//android_webview/renderer/

This folder holds WebView's renderer-specific code.

Folder dependencies

Like with other content embedders, //android_webview/renderer/ can depend on //android_webview/common/ but not //android_webview/browser/. It can also depend on content layer (and lower layers) as other embedders would (ex. can depend on //content/public/renderer/, //content/public/common/).

In-process renderer

WebView used to run in “single process” mode, which is when the renderer code runs inside the browser process on a separate thread called the renderer thread. Because this runs inside the browser process, there is no sandboxing (a compromised renderer has permission to access the disk or do anything else which the browser process is capable of).

Note: this is largely obsolete and irrelevant. The in-process renderer was the default on Lollipop (API 21) through Nougat MR1/MR2 (API 25), however modern WebView releases have dropped support for these versions.

Devices running Oreo (Api 26) through Q (API 29) will generally use an out-of-process renderer (see next section), however it's possible these will use in-process renderer on low-memory devices. However memory optimizations in Android R (API 30) mean that WebView always uses out-of-process renderer on Android R and above.

As of M139, the only supported configuration using single process mode is Android Q low-memory devices.

Out-of-process renderer

Starting in Oreo (API 26) WebView has a single out-of-process renderer (we sometimes refer to this as “multiprocess mode”). This is enabled for all 64-bit devices, for 32-bit devices with high memory, and for all devices starting in Android 11 (API 31). Low memory 32-bit devices running API26-30 still use an in-process renderer as before.

The out-of-process renderer is enabled by new Android APIs (android:externalService and Content.bindIsolatedService), to create sandboxed processes which run in the embedding app's context rather than the WebView provider's context. These processes will be named something like com.google.android.webview:sandboxed_process0 and it will run an Android service named org.chromium.content.app.SandboxedProcessService0. The package name will match the current WebView provider and the number suffix will usually be a 0 or a 1.

Without this API, we could only declare a fixed number of renderer processes to run in the WebView provider‘s context, and WebView (running in the app’s process) would have to pick one of these declared services to use as the renderer process. This would be a security problem because:

There‘s no trivial way for WebView (running in the app) to figure out which services are in-use, and reusing a service which is already in-use would mix content from two different apps in the same process (which violates Android’s trust model).
Even if we had a way to pick a not-in-use service, because WebView runs in the app's process, a malicious app could override this logic to intentionally pick an in-use service, with the goal of compromising another app on the system.
We have to declare a fixed number of services in the manifest. Even if we could securely put each app‘s content in a separate renderer process, supposing we’ve declared N services, the N+1th app will not have an empty service available and will have to share.

Running renderers in the app's context ensures content from two apps are always isolated, aligning with the Android security model.

Recovering from renderer crashes

Starting with Oreo, Android apps have the opportunity to recover from renderer crashes by overriding WebViewClient#onRenderProcessGone(). However, for backwards compatibility, WebView crashes the browser process if the app has not overridden this callback. Therefore, unlike in Chrome, renderer crashes are often non-recoverable.

Writing automated tests for either single process or multiprocess mode

You can annotate WebView javatests with @OnlyRunIn. See test instructions for details about how to use this annotation.

The default behavior (if no annotation is specified) is that the test will run in both modes.

Multiple renderers

Apps can create multiple WebView Profiles, in which case each Profile gets its own renderer process. Please see WebViewCompat.setProfile if you would like to use multiple Profiles for different WebView instances.

WebView does not generally support multiple renderer processes in a single profile, however this may be supported in the future. The only exception today is that WebView can create a separate renderer process for showing builtin error pages (known as webui in Chromium architecture), such as Safe Browsing interstitial warnings.