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<nav id="sidebar" class="sidebar" aria-label="Table of contents"> <div class="sidebar-scrollbox"> <ol class="chapter"><li class="spacer"></li><li class="chapter-item expanded affix "><a href="introduction.html">Introduction</a></li><li class="chapter-item expanded affix "><li class="part-title">Processes</li><li class="chapter-item expanded "><a href="process-run.html"><strong aria-hidden="true">1.</strong> Running a Process</a></li><li class="chapter-item expanded "><a href="process-output.html"><strong aria-hidden="true">2.</strong> Output</a></li><li class="chapter-item expanded "><a href="process-input.html"><strong aria-hidden="true">3.</strong> Input</a></li><li class="chapter-item expanded "><a href="process-stderr.html"><strong aria-hidden="true">4.</strong> Stderr and Error Handling</a></li><li class="chapter-item expanded affix "><li class="part-title">Input/Output</li><li class="chapter-item expanded "><a href="io/read.html"><strong aria-hidden="true">5.</strong> Reading Stuff</a></li><li class="chapter-item expanded "><div><strong aria-hidden="true">6.</strong> Writing Stuff</div></li><li class="chapter-item expanded affix "><li class="part-title">Higher Order Functions for AsyncIterable</li><li class="chapter-item expanded "><div><strong aria-hidden="true">7.</strong> Enumeration</div></li><li class="chapter-item expanded "><div><strong aria-hidden="true">8.</strong> Compatibility with Streams</div></li><li class="chapter-item expanded "><a href="performance.html" class="active"><strong aria-hidden="true">9.</strong> Performance</a></li><li class="chapter-item expanded affix "><li class="part-title">Concurrency and Parallel Processing</li><li class="chapter-item expanded affix "><li class="part-title">Miscellaneous</li><li class="chapter-item expanded "><a href="misc/sleep.html"><strong aria-hidden="true">10.</strong> Sleep</a></li><li class="chapter-item expanded "><div><strong aria-hidden="true">11.</strong> Range</div></li><li class="chapter-item expanded "><div><strong aria-hidden="true">12.</strong> Shuffle</div></li><li class="chapter-item expanded affix "><li class="part-title">Concepts</li><li class="chapter-item expanded "><a href="text-data.html"><strong aria-hidden="true">13.</strong> Working with Text Data</a></li><li class="chapter-item expanded "><a href="transform.html"><strong aria-hidden="true">14.</strong> Transformers</a></li><li class="chapter-item expanded affix "><li class="part-title">Examples</li><li class="chapter-item expanded "><div><strong aria-hidden="true">15.</strong> Embed a Bash Script</div></li><li class="chapter-item expanded "><a href="example-counting-words.html"><strong aria-hidden="true">16.</strong> Counting Words</a></li><li class="chapter-item expanded "><a href="example-concurrent-processing.html"><strong aria-hidden="true">17.</strong> Concurrent Processing</a></li><li class="chapter-item expanded "><a href="example-io.html"><strong aria-hidden="true">18.</strong> Input and Output</a></li></ol> </div> <div id="sidebar-resize-handle" class="sidebar-resize-handle"> <div class="sidebar-resize-indicator"></div> </div> </nav>
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<h1 class="menu-title">proc</h1>
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<div id="content" class="content"> <main> <h1 id="performance"><a class="header" href="#performance">Performance</a></h1><p>A few notes on performance.</p><h2 id="does-performance-matter"><a class="header" href="#does-performance-matter">Does Performance Matter?</a></h2><p>For 90% of the code you write, the bottom line is that performance does notmatter. For example, if you have some code that reads configuration on startupand dumps it into an object, that code might be complicated, but it won't matterif it runs in 10 milliseconds or 100 nanoseconds. Write clear code first andoptimize once things are working. Follow this process, and you will quicklyfigure out which things do and don't matter.</p><h2 id="the-cost-of-iteration"><a class="header" href="#the-cost-of-iteration">The Cost of Iteration</a></h2><p>We use iteration everywhere. Doing it wrong can kill your performance. Doing itright can get you close to (single threaded) C performance. This is a quicksummary of what you can expect. To keep it short, I am just going to cover thehigh points and not show my work.</p><p>The fastest code you can write in pure JavaScript looks like<a href="https://en.wikipedia.org/wiki/Asm.js">asm.js</a>. If you stick to <code>for</code> loops thatcount and index simple types or data object lookups in arrays or numbers intyped-arrays (like <code>Uint8Array</code>), you can expect that code to run at or nearsingle-threaded C speed.</p><p>Expect <code>for...of</code> with iterables and generators to be about 10x slower. Thisincludes array methods like <code>map</code>, <code>filter</code>, and <code>reduce</code>. Anything that has tocall a function in a loop is going to have extra overhead.</p><p>Promise-driven asynchronous code is another 10x slower, or 100x slower than the<code>asm.js</code>-style code. This affects code written using <code>proc</code>, particularly<code>Enumerable</code>.</p><p>So does this mean you have to always use <code>asm.js</code> syntax? Not at all. <code>for...of</code>syntax and array methods make for cleaner code, and asynchronous operations arethe whole reason we're here. Iteration performance is mostly about the innerloops. If your inner loops are tight, a little less efficiency in the outerloops won't matter much. Write clean code first. When things are working, lookfor opportunities to make it faster. Often this will mean a little profiling andrewriting a few routines in <code>asm.js</code> style. If you do it right, you should beable to get very good performance along with readable code.</p><p><a href="https://medium.com/netscape/async-iterators-these-promises-are-killing-my-performance-4767df03d85b">Async Iterators: These Promises Are Killing My Performance!</a>on Medium and supporting benchmarks in<a href="https://github.com/danvk/async-iteration">async-iteration</a> on Github.</p><p><a href="https://madelinemiller.dev/blog/javascript-promise-overhead/">The Performance Overhead of JavaScript Promises and Async Await</a>shows a couple of examples that isolate the performance difference to overheaddue to promises.</p>
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