But it all seems to lead to mess of poor understandability and complexity.

  What am I trying to say? OOP inheritance hiarchy trees are limited and not what you really want to do to represent your problem. I want to define a situation or scenario and define what should happen in that scenario. This is where asynchronous programming and join calculus shines. I also like occam-pi's select statement and golang's select. I also feel every computing problem is the "expression problem" manifested. How do you associate behaviour (what to do) with a type (a situation)? And how do you define them so you don't have to reimplement all the previously existing behaviours with the new thing?

  The next section shall be reductive.

  Ultimately all loops, function application, methods, expressions, variables, classes, functions, lists, vectors, data structures, algorithms exist as "things" in the imagination of the developer's mind and the compiler. They don't exist in machine code.

  We have a grid of memory locations and the arrangement of things in that grid is handled by a memory allocator. We also have references in this grid as pointers, which form a structure of their own. A turing machine.

  Thinking of a type and behaviour as being solely one thing only at a time is inherently limiting. I often want to see different things "as" something else to talk about them in a slightly different approach. A vector or ArrayList of objects of multiple types but processed in the same approach, efficient compile time polymorphism.

  This is kind of how I imagine object orientated development to really be about, I want to be capable of referring to an arbitrary selection of objects and define new behaviours or relations between the objects. Unfortunately most OOP ties imperative behaviour and stateful manipulation to data rather than modify exhibited behaviours of objects. Imagine being capable of organising and managing load balancers and draining them and devops architecture with code. A point and click GUI where I can right click a load balancer and click drain. (I don't mean code to bring them up or create them but to actually administrate them with OOP)

  I think the expression problem is a core problem of modern computing and doesn't have an efficient solution.

  We can decouple data structure, layout and algorithm. Unfortunately most programming languages couple data structure + layout (C) and OOP languages couple algorithm with layout. Functional programming languages I'm not sure about.

  I called this idea of software mimicry as branching libraries in my ideas document (link in profile)

  I've been working with C++ templates today with C++20 coroutines and multithreading and I am finding template instantiation very interesting. I've been late to come around to it.

  This comment mentioned the insight that boxing and template instantiation are related. https://news.ycombinator.com/item?id=14764780

  I am also working on a multithreaded programming language which looks similar to Javascript. I use an actor implementation that can send messages between threads.

  https://github.com/samsquire/multiversion-concurrency-contro...

  One of my programming language designs is the idea that every line of code is a concurrent process and data flow is scheduled by topological sorting. Iteration is handled automatically for you. Every variable is actually a relation and algebraic definition of relations between processes. This is called algebralang. https://github.com/samsquire/algebralang

  The idea is that you write the underlying insight into the problem as an expression of what you want to do and let the computer schedule the ordering or arrangement of operations to do it. It's a form of pattern matching on the state of things (objects in the system) and declaration of the desired result. This brings to mind the rete algorithm (expert systems) and differential dataflow.

• An Introduction to Ractors in Ruby
  2 projects | news.ycombinator.com | 27 Aug 2022

  I wrote a parallel communicating thread actor model in Java that doesn't use mutuexes. I am yet to prove it is waitfree but it doesn't block, it always tries to move towards forward progress.

  I wrote a model checker in Python and it's slow as it tests every possible interleaving of the threads. I've run it a lot but there's the possibility there is a rare bug. But my model checker needs parallelising to prove the algorithm correct. So I need to parallelise my parallel algorithm checker.

  It's kind of based on https://www.cs.technion.ac.il/~erez/Papers/wfquque-ppopp.pdf in terms of work stealing (or helping)

  Every thread can communicate with every other thread and I load balance the pool with a simple atomic counter and modulo.

  https://github.com/samsquire/multiversion-concurrency-contro...

  I get 2 million communication events a second, so communication costs 500 nanoseconds. I plan to implement bidirectional communication so threads swap messages with each other, for double the throughput. The plan is that threads/actors have multiple event streams or sources of work, so they always have work to do even if there is contention.

  If you found this comment useful or interesting, check out my profile. I write of this stuff everyday.

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