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The ECMAScript proposal “ Shared memory and atomics ” by Lars T. Hansen has reached stage 4 this week and will be part of ECMAScript 2017. It introduces a new constructor SharedArrayBuffer and a namespace object Atomics with helper functions. This blog post explains the details. Parallelism vs. concurrency Before we begin, let’s clarify two terms that are similar, yet distinct: “parallelism” and “concurrency”. Many definitions for them exist; I’m using them as follows: Parallelism (parallel vs. serial): execute multiple tasks simultaneously Concurrency (concurrent vs. sequential): execute several tasks during overlapping periods of time (and not one after another). Both are closely related, but not the same: Parallelism without concurrency: single instruction, multiple data (SIMD). Multiple computations happen in parallel, but only a single task (instruction) is executed at any given moment. Concurrency without parallelism: multitasking via time-sharing on a single-core CPU. However,...

Occasionally, you want Web Workers to communicate with each other. Doing so is not obvious as most Web Worker examples are about communicating between the main thread and a Web Worker. There, one uses postMessage() to send messages directly to the Worker. Alas, that doesn’t work for communicating between two Workers, because you can’t pass references to Workers around. MessageChannel The solution is to establish a channel between the Workers: const channel = new MessageChannel(); receivingWorker.postMessage({port: channel.port1}, [channel.port1]); sendingWorker.postMessage({port: channel.port2}, [channel.port2]); We are creating a new MessageChannel and sending references to its two ports to two Workers. Every port can both send and receive messages. Note the second parameter of postMessage() : It specifies that channel.port1 and channel.port2 should be transfered (not copied) to the Workers. We can do that because MessagePort implements the interface Transferable . Po...

Recently , a new JavaScript feature has landed for the next Firefox Nightly: an API for SIMD (Single Instruction, Multiple Data). This blog post explains how the API works and how it fits into the JavaScript landscape. What is SIMD? SIMD is the ability of a CPU to apply an operand to vectors of values, instead of single values. For example, a CPU may be able to add two vectors v and w by adding their components, hence applying the single instruction addition to multiple data: v + w = 〈v 1 , …, v n 〉+ 〈w 1 , …, w n 〉 = 〈v 1 +w 1 , …, v n +w n 〉 SIMD brings speed-ups to many kinds of number crunching (3D computations, image processing, singal processing, etc.). John McCutchan (Google) and Peter Jensen (Intel) have proposed a JavaScript API for SIMD. That API initially grew out of the SIMD support in Dart, because Dart SIMD code needed to be compiled to JavaScript. At the moment, the API provides two data types: float32x4 (C type: __m128): four 32 bit floating point n...

Updates: [2015-01-05] ParallelJS has failed . It apparently wasn’t powerful enough. Its experimental implementation will be removed from SpiderMonkey (Firefox’s JavaScript engine). [2013-12-28] A low-level JavaScript API for SIMD is another avenue for parallelization (within a single processer core). JavaScript is still a very sequential language. That is slowly changing. This blog post describes ParallelJS , an effort to bring data parallelism to JavaScript. Background Concurrency versus parallelism Parallelism: more than one task is executed at the same time. That means that the tasks run on different processors or processor cores. Concurrency: more than one task makes progress at the same time. Often, tasks depend on each other. Concurrent tasks may run in parallel, but they can also be run via time slicing (virtual parallelism, if you will). These terms are not always used precisely, but the context usually makes it clear what is meant. Kinds of ...