https://github.com/ryan-williams/scalajs-worker-example

Proof of concept using web workers with scalajs (in particular, with scalajs-bundler)
https://github.com/ryan-williams/scalajs-worker-example

Last synced: about 2 months ago
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Proof of concept using web workers with scalajs (in particular, with scalajs-bundler)

• Host: GitHub
• URL: https://github.com/ryan-williams/scalajs-worker-example
• Owner: ryan-williams
• Created: 2019-01-01T20:42:08.000Z (about 6 years ago)
• Default Branch: master
• Last Pushed: 2019-01-01T22:34:54.000Z (about 6 years ago)
• Last Synced: 2024-10-20T07:45:26.568Z (3 months ago)
• Language: Scala
• Size: 9.77 KB
• Stars: 0
• Watchers: 2
• Forks: 0
• Open Issues: 0
• Metadata Files:
  • Readme: README.md

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README

        
# scalajs-worker-example

Proof of concept using web workers with scalajs (in particular, with scalajs-bundler), and discussion of some issues.

## Setup

```

# clone

git clone [email protected]:ryan-williams/scalajs-worker-example.git

cd scalajs-worker-example

# build

sbt worker/fastOptJS app/fastOptJS::webpack

# serve

cd app  # index.html and worker.js live here

python -m http.server

```

The app is then running at http://localhost:8000/

## Serializing Scala objects over the Worker API

[The `Serde` object](app/src/main/scala/App.scala#L26-38) shows a way of sending Scala objects over the Worker API by serializing to bytes using [boopickle](https://github.com/suzaku-io/boopickle), and dealing with JS byte-arrays using [the example of suzaku](https://github.com/suzaku-io/suzaku/blob/c1de595f5dba3277e3847837b719cfda5c1d6e0e/platform/web/core-shared/src/main/scala/suzaku/platform/web/WebWorkerTransport.scala#L27-L34).

[The main `App`'s send and receive code](app/src/main/scala/App.scala#L16-22) is then straightforward:

```scala

worker.onmessage = (msg: dom.MessageEvent) ⇒ {

  val foo = Serde[Foo](msg)

  println(s"received foo: $foo")

}

val foo = Foo(123, "abc")

worker.postMessage(Serde(foo))

```

and [the `Worker`'s](app/worker/src/main/scala/Worker.scala#L19-23) is similar:

```scala

def onMessage(msg: dom.MessageEvent) = {

  val foo = Serde[Foo](msg)

  val doubled = foo.copy(n = 2*foo.n)

  WorkerGlobal.postMessage(Serde(doubled))

}

``` 

## Separate SBT module for worker app

[Existing scalajs web-worker references I found](https://gist.github.com/ochrons/e4df27f1e6a56912471db163ef8eff73) don't account for problems that scalajs-bundler introduces. 

For example, the worker must run from a separate  "`worker.js`" script without a `window` object, and that goes through a different top-level entry-point than your main app, but [scalajs-bundler removes top-level exports](https://scalacenter.github.io/scalajs-bundler/cookbook.html#several-entry-points).

I worked around this by making the worker "application" its own SBT module (`worker`, in [the `app/worker` directory](app/worker)).

Nesting it under the main `app` module's directory made it easier for relevant scripts to see each other; for example, [`app`'s main object](app/src/main/scala/App.scala#L8) needs to run [`worker.js`](app/worker.js), which in turn needs to import [the `worker`'s generated JS application](app/worker/src/main/scala/Worker.scala) (`app/worker/target/scala-2.12/worker-fastopt.js`).

### Using scalajs-bundler in the worker module?

In this example, `worker` doesn't use scalajs-bundler, but in principle it might be able to, if you wanted it to use some NPM dependencies. However, that might usually fail; I think the worker's global scope doesn't include e.g. `require`, which is needed to load such dependencies