Published on March 7, 2014
CSP: Huh? And Components @TheHydroImpulse hydrocodedesign.com github.com/TheHydroImpulse
Communicating Sequential Processes
• I won’t be getting into the complex theory. • I’ll be going into the practical examples of CSP.
Concurrency What is it exactly?
Concurrency != Parallelism • • • Concurrency is a model for concurrent execution. Parallelism is the literal act of being concurrent. With concurrency, tasks are able to run at the same time, but they don’t have to — that’s parallelism.
CSP: Huh? • A formal language for describing patterns of interaction in concurrent systems. • based on message passing via channels.
Channels • A powerful primitive for communication • Channels are exactly what you think it is; they let you pass stuff through it. • Two basic actions: Put & Take Input Channel Output
Kinds of Channels Buffered Unbuffered (Can be dangerous)
Basic Actions • Put: Send a new value onto the channel • Take: Receive on existing value from the channel.
Channel Semantics • Semantics vary on the language/implementation. • The basic semantics are: • on share-ability of concrete channels. (i.e., across tasks/threads?) • when channels block
Blocking • Can block when trying to put a value onto the channel when it’s full. • Can block when trying to take a value from an empty channel.
What Blocks? • Very much dependent on the implementation/language. • Golang blocks on goroutines (a.k.a green threads) • Rust blocks on tasks (a.k.a green threads or native threads) • Clojure (core.async): both actions have the potential to block the underlying thread.
Clojure: core.async • A library not a language feature. • Goes to show how powerful a consistent language form (Lisp) can be, thanks to macros. • Supports unbounded buffered and bounded buffered channels. The former is discouraged. • Two implementations of the underlying “threads”. • Supports timeouts (super powerful) • All operations are expressions not statements. • Priority selects with alts!
Clojure: core.async • Supports two kinds of thread of control: • • • IoC (inversion of control) Normal Threads IoC threads are created with go blocks • go is a macro that examines it’s body for any channel operations and turns them into a state machine. • C#’s async does the same thing.
Callbacks (Direct Data-Flow) • Worst style of concurrency • You have no control over the data flow. • You’re (the callback) at the mercy of the caller.
Direct vs Indirect Direc t In Callback/Logic Out Indirec t In Channel Logic Channel Out
Indirect = Channels • Channels offer a better alternative at managing data-flow. • They are indirect. This means the logic is in control of the data-flow. • The logic can decide when it’s had too much data coming through. It’s the best decider at judging how much it can handle.
Examples! • Return the 5 fastest search queries. • Return the x number of queries that finish within 3 seconds (timeouts) • Channels act like queues. They’re a buffer for your data.
Components Building modular applications.
Components • Not an abstract component. • https://github.com/component/component • A client-side package manager and build tool. • CommonJS style code. • Ability to share client and server code super easily.
Unix Style • Build small, concentrated applications that do one thing, and does that thing extremely well. • Modular • Modular • Modular
Globals..grrr • Globals are horrible. Never use them. • Globals are horrible. Never use them. • Globals are horrible. Never use them. • jQuery, Angular, Ember, etc… ALL use them.
/** * Module Dependencies */ var dom = require('dom'); var model = require('tower-model'); var migration = require('tower-migration'); /** * User Model */ model('user') .attr('email') .validate('presence') .validate('isEmail') .attr('firstname') .attr('lastname') .attr('country') .attr('city'); /** * Migration */ migration.up('create_user_table') .model('user');
Creating a Component App
Modular Apps • It’s the future • Building monolithic apps suck • Tooling is only going to get better. • It’s much easier to wrap your head around a single module that has no side-effects (i.e., no external state & globals).
Server & Client-side • Node.js offers the ability to share code with the client-side (components). • Both have the same module pattern (CommonJS • Module can now be designed for both platforms.
No Globals? • We can take advantage of the module caching. • A version of inversion-of-control • Decentralized.
Module Caching • If each module is concentrated, you can store data (instances, values, etc…) in the module exports or module itself. • Example!
Wrapping Up • CSP is awesome. • Clojure is awesome. • Message passing & channels are awesome. • Modular apps are awesome. • Globals are horrible. • Callbacks are horrible.
Components & ES6 • Module system in ES6 replaces the build system in component. • Components might just become a package manager.
Thanks! @TheHydroImpuls e github.com/TheHydroImpulse hydrocodedesign.co m
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