Creating a high priority task runner and a low priority task runner for the same sequence?

[Daniel Cheng]

I think the UI thread has some notion of this based on https://source.chromium.org/chromium/chromium/src/+/refs/heads/main:content/browser/scheduler/browser_task_queues.h;l=41;drc=78c31bec509b26c4fd92b386be58bf2fe3f14d91, but IIUC, it's built on top of base::SequenceManager, and that header looks a bit daunting without an example in the comments. Is there a simple way of doing this that already exists, or would we need to write our own?

(The use case here is prioritizing certain Mojo messages over others)

Daniel

[Etienne Pierre-doray]

This CL creates a new kUserInput queue that's kHighestPriority (see changes in content/public/browser).

 content::GetUIThreadTaskRunner({BrowserTaskType::kUserInput}) gets a task runner from this queue.

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[Gabriel Charette]

The default priority for content::GetUIThreadTaskRunner() is already base::TaskPriority::USER_BLOCKING (most tasks are a result of user interaction and hence this default makes the most sense).

To prioritize above that you need to specify (and probably add) a content::BrowserTaskType and define its underlying priority in content/browser/scheduler (BrowserTaskExecutor IIRC but offline as I write this)

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[Daniel Cheng]

What if I want to do this in a utility process, where presumably there is no UI thread?

Daniel

[Gabriel Charette]

Then you'll have to install a SequenceManager on the main thread, like BrowserTaskExecutor does.

The simplest example is SingleThreadTaskExecutor.

In fact, every non-pooled thread in Chrome, even base::Thread, has a SequenceManager (in the simple cases with only a single task queue).