Browser process - detailed architecture overview

Startup

This is the entry point of the whole application (Main).
Main launches ContentMain and BrowserMain
BrowserMain starts the MainMessageLoop

Threads

Right after the startup the required threads are started

I/O thread

communication with the renderer task

DB thread

sqlite database connection and queries

Cache thread

cache store / retrieve

Worker threads

this is a facility that runs tasks that don't require a specific thread or a message loop
there is a thread pool called WorkerPool, which dynamically adds threads (if necessary) to handle all tasks
there are different implementations for POSIX and non-POSIX based systems

Loop

MainMessageLoop

is used to process events for a particular thread
puts the incoming messages, tasks to a queue
pops a task from the queue and starts it
strong relationship with the IPC communication framework
has task reentrancy protection

second task cannot be started until first task finishes

IPC / Mojo

framework which is used for inter-process communication
connects directly to the MainMessageLoop
provides communication channels through which the messages can be sent
message creating, sending and receiving
asynchronous message handling

TaskAnnotator

all incoming tasks are going through a TaskAnnotator which annotates the task before the execution
implements common debug annotations for posted tasks. This includes data such as task origins, queueing durations and memory usage
runs a previously queued task

ResourceLoader

browser side of the resource dispatcher
receives requests from the child processes (Renderer, Worker, etc)
dispatches the received requests to URLRequests
forwards the messages from the URLRequests back to the correct process for handling

URL

this group contains all the URL-relevant features
URL replacing and URL extension
URL autocomplete
extracting search terms from URL
URL parsing
URL canonicalization (picking the best URL, when there are multiple choices)
connection to Omnibox (Chromium’s “smart” URL bar)

SQL

classes which communicate with the sqlite3 database
load / update url autocomplete predictions from database
load saved favicons

net

NetworkDelegate

performs actions before the URLRequest starts

starts URLRequests
handles Cookies

loads all Cookies for a given URL async
sets all Cookies for the given URL

SSL Cert

handles SSL related actions
SSL handshake
certification verifying
signature verifying

Compositor (cc)

PaintFrame

painting main frame
prepare tiles
update layers
update picture layer
update display list
paint to display list
Aura’s painting is called

paint Tabs

Swap

draw to a specified surface
swap buffers

RasterTask

task, which performs rasterization
tasks are represented as a task graph

edges: dependencies
node: tasks, priority is assigned to them

items in the display list are drawn to the surface
the rasterization calls specific Skia functions in order to get the canvas drawn correctly

drawColor, drawPicture, drawRect, fillRect, etc.

X11/Windows/Mac

captures mouse, key, (etc) events and passes it to Chromium

UIEvent

classes in views and ui namespaces deal with all UI related functionalities
one of their important duties is handling UI events, for example mousemove, mouseclick, keypress, etc.
these events are passed forward from the system's Windowing library
the events are passed through an event handling chain in order to perform certain actions in each step
if the user enters the URL into the URLBar, these classes perform the character insertion into the URLBar’s text field.
Aura

UI framework, desktop window manager and shell environment
cross platform
Chrome OS uses it as well as Chrome / Chromium
Aura provides Window and Event types, as well as a set of interfaces to customize their behavior

Sources