The progress of the legacy IPC migration in Chromium

Recall of the legacy IPCs migration

As you might know, Chromium has a multi-process architecture that involves many processes communicating with one another through IPC (Inter-Process Communication). However, traditionally IPC has used an approach which the Chromium project feels are not the best fit for achieving the project’s goals in terms of security, stability, and integration of a large number of components. Igalia has been working on many aspects of changing this. One very substantial effort has been in converting from the legacy named pipe IPC implementation to use the Mojo Framework. Mojo itself is approximately 3 times faster than the legacy IPC and involves one-third less context switching. We can remove unnecessary layers like //content/renderer layer to communicate between different processes. Besides we can easily connect interface clients and implementations across arbitrary inter-process boundaries. Thus, replacing the legacy IPC with Mojo is one of the goals for Onion Soup 2.0 [1] and it’s a prerequisite to further Onion Souping and refactoring. The uses of the legacy IPCs were very spread widely and blocking several high-impact projects including BackForwardCache, Multiple blink isolates, and RenderDocument. There were about 450 legacy IPC in January 2020. Approximately 264 IPCs in //content layer and there were 194 IPCs in the other areas.

The current Progress

Igalia has been working on converting the legacy IPCs to Mojo since 2020 in earnest. We have mainly focused on converting the legacy IPCs in //content during the last year. 293 messages have been migrated and 3 IPC messages remain. 98% has done since August 2019. As IPC messages conversion was almost done in //content layer at the end of March 2021, there are only 3 IPC messages related to Jin Java Bridge messages now. And also, recently we started working on other areas. For example, Printing, Extensions, Android WebView, and so on. 49 messages have been migrated and 150 messages still remain. 24% has done since August 2019. We have been working on migrating the legacy IPC to Mojo in other modules since BlinkOn 13. All IPCs were successfully completed to migrate to Mojo in Android WebView, Media, Printing modules since BlinkOn13. And now, Igalia has been working on converting in Extensions. Besides that, the Java legacy IPC conversion for the communication between C++ native and Java layer for Android was held for a while because there are some issues with WebView API in the content layer.
We have been working on migrating the legacy IPC to Mojo in other modules since BlinkOn 13. All IPCs were successfully completed to migrate to Mojo in Android WebView, Media, Printing modules since BlinkOn13. And now, Igalia has been working on converting in Extensions. Besides that, the Java legacy IPC conversion for the communication between C++ native and Java layers for Android was held for a while because there are some issues with WebView API in the content layer.