[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 #11 from Chris Dumez <cdumez at apple.com> ---
(In reply to Yusuke Suzuki from comment #10)
> (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.

>From MessagePort, you can query identifier() and remoteIdentifier(). Each returns a MessagePortIdentifier which is a struct that contains both a processIdentifier and a portIdentifier. It should therefore be trivial to figure out if the local and remote ports are hosted in the same process check comparing identifier().processIdentifier and remoteIdentifier().processIdentifier.

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