[Webkit-unassigned] [Bug 220038] Unable to postMessage a WebAssembly module to a worklet

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=220038

--- Comment #10 from Yusuke Suzuki <ysuzuki at apple.com> ---
(In reply to Chris Dumez from comment #9)
> (In reply to Chris Dumez from comment #8)
> > (In reply to Chris Dumez from comment #7)
> > > (In reply to Richard Newman from comment #6)
> > > > I have not tested iframe messaging.
> > > > 
> > > > Web worker to page seems to work correctly.
> > > 
> > > Oh I see. If worker to page works then I would imagine iframe messaging
> > > would work too. This must be specific to worklets somehow.
> > 
> > In SerializedScriptValue:
> > 
> >                 if (m_context != SerializationContext::WorkerPostMessage) {
> >                     code = SerializationReturnCode::DataCloneError;
> >                     return true;
> >                 }
> > 
> > When encoding wasm modules. We are likely not using the WorkerPostMessage
> > SerializationContext when messaging audio worklets?
> 
> MessagePort::postMessage() seems to use the default serialization context,
> no matter in which context the message port is used:
> 
> ===
> ExceptionOr<void> MessagePort::postMessage(JSC::JSGlobalObject& state,
> JSC::JSValue messageValue, PostMessageOptions&& options)
> {
>     LOG(MessagePorts, "Attempting to post message to port %s (to be received
> by port %s)", m_identifier.logString().utf8().data(),
> m_remoteIdentifier.logString().utf8().data());
> 
>     registerLocalActivity();
> 
>     Vector<RefPtr<MessagePort>> ports;
>     auto messageData = SerializedScriptValue::create(state, messageValue,
> WTFMove(options.transfer), ports);
> ===

I changed it to WorkerPostMessage serialization context, and it didn't work because MessagePort always serialize (via IPC encoder) SerializedScriptValue and deserialized it even though both ports are used by the workers/worklets in the same process.
The problem is that we do not support full serialization of WebAssembly.Module.

1. It becomes super huge size
2. It is really complicated
3. Serialize and deserialize it will double memory size while WebAssembly.Module can be shared between multiple threads safely (it is designed to be a thread-safe).

So, we need a notion of "MessageChannel is not used among different processes", and we should avoid using IPC encoder / decoder to serialize SerializedScriptValue for MessagePort. And I think this is what gecko is doing.

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