A ShortIntroduction

to ServoWeb Engines Hackfest 2014

Martin Robinsonn@abandonedwig

The Modern BrowserFast JavaScript enginesOptimized layout routinesRapidly evolving rendering pipelinesEver increasing concurrency

Not GoodEnough

Not Good EnoughMemory safety issues leave users exposedWeb application complexity increasesLow amount of parallelism, leaving idle cores

Web Engine ParallelismWeb engines use fine-grained concurrency, but littleparallelismData structures not designed for parallelismDifficult to be parallel while ensuring memory safetyNative concurrency primitives not flexible

What We WantA safe and parallel web engine.

RustInitially Graydon Hoare's personal project, but adopted byMozilla Research in 2009.Fast, concurrent, safe compiled system languageThe compiler protects you from common memory issuesFast approaching version 1.0

What We WantA safe and parallel web engine.

Compile-time MemorySafety

fn main() { let mut vector = vec!(1i, 2i, 3i, 4i); let first_element = &vector[0]; vector.clear();

println!("Derferenced pointer to cleared value: {}", *first_element);}

error: cannot borrow ̀vector̀ as mutable because it is also borrowed as immutable...error: aborting due to previous error

What We WantA safe and parallel web engine.

Easy Concurrencylet (tx, rx) = channel();

spawn(proc() { tx.send("Hello from a task!".to_string());});

let message = rx.recv();println!("{}", message);

What We WantA safe and parallel web engine.

Task Data Safetylet mut x = vec!(1i, 2i, 3i);

spawn(proc() { println!("The value of x[0] is: {}", x[0]);});

println!("The value of x[0] is: {}", x[0]);

error: use of moved value: ̀x̀note: in expansion of format_args!<std macros>:2:23: 2:77 note: expansion site<std macros>:1:1: 3:2 note: in expansion of println!error: aborting due to previous error

Servoexperimental browser engine

by Mozilla Research

ServoParallel layout design from the startWork-stealing algorithm for task schedulingUse of green threads to allow creating many tasksModern rendering pipeline

ArchitectureConstellationConstellation

PipelinePipelineRenderRender Task Task

ScriptScript Task Task

LayoutLayout Task Task

PipelinePipelineRenderRender Task Task

ScriptScript Task Task

LayoutLayout Task Task

PipelinePipelineRenderRender Task Task

ScriptScript Task Task

LayoutLayout Task Task

Optimistically ParallelLayout

Parallelize layout as much as possibleA series of bottom-up and top-down passes on a flow treeSerialize when necessary, but hopefully uncommon orlimited casesSee speedup from parallelism on typical pages

Rendering PipelineAlways composited, no legacy approachesWorks divided into tasks

Layout Task: convert flow tree to display listRender Task: rasterize display list to shared surfacesCompositor Task: render rasterized content

Compositor layers are tiled and double-bufferedPinch zoom and panning support

Status

StatusMissing many CSS features and HTTP cachingForm interaction only in the early stagesHas evolving support for vertical writing modesVery close to dog-foodableCEF API for embedding

Get InvolvedDevelopment happens in the open, including roadmapOutside contributors very welcomeEverything available on Building is easy and fast compared to other enginesLook for bugs marked E-EasyDiscussion at #servo on irc.mozilla.org

Github

Demo

Questions