CAF Wasm support

[Dulaj Viduranga]

Hello,

I would like to know if there is a way to configure CAF to run synchronously on just a single thread (only the main thread). 

The requirement is that I have a system that is developed to support Desktop, Android (JNI), and Web (Wasm). The core code base is same for all platforms and separate wrappers are used to expose APIs. I decided to integrate an actor framework to the system and CAF is the obvious choice. I was able to do a test run on Android and it works perfectly.

However, due to the reason that the browsers have disabled multithreading support for wasm now, I cannot build CAF with emscripten for wasm. If there is a way not to use the default actor_system and do a synchronous message passing in the same thread, I would be able to use the same code base for all the platforms.

I would be thankful if anyone can provide some insights on how to tackle this problem. 

Thanks.

[Dominik Charousset]

Hi,

> I would like to know if there is a way to configure CAF to run synchronously on just a single thread (only the main thread).

The short answer is no. But there’s also a long answer. it’s not something I would usually recommend, since this comes with a couple of caveats.

There is a scheduler in CAF that does not spin up any threads. It’s called `test_coordinator` since we use it for writing deterministic unit tests.

You can configure CAF to use that instead of the work-stealing scheduler by setting the config parameter `cfg.set("scheduler.policy", caf::atom("testing"));`.

After that, you’ll notice that your application won’t do anything since you have to trigger everything manually now.

For that, you’ll need to get a reference to the scheduler: `auto& sched = dynamic_cast<caf::scheduler::test_coordinator&>(sys.scheduler());`.

The simplest way to just run everything is to call `sched.run()`, but you’ll notice that no timeout gets ever triggered. If you’re using `after()`, `delayed_send()`, requests with timeouts or anything like that, it’s going to get complicated. The test scheduler comes with a fake clock, so you’ll also have to manage time manually. If you’re using CAF’s new streams, this will also mess up credit management.

As long as you’re using a small subset of CAF and only rely on asynchronous messages, this might be feasible. However, anything that touches the clock is going to be tricky.


Hope I could provide at least some insights,
Dominik

[Dulaj Viduranga]

This is very helpful. I will test this out and post the results here for reference.

Thank you very much Dominik.

[Dulaj Viduranga]

This was fairly straight forward. The only thing is you have to disable all the additional threads from running.

    cfg.set("scheduler.policy", caf::atom("testing"));

    cfg.set("logger.verbosity", caf::atom("quite"));

did the trick. After that, you can get the scheduler as Dominik explained and use scheduler.run() after each send and receive to propagate the messages manually.